Name ARB_pixel_buffer_object Name Strings GL_ARB_pixel_buffer_object Notice Copyright (c) 2004-2013 The Khronos Group Inc. Copyright terms at http://www.khronos.org/registry/speccopyright.html Status Complete. Approved by ARB on December 7, 2004. Contributors Ralf Biermann Nick Carter Derek Cornish Matt Craighead Mark Kilgard Dale Kirkland Jon Leech Brian Paul Thomas Roell Ian Romanick Jeremy Sandmel Shazia Rahman Contact Mark J. Kilgard, NVIDIA Corporation (mjk 'at' nvidia.com) Ralf Biermann, NVIDIA Corporation (rbiermann 'at' nvidia.com) Derek Cornish, NVIDIA Corporation (dcornish 'at' nvidia.com) IP Status None. Version Last Modified Date: October 8, 2013 Revision: 1.2 Number ARB Extension #42 Dependencies Written based on the wording of the OpenGL 2.0 specification. Assumes support for (at least) OpenGL 1.5 or the ARB_vertex_buffer_object extension. NV_pixel_data_range affects the definition of this extension. EXT_pixel_buffer_object interacts with this extension. Overview This extension expands on the interface provided by the ARB_vertex_buffer_object extension (and later integrated into OpenGL 1.5) in order to permit buffer objects to be used not only with vertex array data, but also with pixel data. The intent is to provide more acceleration opportunities for OpenGL pixel commands. While a single buffer object can be bound for both vertex arrays and pixel commands, we use the designations vertex buffer object (VBO) and pixel buffer object (PBO) to indicate their particular usage in a given situation. Recall that buffer objects conceptually are nothing more than arrays of bytes, just like any chunk of memory. ARB_vertex_buffer_object allows GL commands to source data from a buffer object by binding the buffer object to a given target and then overloading a certain set of GL commands' pointer arguments to refer to offsets inside the buffer, rather than pointers to user memory. An offset is encoded in a pointer by adding the offset to a null pointer. This extension does not add any new functionality to buffer objects themselves. It simply adds two new targets to which buffer objects can be bound: GL_PIXEL_PACK_BUFFER and GL_PIXEL_UNPACK_BUFFER. When a buffer object is bound to the GL_PIXEL_PACK_BUFFER target, commands such as glReadPixels pack (write) their data into a buffer object. When a buffer object is bound to the GL_PIXEL_UNPACK_BUFFER target, commands such as glDrawPixels and glTexImage2D unpack (read) their data from a buffer object. There are a several approaches to improve graphics performance with PBOs. Some of the most interesting approaches are: - Streaming texture updates: If the application uses glMapBuffer/glUnmapBuffer to write its data for glTexSubImage into a buffer object, at least one of the data copies usually required to download a texture can be eliminated, significantly increasing texture download performance. - Streaming draw pixels: When glDrawPixels sources client memory, OpenGL says the client memory can be modified immediately after the glDrawPixels command returns without disturbing the drawn image. This typically necessitates unpacking and copying the image prior to glDrawPixels returning. However, when using glDrawPixels with a pixel pack buffer object, glDrawPixels may return prior to image unpacking because future modification of the buffer data requires explicit commands (glMapBuffer, glBufferData, or glBufferSubData). - Asynchronous glReadPixels: If an application needs to read back a number of images and process them with the CPU, the existing GL interface makes it nearly impossible to pipeline this operation. The driver will typically send the hardware a readback command when glReadPixels is called, and then wait for all of the data to be available before returning control to the application. Then, the application can either process the data immediately or call glReadPixels again; in neither case will the readback overlap with the processing. If the application issues several readbacks into several buffer objects, however, and then maps each one to process its data, then the readbacks can proceed in parallel with the data processing. - Render to vertex array: The application can use a fragment program to render some image into one of its buffers, then read this image out into a buffer object via glReadPixels. Then, it can use this buffer object as a source of vertex data. Issues 1) How does this extension relate to ARB_vertex_buffer_object? It builds on the ARB_vertex_buffer_object framework by adding two new targets that buffers can be bound to. 2) How does this extension relate to NV_pixel_data_range? This extension relates to NV_pixel_data_range in the same way that ARB_vertex_buffer_object relates to NV_vertex_array_range. To paraphrase the ARB_vertex_buffer_object spec, here are the main differences: - Applications are no longer responsible for memory management and synchronization. - Applications may still access high-performance memory directly, but this is optional, and such access is more restricted. - Buffer changes (glBindBuffer) are generally expected to be very lightweight, rather than extremely heavyweight (glPixelDataRangeNV). - A platform-specific allocator such as wgl/glXAllocateMemoryNV is no longer required. 3) Can a given buffer be used for both vertex and pixel data? RESOLVED: YES. All buffers can be used with all buffer bindings, in whatever combinations the application finds useful. Consider yourself warned, however, by the following issue. 4) May implementations make use of the target as a hint to select an appropriate memory space for the buffer? RESOLVED: YES, as long as such behavior is transparent to the application. Some implementations may choose, for example, that they would rather stream vertex data from AGP memory, element (index) data from video memory, and pixel data from video memory. In fact, one can imagine arbitrarily complicated heuristics for selecting the memory space, based on factors such as the target, the "usage" argument, and the application's observed behavior. While it is entirely legal to create a buffer object by binding it to GL_ARRAY_BUFFER and loading it with data, then using it with the GL_PIXEL_UNPACK_BUFFER_ARB or GL_PIXEL_PACK_BUFFER_ARB binding, such behavior is liable to confuse the driver and may hurt performance. If the driver implemented the hypothetical heuristic described earlier, such a buffer might have already been located in AGP memory, and so the driver would have to choose between two bad options: relocate the buffer into video memory, or accept lower performance caused by streaming pixel data from AGP. 5) Should all pixel path commands be supported, or just a subset of them? RESOLVED: ALL. While there is little reason to believe that, say, glConvolutionFilter2D would benefit from this extension, there is no reason _not_ to support it. The complete list of commands affected by this extension is listed in issues 17 and 18. 