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138 lines
3.6 KiB
138 lines
3.6 KiB
Name |
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MESA_pack_invert |
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Name Strings |
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GL_MESA_pack_invert |
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Contact |
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Brian Paul, Tungsten Graphics, Inc. (brian.paul 'at' tungstengraphics.com) |
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Keith Whitwell, Tungsten Graphics, Inc. (keith 'at' tungstengraphics.com) |
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Status |
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Shipping (Mesa 4.0.4 and later) |
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Version |
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1.0 |
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Number |
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TBD |
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Dependencies |
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OpenGL 1.0 or later is required |
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This extensions is written against the OpenGL 1.4 Specification. |
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Overview |
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This extension adds a new pixel storage parameter to indicate that |
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images are to be packed in top-to-bottom order instead of OpenGL's |
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conventional bottom-to-top order. Only pixel packing can be |
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inverted (i.e. for glReadPixels, glGetTexImage, glGetConvolutionFilter, |
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etc). |
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Almost all known image file formats store images in top-to-bottom |
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order. As it is, OpenGL reads images from the frame buffer in |
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bottom-to-top order. Thus, images usually have to be inverted before |
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writing them to a file with image I/O libraries. This extension |
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allows images to be read such that inverting isn't needed. |
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IP Status |
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None |
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Issues |
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1. Should we also define UNPACK_INVERT_MESA for glDrawPixels, etc? |
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Resolved: No, we're only concerned with pixel packing. There are other |
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solutions for inverting images when using glDrawPixels (negative Y pixel |
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zoom) or glTexImage (invert the vertex T coordinates). It would be easy |
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enough to define a complementary extension for pixel packing in the |
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future if needed. |
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New Procedures and Functions |
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None |
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New Tokens |
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Accepted by the <pname> parameter of PixelStorei and PixelStoref |
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and the <pname> parameter of GetIntegerv, GetFloatv, GetDoublev |
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and GetBooleanv: |
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PACK_INVERT_MESA 0x8758 |
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Additions to Chapter 2 of the OpenGL 1.4 Specification (OpenGL Operation) |
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None |
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Additions to Chapter 3 of the OpenGL 1.4 Specification (Rasterization) |
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None |
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Additions to Chapter 4 of the OpenGL 1.4 Specification (Per-Fragment |
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Operations and the Frame Buffer) |
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Add the following entry to table 4.4 (PixelStore parameters) on page 182: |
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Parameter Name Type Initial Value Valid Range |
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--------------------------------------------------------- |
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PACK_INVERT_MESA boolean FALSE TRUE/FALSE |
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In the section labeled "Placement in Client Memory" on page 184 |
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insert the following text into the paragraph before the sentence |
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that starts with "If the format is RED, GREEN, BLUE...": |
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"The parameter PACK_INVERT_MESA controls whether the image is packed |
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in bottom-to-top order (the default) or top-to-bottom order. Equation |
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3.8 is modified as follows: |
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... the first element of the Nth row is indicated by |
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p + Nk, if PACK_INVERT_MESA is false |
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p + k * (H - 1) - Nk, if PACK_INVERT_MESA is true, where H is the |
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image height |
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" |
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Additions to Chapter 5 of the OpenGL 1.4 Specification (Special Functions) |
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None |
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Additions to Chapter 6 of the OpenGL 1.4 Specification (State and |
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State Requests) |
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None |
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Additions to Appendix A of the OpenGL 1.4 Specification (Invariance) |
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None |
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Additions to the AGL/GLX/WGL Specifications |
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None |
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GLX Protocol |
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None |
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Errors |
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None |
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New State |
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Add the following entry to table 6.20 (Pixels) on page 235: |
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Get Value Type Get Cmd Initial Value Description Sec Attribute |
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-------------------------------------------------------------------------------------------------- |
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PACK_INVERT_MESA boolean GetBoolean FALSE Value of PACK_INVERT_MESA 4.3.2 pixel-store |
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Revision History |
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21 September 2002 - Initial draft
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