6) Should glPixelMap and glGetPixelMap be supported? RESOLVED: YES. They're not really pixel path operations, but, again, there is no good reason to omit operations, and they _are_ operations that pass around big chunks of pixel-related data. If we support glPolygonStipple, surely we should support this. 7) How does the buffer binding state push/pop? RESOLVED: As part of the pixel store client state. This is analogous to how the ARB_vertex_buffer_object bindings pushed/popped as part of the vertex array client state. 8) Should NV_pixel_data_range (PDR) be used concurrently with pixel buffer objects ? RESOLVED: NO. While it would be possible to allocate a memory range for PDR, using a pointer into this memory range with one of the commands affected by PBOs will not work if a pixel buffer object other than zero is bound to the buffer binding point affecting the command. Pixel buffer objects always have higher precedence than PDR. 9) Should the INVALID_OPERATION error be generated if a pixel command would access data outside the range of the bound PBO? RESOLVED: YES. This requires considering the command parameters (such as width/height/depth/format/type/pointer), the current pixel store (pack/unpack) state, and the command operation itself to determine the maximum addressed byte for the pixel command. Brian Paul strongly recommends this behavior. This behavior should increase the reliability of using PBO and guard against programmer mistakes. This is particularly important for glReadPixels where returning data into a region outside the PBO could cause corruption of application memory. Such bounds checking is substantially more expensive for VBO accesses because bounds checking on a per-vertex element basis for each of multiple enabled vertex arrays prior to performing the command compromises the performance justification of VBO. 10) If a pixel command with a bound PBO accesses data outside the range of the PBO, thereby generating a GL_INVALID_OPERATION error, can the pixel command end up being partially processed? RESOLVED: NO. As for all GL errors excepting GL_OUT_OF_MEMORY situations, "the command generating the error is ignored so that it has no effect on GL state or framebuffer contents." This means implementations must determine before the pixel command is performed whether the resulting read or write operations on the bound PBO will exceed the size of the PBO. This means an implementation is NOT allowed to detect out of bounds accesses in the middle of performing the command. 11) How expensive is it to predetermine whether a pixel command accessing a PBO would have an out of bounds access? See the "Appendix on Pack/Unpack Range" to see the computations involved in computing the access limit. Implementations can further specialize and optimize the check to make this out of bounds checking negligible for any sizable pixel payload. 12) Should feedback and select buffers output results into a buffer object? RESOLVED: That might be useful for a future extension but is not appropriate for this extension. New targets (other than PIXEL_PACK_BUFFER_ARB and PIXEL_UNPACK_BUFFER_ARB) make sense. 13) Should NV_pixel_data_range interactions be documented in this specification? RESOLVED: YES. Interactions with NV_pixel_data_range are important to document to facilitate developers migrating to the multi-vendor ARB_pixel_buffer_object extension. Discussion of interactions is limited to the issues and example usage sections. Other ARB specifications follow this policy, and Jon Leech agrees with this policy. 14) Should an INVALID_OPERATION error be generated if the offset within a pixel buffer to a datum comprising of N basic machine units is not a multiple of N? RESOLVED: YES. This was stated for VBOs but no error was defined if the rule was violated. Perhaps this needs to be better specified for VBO. For PBO, it is reasonable and cheap to enforce the alignment rule. For pixel commands it means making sure the offset is evenly divisible by the component or group size in basic machine units. This check is independent of the pixel store state because the pixel store state is specified in terms of pixels (not basic machine units) so pixel store addressing cannot create an unaligned access as long as the base offset is aligned. Certain commands (specifically glPolygonStipple, glGetPolygonStipple, glBitmap, glCompressedTexImage1D, glCompressedTexImage2D, glCompressedTexImage3D, glCompressedTexSubImage1D, glCompressedTexSubImage2D, glCompressedTexSubImage3D, and glGetCompressedTexImage) are not affected by this error because the data accessed is addressed at the granularity of basic machine units. 15) Various commands do not make explicit reference to supporting packing or unpacking from a pixel buffer object but rather specify that parameters are handled in the same manner as glDrawPixels, glReadPixels, or the glCompressedTexImage commands. So do such commands (example: glCompressedTexSubImage2D) use pixel buffers? RESOLVED: YES. Commands that have their behavior defined based on commands that read or write from pixel buffers will themselves read or write from pixel buffers. Relying on this reduces the amount of specification language to be updated. 16) What is the complete list of commands that can unpack (read) pixels from the current pixel unpack buffer object? glBitmap glColorSubTable glColorTable glCompressedTexImage1D glCompressedTexImage2D glCompressedTexImage3D glCompressedTexSubImage1D glCompressedTexSubImage2D glCompressedTexSubImage3D glConvolutionFilter1D glConvolutionFilter2D glDrawPixels glPixelMapfv glPixelMapuiv glPixelMapusv glPolygonStipple glSeparableFilter2D glTexImage1D glTexImage2D glTexImage3D glTexSubImage1D glTexSubImage2D glTexSubImage3D 17) What is the complete list of commands that can pack (write) pixels into the current pixel pack buffer object? glGetCompressedTexImage glGetConvolutionFilter glGetHistogram glGetMinmax glGetPixelMapfv glGetPixelMapuiv glGetPixelMapusv glGetPolygonStipple glGetSeparableFilter, glGetTexImage glReadPixels 18) How does support for pixel buffer objects affect the GLX protocol? UNRESOLVED: See the "GLX Protocol" section. 19) Prior to this extension, passing zero for the data argument of glTexImage1D, glTexImage2D, and glTexImage3D defined a texture image level without supplying an image. How does this behavior change with this extension? RESOLVED: The "unspecified image" behavior of the glTexImage calls only applies when bound to a zero pixel unpack buffer object. When bound to a non-zero pixel unpack buffer object, the data argument to these calls is treated as an offset rather than a pointer so zero is a reasonable and even likely value that corresponds to the very beginning of the buffer object's data. So to create a texture image level with unspecified image data, you MUST bind to the zero pixel unpack buffer object. See the ammended language at the end of section 3.8.1. 20) How does this extension support video frame grabbers? RESOLVED: This extension extends buffer objects so they can operate with pixel commands, rather than just vertex array commands. We anticipate that a future extension may provide a mechanism for transferring video frames from video frame grabber hardware or vertices from motion capture hardware (or any other source of aquired real-time data) directly into a buffer object to eliminate a copy. Ideally, such transfers would be possible without requiring mapping of the buffer object. But this extension does not provide such functionality. We anticipate such functionality to involve binding a buffer object to a new target type, configuring a source (or sink) for data (video frames, motion capture vertex sets, etc.), and then commands to initiate data transfers to the bound buffer object. 21) Can this ARB extension share the same enumerants with the EXT version of this functionality? RESOLVED: YES. The ARB extension is functionally compatible with EXT_pixel_buffer_object except that the ARB version adds additional error checks for alignment and buffer bounds checking. The EXT behavior in the case of alignment violations and buffer bounds overflow are technically undefined. The ARB extension simply defines the EXT extension's undefined behavior to be an OpenGL error. Using the same enumerants with firmed up error checking (that would otherwise indicate buggy usage) is preferable to two sets of enumerants where the older EXT set simply allows sloppy usage. 22) The expected usage parameters (GL_STREAM_DRAW, etc.) for glBufferData are not clearly specified. How can they be improved? RESOLVED: To improve the clarity, replace the phrase "specified once" with "specified once per repetition of the usage pattern" so that it is clear for the STREAM_* usage modes (and the STATIC_* usage modes too, just much less frequently) that the repeated specification is part of a pattern and it is expected that the buffer can be, and will be for the STREAM_* usage patterns, specified again after being used and this is likely to repeat. Additionally, the *_COPY and *_DRAW usage patterns can source the data with "a GL drawing command" but also with image specification commands so change this phrase to "a GL drawing or image specification command." 23) Is this the "right" way to expose render-to-vertex-array? DISCUSSION: You can use this extension to render an image into a framebuffer, copy the pixels into a buffer object with glReadPixels, and then configure vertex arrays to source the pixel data as vertex attributes. This necessarily involves a copy from the framebuffer to the buffer object. Future extensions may provide mechanisms for copy-free render-to-vertex-array capabilities but that is not a design goal of this extension. New Procedures and Functions None. New Tokens Accepted by the parameters of BindBuffer, BufferData, BufferSubData, MapBuffer, UnmapBuffer, GetBufferSubData, GetBufferParameteriv, and GetBufferPointerv: PIXEL_PACK_BUFFER_ARB 0x88EB PIXEL_UNPACK_BUFFER_ARB 0x88EC Accepted by the parameter of GetBooleanv, GetIntegerv, GetFloatv, and GetDoublev: PIXEL_PACK_BUFFER_BINDING_ARB 0x88ED PIXEL_UNPACK_BUFFER_BINDING_ARB 0x88EF Additions to Chapter 2 of the GL Specification (OpenGL Operation) None -- Section 2.9 "Buffer Objects" Replace the first two paragraphs with: "The vertex data arrays described in section 2.8 are stored in client memory. It is sometimes desirable to store frequently accessed client data, such as vertex array and pixel data, in high-performance server memory. GL buffer objects provide a mechanism for clients to use to allocate, initialize, and access such memory." The name space for buffer objects is the unsigned integer, with zero reserved for the GL. A buffer object is created by binding an unused name to a buffer target. A buffer object is bound by calling void BindBuffer(enum target, uint buffer); /target/ must be one of ARRAY_BUFFER, ELEMENT_ARRAY_BUFFER, PIXEL_UNPACK_BUFFER_ARB, or PIXEL_PACK_BUFFER_ARB. The ARRAY_BUFFER target is discussed in section 2.9.1 The ELEMENT_ARRAY_BUFFER target is discussed in section 2.9.2. The PIXEL_UNPACK_BUFFER_ARB and PIXEL_PACK_BUFFER_ARB targets are discussed later in sections 3.6, 4.3.2, and 6.1. If the buffer object named /buffer/ has not been previously bound or has been deleted since the last binding, the GL creates a new state vector, initialized with a zero-sized memory buffer and comprising the state values listed in table 2.6." Replace the 5th paragraph with: "Initially, each buffer object target is bound to zero. There is no buffer object corresponding to the name zero so client attempts to modify or query buffer object state for a target bound to zero generate an INVALID_OPERATION error." Replace the phrase listing the valid targets for BufferData in the 9th paragraph with: "with target set to one of ARRAY_BUFFER, ELEMENT_ARRAY_BUFFER, PIXEL_UNPACK_BUFFER_ARB, or PIXEL_PACK_BUFFER_ARB," In the 10th paragraph describing buffer object usage modes, replace the phrase "specified once" with "specified once per repetition of the usage pattern" for the STREAM_* and STATIC_* usage values. Also in the 10th paragraph describing buffer object usage modes, replace the phrases "of a GL drawing command." and "for GL drawing commands." with "for GL drawing and image specification commands." for the *_DRAW and *_COPY usage values. Replace the phrase listing the valid targets for BufferSubData in the 15th paragraph with: "with target set to one of ARRAY_BUFFER, ELEMENT_ARRAY_BUFFER, PIXEL_UNPACK_BUFFER_ARB, or PIXEL_PACK_BUFFER_ARB." Replace the phrase listing the valid targets for MapBuffer in the 16th paragraph with: "with target set to one of ARRAY_BUFFER, ELEMENT_ARRAY_BUFFER, PIXEL_UNPACK_BUFFER_ARB, or PIXEL_PACK_BUFFER_ARB." Replace the phrase listing the valid targets for UnmapBuffer in the 21st paragraph with: "with target set to one of ARRAY_BUFFER, ELEMENT_ARRAY_BUFFER, PIXEL_UNPACK_BUFFER_ARB, or PIXEL_PACK_BUFFER_ARB." -- Section 2.9.2 "Array Indices in Buffer Objects" Delete the 3rd paragraph that explains how the ELEMENT_ARRAY_BUFFER target is acceptable for the commands specified in section 2.9. The updated section 2.9 language already says this. -- NEW Section 2.9.3 "Buffer Object Required State" "The state required to support buffer objects consists of binding names for the array buffer, element buffer, pixel unpack buffer, and pixel pack buffer. Additionally, each vertex array has an associated binding so there is a buffer object binding for each of the vertex array, normal array, color array, index array, multiple texture coordinate arrays, edge flag array, secondary color array, fog coordinate array, and vertex attribute arrays. The initial values for all buffer object bindings is zero. The state of each buffer object consists of a buffer size in basic machine units, a usage parameter, an access parameter, a mapped boolean, a pointer to the mapped buffer (NULL if unmapped), and the sized array of basic machine units for the buffer data." Additions to Chapter 3 of the 1.2.1 Specification (Rasterization) -- Section 3.6 "Pixel Rectangles" Replace the 1st sentence in the 2nd paragraph: "A number of parameters control the encoding of pixels in buffer object or client memory (for reading and writing) and how pixels are processed before being placed in or after being read from the framebuffer (for reading, writing, and copying)." -- RENAME Section 3.6.1 "Pixel Storage Modes and Pixel Buffer Objects" Add to the end of the section: "In addition to storing pixel data in client memory, pixel data may also be stored in buffer objects (described in section 2.9). The current pixel unpack and pack buffer objects are designated by the PIXEL_UNPACK_BUFFER_ARB and PIXEL_PACK_BUFFER_ARB targets respectively. Initially, zero is bound for the PIXEL_UNPACK_BUFFER_ARB, indicating that image specification commands such as DrawPixels source their pixels from client memory pointer parameters. However, if a non-zero buffer object is bound as the current pixel unpack buffer, then the pointer parameter is treated as an offset into the designated buffer object." -- Section 3.6.3 "Pixel Transfer Modes", page 116. Replace the last phrase in the 2nd paragraph with: "and /values/ refers to an array of size map values." [values is no longer necessarily a pointer.] Add the following paragraph after the third paragraph: "If a pixel unpack buffer is bound (as indicated by a non-zero value of PIXEL_UNPACK_BUFFER_BINDING_ARB), /values/ is an offset into the pixel unpack buffer; otherwise, /values/ is a pointer to a block client memory. All pixel storage and pixel transfer modes are ignored when specifying a pixel map. n machine units are read where n is the /size/ of the pixel map times the size of a float, uint, or ushort datum in basic machine units, depending on the respective PixelMap version. If a pixel unpack buffer object is bound and data+n is greater than the size of the pixel buffer, INVALID_OPERATION results. If a pixel unpack buffer object is bound and /values/ is not evenly divisible into the number of basic machine units needed to store in memory a float, uint, or ushort datum depending on their respective PixelMap version, INVALID_OPERATION results." -- Section 3.6.4 "Rasterization of Pixel Rectangles", page 126. Change the 1st sentence of the 1st paragraph to read: "The process of drawing pixels encoded in buffer objects or client memory is diagrammed in figure 3.7." Change the 4th sentence of the 2nd paragraph to read: "/data/ refers to the data to be drawn." [data is no longer necessarily a pointer.] Change the initial phrase in the 1st sentence of the 1st paragraph after "Unpacking" to read: "Data are taken from the currently bound pixel unpack buffer or client memory as a sequence of..." Insert this paragraph after the 1st paragraph after "Unpacking": "If a pixel unpack buffer is bound (as indicated by a non-zero value of PIXEL_UNPACK_BUFFER_BINDING_ARB), /data/ is an offset into the pixel unpack buffer and the pixels are unpacked from the buffer relative to this offset; otherwise, /data/ is a pointer to a block client memory and the pixels are unpacked from the client memory relative to the pointer. If a pixel unpack buffer object is bound and unpacking the pixel data according to the process described below would access memory beyond the size of the pixel unpack buffer's memory size, INVALID_OPERATION results. If a pixel unpack buffer object is bound and /data/ is not evenly divisible into the number of basic machine units needed to store in memory the corresponding GL data type from table 3.5 for the /type/ parameter, INVALID_OPERATION results." -- Section 3.8.1 "Texture Image Specification", page 150. Replace the last phrase in the 2nd to last sentence in the 1st paragraph with: "and a reference to the image data in the currently bound pixel unpack buffer or client memory." Replace the 1st sentence in the 13th paragraph with: "The image itself (referred to by /data/) is a sequence of groups of values." Replace the last paragraph with: "If the data argument of TexImage1D, TexImage2D, or TexImage3D is a null pointer (a zero-valued pointer in the C implementation) and the pixel unpack buffer object is zero, a one-, two-, or three- dimensional texture array is created with the specified target, level, internalformat, width, height, and depth border, but with unspecified image contents. In this case no pixel values are access in client memory, and no pixel processing is performed. Errors are generated, however, exactly as though the data pointer were valid. Otherwise if the pixel unpack buffer object is non-zero, the data argument is treatedly normally to refer to the beginning of the pixel unpack buffer object's data." -- Section 3.8.3 "Compressed Texture Images", page 163. Replace the 3rd sentence of the 2nd paragraph with: "/data/ refers to compressed image data stored in the compressed image format corresponding to internalformat. If a pixel unpack buffer is bound (as indicated by a non-zero value of PIXEL_UNPACK_BUFFER_BINDING_ARB), /data/ is an offset into the pixel unpack buffer and the compressed data is read from the buffer relative to this offset; otherwise, /data/ is a pointer to a block client memory and the compressed data is read from the client memory relative to the pointer." Replace the 2nd sentence in the 3rd paragraph with: "Compressed texture images are treated as an array of /imageSize/ ubytes relative to /data/. If a pixel unpack buffer object is bound and data+imageSize is greater than the size of the pixel buffer, INVALID_OPERATION results." Additions to Chapter 4 of the 1.2.1 Specification (Per-Fragment Operations and the Frame Buffer) -- Section 4.3.2 "Reading Pixels", page 219. Replace 1st sentence of the 1st paragraph with: "The method for reading pixels from the framebuffer and placing them in pixel pack buffer or client memory is diagrammed in figure 4.2." Add this paragraph after the 1st paragraph: "Initially, zero is bound for the PIXEL_PACK_BUFFER_ARB, indicating that image read and query commands such as ReadPixels return pixels results into client memory pointer parameters. However, if a non-zero buffer object is bound as the current pixel pack buffer, then the pointer parameter is treated as an offset into the designated buffer object." Rename "Placement in Client Memory" to "Placement in Pixel Pack Buffer or Client Memory". Insert this paragraph after the newly renamed "Placement in Pixel Pack Buffer or Client Memory" heading: "If a pixel pack buffer is bound (as indicated by a non-zero value of PIXEL_PACK_BUFFER_BINDING_ARB), /data/ is an offset into the pixel pack buffer and the pixels are packed into the buffer relative to this offset; otherwise, /data/ is a pointer to a block client memory and the pixels are packed into the client memory relative to the pointer. If a pixel pack buffer object is bound and packing the pixel data according to the pixel pack storage state would access memory beyond the size of the pixel pack buffer's memory size, INVALID_OPERATION results. If a pixel pack buffer object is bound and /data/ is not evenly divisible into the number of basic machine units needed to store in memory the corresponding GL data type from table 3.5 for the /type/ parameter, INVALID_OPERATION results." Additions to Chapter 5 of the 1.2.1 Specification (Special Functions) None Additions to Chapter 6 of the 1.2.1 Specification (State and State Requests) -- Section 6.1.3 "Enumerated Queries". After the sentence in the last paragraph describing GetPixelMap, add: "The GetPixelMapfv, GetPixelMapuiv, and GetPixelMapusv commands write all the values in the named pixel map to /data/. If a pixel pack buffer is bound (as indicated by a non-zero value of PIXEL_PACK_BUFFER_BINDING_ARB), /data/ is an offset into the pixel pack buffer; otherwise, /data/ is a pointer to a block client memory. All pixel storage and pixel transfer modes are ignored when returning a pixel map. n machine units are written where n is the size of the pixel map times the size of FLOAT, UNSIGNED_INT, or UNSIGNED_SHORT respectively in basic machine units. If a pixel pack buffer object is bound and data+n is greater than the size of the pixel buffer, generate INVALID_OPERATION." -- Section 6.1.4 "Texture Queries". Remove the mention of img in the last phrase in the last sentence of the 1st paragraph so the sentence reads: "lod is a level-of-detail number, format is a pixel format from table 3.6, and type is a pixel type from table 3.5." Replace the 3rd sentence of the 2nd paragraph with: "These groups are then packed and placed in client or pixel buffer object memory. If a pixel pack buffer is bound (as indicated by a non-zero value of PIXEL_PACK_BUFFER_BINDING_ARB), /img/ is an offset into the pixel pack buffer; otherwise, /img/ is a pointer to a block client memory." Add to the end of the 4th paragraph: "If a pixel pack buffer object is bound and packing the texture image into the buffer's memory would exceed the size of the buffer, generate INVALID_OPERATION." Replace the 2nd sentence of the 5th paragraph with: "When called, GetCompressedTexImage writes n ubytes of compressed image data to the pixel pack buffer or client memory pointed to by ptr, where n is the texture image's TEXTURE_COMPRESSED_IMAGE_SIZE value. Add to the end of the 6th paragraph: "If a pixel pack buffer object is bound and ptr+n is greater than the size of the buffer, generate INVALID_OPERATION." -- Section 6.1.5 "Stipple Query". "The pattern is packed into client or pixel pack buffer memory according to the procedures given in section 4.3.2 for ReadPixels; ..." -- Section 6.1.7 "Color Table Query". "The one-dimensional color table image is returned to client or pixel pack buffer memory starting at table." -- Section 6.1.8 "Convolution Query". "The one-dimensional or two-dimensional image is returned to client or pixel pack buffer memory starting at image." "The row and column images are returned to client or pixel pack buffer memory starting at row and column respectively." -- Section 6.1.9 "Histogram Query". "The one-dimensional histogram table image is returned to client or pixel pack buffer memory starting at values." -- Section 6.1.10 "Minmax Query". "A one-dimensional image of width 2 is returned to client or pixel pack buffer memory starting at values." -- Section 6.1.13 "Buffer Object Queries". Change the 2nd sentence of the 2nd paragraph to read: "target is ARRAY_BUFFER, ELEMENT_ARRAY_BUFFER, PIXEL_PACK_BUFFER_ARB, or PIXEL_UNPACK_BUFFER_ARB." Change the last phrase in the 1st sentence of the 4th paragraph to: "with target set to ARRAY_BUFFER, ELMENT_ARRAY_BUFFER, PIXEL_PACK_BUFFER_ARB, or PIXEL_UNPACK_BUFFER_ARB and pname set to BUFFER_MAP_POINTER." GLX Protocol Pixel buffers, like texture objects and display lists, are server-side state. Prior to pixel buffer objects, pixel storage state for image packing and unpacking was considered client-side state. However, pixel buffers create the new situation where the server performs packing and unpacking into server-side pixel buffers. Fortunately, the GLX protocol, through foresight or oversight, has GLX protocol and non-rendering command opcodes (109 and 110) assigned for glPixelStoref and glPixelStorei respectively. It is better to use the existing protocol to send glPixelStorei and glPixelStoref GLX commands. This solves the problem of server-side pixel state the same way for both pack and unpack state. It may also allow implementations to minimize validation overhead for pixel commands because the pixel store modes are stateful rather than being parameters sent with every pixel command. When bound to a pixel unpack buffer object, the pixel payload for a pixel command with no reply (for exmaple, glTexImage2D) is not sent. Instead, the pointer itself is sent as a 64-bit offset. Pixel storage modes are also not included in non-reply pixel commands. Therefore, the following new protocol for pixel commands that use the currently bound pixel unpack buffer object is specified: BitmapPBO ColorSubTablePBO ColorTablePBO CompressedTexImage1DPBO CompressedTexImage2DPBO CompressedTexImage3DPBO CompressedTexSubImage1DPBO CompressedTexSubImage2DPBO CompressedTexSubImage3DPBO ConvolutionFilter1DPBO ConvolutionFilter2DPBO DrawPixelsPBO PixelMapfvPBO PixelMapuivPBO PixelMapusvPBO PolygonStipplePBO SeparableFilter2DPBO TexImage1DPBO TexImage2DPBO TexImage3DPBO** TexSubImage1DPBO TexSubImage2DPBO TexSubImage3DPBO When bound to a pixel pack buffer object, the reply for pixel commands that return pixel data (for example, glReadPixels) is not required since the pixel data is actually transferred to the server-side pixel pack buffer object. Indeed, forcing an unnecessary reply would hinder the performance advantages of using pixel buffer objects Therefore, protocol for "no reply" version of the following commands is specified: GetColorTablePBO GetCompressedTexImagePBO GetConvolutionFilterPBO GetHistogramPBO GetMinmaxPBO GetPixelMapfvPBO GetPixelMapuivPBO GetPixelMapusvPBO GetPolygonStipplePBO GetSeparableFilterPBO GetTexImagePBO ReadPixelsPBO If a "no reply" command is sent when the current pixel pack buffer object binding is zero, a GLXBadContextState error should be generated by the server. The following rendering commands are sent to the server as part of a glXRender request: BitmapPBO 2 36 rendering command length 2 311 rendering command opcode 8 CARD64 bitmap 4 CARD32 width 4 CARD32 height 4 FLOAT32 xorig 4 FLOAT32 yorig 4 FLOAT32 xmove 4 FLOAT32 ymove ColorSubTablePBO 2 32 rendering command length 2 312 rendering command opcode 8 CARD64 table 4 ENUM target 4 CARD32 start 4 CARD32 count 4 ENUM apiFormat 4 ENUM apiType ColorTablePBO 2 32 rendering command length 2 313 rendering command opcode 8 CARD64 table 4 ENUM target 4 ENUM internalformat 4 CARD32 width 4 ENUM apiFormat 4 ENUM apiType CompressedTexImage1DPBO 2 36 rendering command length 2 314 rendering command opcode 8 CARD64 data 4 ENUM target 4 CARD32 level 4 ENUM internalFormat 4 CARD32 width 4 CARD32 border 4 CARD32 imageSize CompressedTexImage2DPBO 2 40 rendering command length 2 315 rendering command opcode 8 CARD64 data 4 ENUM target 4 CARD32 level 4 ENUM internalFormat 4 CARD32 width 4 CARD32 height 4 CARD32 border 4 CARD32 imageSize CompressedTexImage3DPBO 2 44 rendering command length 2 316 rendering command opcode 8 CARD64 data 4 ENUM target 4 CARD32 level 4 ENUM internalFormat 4 CARD32 width 4 CARD32 height 4 CARD32 depth 4 CARD32 border 4 CARD32 imageSize CompressedTexSubImage1DPBO 2 36 rendering command length 2 317 rendering command opcode 8 CARD64 data 4 ENUM target 4 CARD32 level 4 CARD32 xoffset 4 CARD32 width 4 ENUM apiFormat 4 CARD32 imageSize CompressedTexSubImage2DPBO 2 44 rendering command length 2 318 rendering command opcode 8 CARD64 data 4 ENUM target 4 CARD32 level 4 CARD32 xoffset 4 CARD32 yoffset 4 CARD32 width 4 CARD32 height 4 ENUM apiFormat 4 CARD32 imageSize CompressedTexSubImage3DPBO 2 52 rendering command length 2 319 rendering command opcode 8 CARD64 data 4 ENUM target 4 CARD32 level 4 CARD32 xoffset 4 CARD32 yoffset 4 CARD32 zoffset 4 CARD32 width 4 CARD32 height 4 CARD32 depth 4 ENUM apiFormat 4 CARD32 imageSize ConvolutionFilter1DPBO 2 32 rendering command length 2 320 rendering command opcode 8 CARD64 image 4 ENUM target 4 ENUM internalformat 4 CARD32 width 4 ENUM apiFormat 4 ENUM apiType ConvolutionFilter2DPBO 2 36 rendering command length 2 321 rendering command opcode 8 CARD64 image 4 ENUM target 4 ENUM internalformat 4 CARD32 width 4 CARD32 height 4 ENUM apiFormat 4 ENUM apiType DrawPixelsPBO 2 28 rendering command length 2 322 rendering command opcode 8 CARD64 image 4 CARD32 width 4 CARD32 height 4 ENUM apiFormat 4 ENUM apiType PixelMapfvPBO 2 20 rendering command length 2 323 rendering command opcode 8 CARD64 values 4 ENUM map 4 CARD32 mapsize PixelMapuivPBO 2 20 rendering command length 2 324 rendering command opcode 8 CARD64 values 4 ENUM map 4 CARD32 mapsize PixelMapusvPBO 2 20 rendering command length 2 325 rendering command opcode 8 CARD64 values 4 ENUM map 4 CARD32 mapsize PolygonStipplePBO 2 12 rendering command length 2 326 rendering command opcode 8 CARD64 mask SeparableFilter2DPBO 2 44 rendering command length 2 327 rendering command opcode 8 CARD64 row 8 CARD64 column 4 ENUM target 4 ENUM internalFormat 4 CARD32 width 4 CARD32 height 4 ENUM apiFormat 4 ENUM apiType TexImage1DPBO 2 40 rendering command length 2 328 rendering command opcode 8 CARD64 image 4 ENUM target 4 CARD32 level 4 CARD32 components 4 CARD32 width 4 CARD32 border 4 ENUM apiFormat 4 ENUM apiType TexImage2DPBO 2 44 rendering command length 2 329 rendering command opcode 8 CARD64 image 4 ENUM target 4 CARD32 level 4 CARD32 components 4 CARD32 width 4 CARD32 height 4 CARD32 border 4 ENUM apiFormat 4 ENUM apiType TexImage3DPBO 2 48 rendering command length 2 330 rendering command opcode 8 CARD64 image 4 ENUM target 4 CARD32 level 4 CARD32 components 4 CARD32 width 4 CARD32 height 4 CARD32 depth 4 CARD32 border 4 ENUM apiFormat 4 ENUM apiType TexSubImage1DPBO 2 36 rendering command length 2 331 rendering command opcode 8 CARD64 image 4 ENUM target 4 CARD32 level 4 CARD32 xoffset 4 CARD32 width 4 ENUM apiFormat 4 ENUM apiType TexSubImage2DPBO 2 44 rendering command length 2 332 rendering command opcode 8 CARD64 image 4 ENUM target 4 CARD32 level 4 CARD32 xoffset 4 CARD32 yoffset 4 CARD32 width 4 CARD32 height 4 ENUM apiFormat 4 ENUM apiType TexSubImage3DPBO 2 52 rendering command length 2 333 rendering command opcode 8 CARD64 image 4 ENUM target 4 CARD32 level 4 CARD32 xoffset 4 CARD32 yoffset 4 CARD32 zoffset 4 CARD32 width 4 CARD32 height 4 CARD32 depth 4 ENUM apiFormat 4 ENUM apiType GetColorTablePBO 2 24 rendering command length 2 334 rendering command opcode 8 CARD64 table 4 ENUM target 4 ENUM apiFormat 4 ENUM apiType GetCompressedTexImagePBO 2 20 rendering command length 2 335 rendering command opcode 8 CARD64 img 4 ENUM target 4 CARD32 lod GetConvolutionFilterPBO 2 24 rendering command length 2 336 rendering command opcode 8 CARD64 image 4 ENUM target 4 ENUM apiFormat 4 ENUM apiType GetHistogramPBO 2 28 rendering command length 2 337 rendering command opcode 8 CARD64 values 4 ENUM target 4 ENUM apiFormat 4 ENUM apiType 1 BOOL reset 3 unused GetMinmaxPBO 2 28 rendering command length 2 338 rendering command opcode 8 CARD64 values 4 ENUM target 4 ENUM apiFormat 4 ENUM apiType 1 BOOL reset 3 unused GetPixelMapfvPBO 2 16 rendering command length 2 339 rendering command opcode 8 CARD64 values 4 ENUM map GetPixelMapuivPBO 2 16 rendering command length 2 340 rendering command opcode 8 CARD64 values 4 ENUM map GetPixelMapusvPBO 2 16 rendering command length 2 341 rendering command opcode 8 CARD64 values 4 ENUM map GetPolygonStipplePBO 2 12 rendering command length 2 342 rendering command opcode 8 CARD64 mask GetSeparableFilterPBO 2 40 rendering command length 2 343 rendering command opcode 8 CARD64 row 8 CARD64 column 8 CARD64 span 4 ENUM target 4 ENUM apiFormat 4 ENUM apiType GetTexImagePBO 2 28 rendering command length 2 344 rendering command opcode 8 CARD64 texels 4 ENUM target 4 CARD32 level 4 ENUM apiFormat 4 ENUM apiType ReadPixelsPBO 2 36 rendering command length 2 345 rendering command opcode 8 CARD64 pixels 4 CARD32 x 4 CARD32 y 4 CARD32 width 4 CARD32 height 4 ENUM apiFormat 4 ENUM apiType Errors INVALID_ENUM is generated if the parameter of BindBuffer, BufferData, BufferSubData, MapBuffer, UnmapBuffer, GetBufferSubData, GetBufferParameteriv, or GetBufferPointerv is not one of ARRAY_BUFFER, ELEMENT_ARRAY_BUFFER, PIXEL_PACK_BUFFER_ARB, or PIXEL_UNPACK_BUFFER_ARB. INVALID_OPERATION is generated if Bitmap, ColorSubTable, ColorTable, CompressedTexImage1D, CompressedTexImage2D, CompressedTexImage3D, CompressedTexSubImage1D, CompressedTexSubImage2D, CompressedTexSubImage3D, ConvolutionFilter1D, ConvolutionFilter2D, DrawPixels, PixelMapfv, PixelMapuiv, PixelMapusv, PolygonStipple, SeparableFilter2D, TexImage1D, TexImage2D, TexImage3D, TexSubImage1D, TexSubImage2D, or TexSubImage3D would unpack (read) data from the currently bound PIXEL_UNPACK_BUFFER_ARB buffer object such that the memory reads required for the command would exceed the memory (data store) size of the buffer object. INVALID_OPERATION is generated if GetColorTable, GetCompressedTexImage, GetConvolutionFilter, GetHistogram, GetMinmax, GetPixelMapfv, GetPixelMapuiv, GetPixelMapusv, GetPolygonStipple, GetSeparableFilter, GetTexImage, or ReadPixels would pack (write) data to the currently bound PIXEL_PACK_BUFFER_ARB buffer object such that the memory writes required for the command would exceed the memory (data store) size of the buffer object. INVALID_OPERATION is generated by GetColorTable, GetConvolutionFilter, GetHistogram, GetMinmax, GetSeparableFilter, GetTexImage and ReadPixels if the current PIXEL_PACK_BUFFER_BINDING_ARB value is non-zero and the table/image/values/span/img/data parameter is not evenly divisible into the number of basic machine units needed to store in memory a datum indicated by the type parameter. INVALID_OPERATION is generated by ColorTable, ColorSubTable, ConvolutionFilter2D, ConvolutionFilter1D, SeparableFilter2D, TexImage1D, TexImage2D, TexImage3D, TexSubImage1D, TexSubImage2D, TexSubImage3D, and DrawPixels if the current PIXEL_UNPACK_BUFFER_BINDING_ARB value is non-zero and the data parameter is not evenly divisible into the number of basic machine units needed to store in memory a datum indicated by the type parameter. INVALID_OPERATION is generated by GetPixelMapfv if the current PIXEL_PACK_BUFFER_BINDING_ARB value is non-zero and the data parameter is not evenly divisible into the number of basic machine units needed to store in memory a float datum. INVALID_OPERATION is generated by GetPixelMapuiv if the current PIXEL_PACK_BUFFER_BINDING_ARB value is non-zero and the data parameter is not evenly divisible into the number of basic machine units needed to store in memory a uint datum. INVALID_OPERATION is generated by GetPixelMapusv if the current PIXEL_PACK_BUFFER_BINDING_ARB value is non-zero and the data parameter is not evenly divisible into the number of basic machine units needed to store in memory a ushort datum. INVALID_OPERATION is generated by PixelMapfv if the current PIXEL_UNPACK_BUFFER_BINDING_ARB value is non-zero and the data parameter is not evenly divisible into the number of basic machine units needed to store in memory a float datum. INVALID_OPERATION is generated by PixelMapuiv if the current PIXEL_UNPACK_BUFFER_BINDING_ARB value is non-zero and the data parameter is not evenly divisible into the number of basic machine units needed to store in memory a uint datum. INVALID_OPERATION is generated by PixelMapusv if the current PIXEL_UNPACK_BUFFER_BINDING_ARB value is non-zero and the data parameter is not evenly divisible into the number of basic machine units needed to store in memory a ushort datum. Dependencies on EXT_pixel_buffer_object When this extension is supported, the EXT_pixel_buffer_object functionality adopts the tighter alignment and buffer bounds overflow error generation behavior of ARB_pixel_buffer_object (previously, EXT_pixel_buffer_object was not explicit about what happened in these situations). This is because the two extensions share the same enumerants. Dependencies on NV_pixel_data_range A non-zero pixel pack buffer binding takes priority over the READ_PIXEL_DATA_RANGE_NV enable. A non-zero pixel unpack buffer binding takes priority over the WRITE_PIXEL_DATA_RANGE_NV enable. New State (table 6.20, Pixels, p. 235) Initial Get Value Type Get Command Value Sec Attribute ------------------------------- ---- ----------- ------- ------ ----------- PIXEL_PACK_BUFFER_BINDING_ARB Z+ GetIntegerv 0 4.3.5 pixel-store PIXEL_UNPACK_BUFFER_BINDING_ARB Z+ GetIntegerv 0 6.1.13 pixel-store New Implementation Dependent State (none) Usage Examples Convenient macro definition for specifying buffer offsets: #define BUFFER_OFFSET(i) ((char *)NULL + (i)) Example 1: Render to vertex array: const int numberVertices = 100; // Create a buffer object for a number of vertices consisting of // 4 float values per vertex glGenBuffers(1, vertexBuffer); glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, vertexBuffer); glBufferData(GL_PIXEL_PACK_BUFFER_ARB, numberVertices*4, NULL, GL_DYNAMIC_DRAW); // Render vertex data into 100x1 strip of framebuffer using a // fragment program glBindProgram(FRAGMENT_PROGRAM_ARB, fragmentProgram); glDrawBuffer(GL_BACK); renderVertexData(); glBindProgramARB(FRAGMENT_PROGRAM_ARB, 0); // Read the vertex data back from framebuffer glReadBuffer(GL_BACK); glReadPixels(0, 0, numberVertices, 1, GL_BGRA, GL_FLOAT, BUFFER_OFFSET(0)); // Change the binding point of the buffer object to // the vertex array binding point glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer); glEnableClientState(VERTEX_ARRAY); glVertexPointer(4, GL_FLOAT, 0, BUFFER_OFFSET(0)); glDrawArrays(TRIANGLE_STRIP, 0, numberVertices); Example 2: Streaming textures Streaming textures using NV_pixel_data_range: const int texWidth = 256; const int texHeight = 256; const int texsize = texWidth * texHeight * 4; void *pdrMemory, *texData; pdrMemory = glAllocateMemoryNV(texsize, 0.0, 1.0, 1.0); glPixelDataRangeNV(GL_WRITE_PIXEL_DATA_RANGE_NV, texsize, pdrMemory); glEnableClientState(GL_WRITE_PIXEL_DATA_RANGE_NV); // Define texture level (without an image) glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, texWidth, texHeight, 0, GL_BGRA, GL_UNSIGNED_BYTE, NULL); // Setup texture environment ... texData = getNextImage(); while (texData) { memcpy(pdrMemory, texData, texsize); glFlushPixelDataRangeNV(GL_WRITE_PIXEL_DATA_RANGE_NV); glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, texWidth, texHeight, GL_BGRA, GL_UNSIGNED_BYTE, pdrMemory); // Draw textured geometry glBegin(GL_QUADS); ... glEnd(); texData = getNextImage(); } glDisableClientState(GL_WRITE_PIXEL_DATA_RANGE_NV); glFreeMemoryNV(pdrMemory); Streaming textures using pixel buffer objects: const int texWidth = 256; const int texHeight = 256; const int texsize = texWidth * texHeight * 4; void *pboMemory, *texData; // Define texture level zero (without an image); notice the // explicit bind to the zero pixel unpack buffer object so that // pass NULL for the image data leaves the texture image // unspecified. glBindBuffer(GL_PIXEL_UNPACK_BUFFER_ARB, 0); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, texWidth, texHeight, 0, GL_BGRA, GL_UNSIGNED_BYTE, NULL); // Create and bind texture image buffer object glGenBuffers(1, &texBuffer); glBindBuffer(GL_PIXEL_UNPACK_BUFFER_ARB, texBuffer); // Setup texture environment ... texData = getNextImage(); while (texData) { // Reset the contents of the texSize-sized buffer object glBufferData(GL_PIXEL_UNPACK_BUFFER_ARB, texSize, NULL, GL_STREAM_DRAW); // Map the texture image buffer (the contents of which // are undefined due to the previous glBufferData) pboMemory = glMapBuffer(GL_PIXEL_UNPACK_BUFFER_ARB, GL_WRITE_ONLY); // Modify (sub-)buffer data memcpy(pboMemory, texData, texsize); // Unmap the texture image buffer glUnmapBuffer(GL_PIXEL_UNPACK_BUFFER_ARB); // Update (sub-)teximage from texture image buffer glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, texWidth, texHeight, GL_BGRA, GL_UNSIGNED_BYTE, BUFFER_OFFSET(0)); // Draw textured geometry glBegin(GL_QUADS); ... glEnd(); texData = getNextImage(); } glBindBuffer(GL_PIXEL_UNPACK_BUFFER_ARB, 0); Example 3: Asynchronous glReadPixels Traditional glReadPixels: const int imagewidth = 640; const int imageheight = 480; GLubyte readBuffer[imagewidth*imageheight*4]; // Render to framebuffer glDrawBuffer(GL_BACK); renderScene() // Read image from framebuffer glReadBuffer(GL_BACK); glReadPixels(0, 0, imagewidth, imageheight, GL_BGRA, GL_UNSIGNED_BYTE, readBuffer); // Process image when glReadPixels returns after reading the // whole buffer processImage(readBuffer); Asynchronous glReadPixels: const int imagewidth = 640; const int imageheight = 480; const int imageSize = imagewidth*imageheight*4; glGenBuffers(2, imageBuffers); glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, imageBuffers[0]); glBufferData(GL_PIXEL_PACK_BUFFER_ARB, imageSize / 2, NULL, GL_STREAM_READ); glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, imageBuffers[1]); glBufferData(GL_PIXEL_PACK_BUFFER_ARB, imageSize / 2, NULL, GL_STREAM_READ); // Render to framebuffer glDrawBuffer(GL_BACK); renderScene(); // Bind two different buffer objects and start the glReadPixels // asynchronously. Each call will return directly after // starting the DMA transfer. glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, imageBuffers[0]); glReadPixels(0, 0, imagewidth, imageheight/2, GL_BGRA, GL_UNSIGNED_BYTE, BUFFER_OFFSET(0)); glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, imageBuffers[1]); glReadPixels(0, imageheight/2, imagewidth, imageheight/2, GL_BGRA, GL_UNSIGNED_BYTE, BUFFER_OFFSET(0)); // Process partial images. Mapping the buffer waits for // outstanding DMA transfers into the buffer to finish. glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, imageBuffers[0]); pboMemory1 = glMapBuffer(GL_PIXEL_PACK_BUFFER_ARB, GL_READ_ONLY); processImage(pboMemory1); glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, imageBuffers[1]); pboMemory2 = glMapBuffer(GL_PIXEL_PACK_BUFFER_ARB, GL_READ_ONLY); processImage(pboMemory2); // Unmap the image buffers glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, imageBuffers[0]); glUnmapBuffer(GL_PIXEL_PACK_BUFFER_ARB); glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, imageBuffers[1]); glUnmapBuffer(GL_PIXEL_PACK_BUFFER_ARB); Appendix on Pack/Unpack Range The complexity of OpenGL's pixel pack/unpack state makes it difficult to express succinctly what range of a pixel buffer object will be accessed by a pixel command. The following code, following the conventions of the SGI OpenGL Sample Implementation, returns the limit (one byte more than the maximum allowed offset into the buffer object) for the memory a pixel command will read/write. /* ** Compute offset limit into user's data considering all pixel ** store modes. This offset limit is ONE MORE than the largest byte ** offset for the image. */ static GLsizeiptr OffsetLimitImage3D(__GLpixelStoreMode *pixelStoreMode, GLsizei width, GLsizei height, GLsizei depth, GLenum format, GLenum type, const void *userdata, GLint skip_images) { const GLint line_length = pixelStoreMode->lineLength; const GLint image_height = pixelStoreMode->imageHeight; const GLint alignment = pixelStoreMode->alignment; const GLint skip_pixels = pixelStoreMode->skipPixels; const GLint skip_lines = pixelStoreMode->skipLines; GLsizeiptr offsetLimit = (GLsizeiptr) userdata; GLint rowsize; GLint padding; GLint imagesize; assert(width > 0); assert(height > 0); assert(depth > 0); assert(line_length >= 0); assert(image_height >= 0); assert(skip_pixels >= 0); assert(skip_lines >= 0); assert(skip_images >= 0); assert((alignment == 1) || (alignment == 2) || (alignment == 4) || (alignment == 8)); /* All formats except GL_BITMAP fall out trivially */ if (type == GL_BITMAP) { const GLint groups_per_line = (line_length > 0) ? line_length : width; const GLint rows_per_image = (image_height > 0) ? image_height : height; assert(1 == __glElementsPerGroup(format, type)); rowsize = (groups_per_line + 7) / 8; padding = rowsize & (alignment-1); if (padding) { rowsize += alignment - padding; } imagesize = rows_per_image * rowsize; offsetLimit += imagesize * (skip_images + depth-1); offsetLimit += rowsize * (skip_lines + height-1); offsetLimit += (skip_pixels + width+7)/8; } else { const GLint components = __glElementsPerGroup(format, type); const GLint element_size = __glBytesPerElement(type); const GLint group_size = element_size * components; if (0 == (line_length | image_height | skip_pixels | skip_lines | skip_pixels)) { // Fast path: when above pixel store modes are all zero. rowsize = width * group_size; // Default alignment is 4 so allow arbitrary alignment // on fast path. padding = rowsize & (alignment-1); if (padding) { rowsize += alignment - padding; } imagesize = depth * height * rowsize; offsetLimit += imagesize; } else { // General path: when one or more non-zero pixel store modes. const GLint groups_per_line = (line_length > 0) ? line_length : width; const GLint rows_per_image = (image_height > 0) ? image_height : height; rowsize = groups_per_line * group_size; padding = rowsize & (alignment-1); if (padding) { rowsize += alignment - padding; } imagesize = rows_per_image * rowsize; offsetLimit += imagesize * (skip_images + depth-1); offsetLimit += rowsize * (skip_lines + height-1); offsetLimit += group_size * (skip_pixels + width); } } return offsetLimit; } GLsizeiptr __glOffsetLimitImage3D(__GLpixelStoreMode *pixelStoreMode, GLsizei width, GLsizei height, GLsizei depth, GLenum format, GLenum type, const void *userdata) { return OffsetLimitImage3D(pixelStoreMode, width, height, depth, format, type, userdata, pixelStoreMode->skipImages); } GLsizeiptr __glOffsetLimitImage(__GLpixelStoreMode *pixelStoreMode, GLsizei width, GLsizei height, GLenum format, GLenum type, const void *userdata) { /* NOTE: Non-3D image max offset computations ignore (treat as zero) the unpackModes.skipImages state! */ return OffsetLimitImage3D(pixelStoreMode, width, height, 1, format, type, userdata, 0); // Treat skipImages as zero. } Revision History revision 0.3: mjk Numbered issues. Add issues 14 through 18. Remove all gl/GL prefix/suffixing in specification sections. Use gl/GL prefix/suffixing in sections other than the specification sections. Leaving off prefixes in non-specification sections is ambiguous, particularly within example source code. Base specification language updates on OpenGL 2.0 specification. Add buffer object required state section. Added GL_INVALID_OPERATION when an offset accessed (read or written) for a pixel command from/to a pixel buffer object would exceed the size of the buffer object. Added GL_INVALID_OPERATION when for misaligned offsets. Added "Appendix on Pack/Unpack Range". Add GLX protocol discussion. revision 0.4: mjk Fixed grammar issues from Brian Paul. Improved example code and fixed grammar from Nick Carter. Explain how a NULL data parameter to glTexImage commands works. revision 0.5: mjk Clarify that glBufferData usage modes apply to drawing _and_ image specification commands. revision 0.6: mjk Add "streaming draw pixels" to the list of interesting approaches for this extension in the Overview. Add issue discussing the relationship of this extension to data aquisition hardware. revision 0.7: mjk Assign enumerant values to match the EXT_pixel_buffer_object values. Add issue explaining why the ARB extension shares enums with EXT_pixel_buffer_object. Apply Dale's suggestion to improve the clarity of the usage pattern parameters to glBufferData. revision 0.8 mjk Typo fixes from Ian Romanick and Nick Carter. revision 1.0 mjk Add issue 23 for Jeremy about render-to-vertex-array. Move render-to-vertex-array justification in overview to bottom of the list. revision 1.1 srahman Add GLX protocol support. revision 1.2 Jon Leech Change GLvoid -> void (Bug 10412).