| Name |
| |
| IMG_texture_compression_pvrtc |
| |
| Name Strings |
| |
| GL_IMG_texture_compression_pvrtc |
| |
| Notice |
| |
| Copyright Imagination Technologies Limited, 2005. |
| |
| Contact |
| |
| Graham Connor, Imagination Technologies (graham 'dot' connor 'at' |
| imgtec 'dot' com) |
| |
| Status |
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| Complete |
| |
| Version |
| |
| 1.3, 20 September 2012 |
| |
| Number |
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| OpenGL ES Extension #54 |
| |
| Dependencies |
| |
| This extension is written against the OpenGL ES 1.0 Specification, (which in turn |
| is derived from OpenGL 1.3). Thus this spec is effectively written against OpenGL |
| 1.3 but does not address sections explicitly removed or reduced by OpenGL ES 1.0. |
| It can be implemented against OpenGL ES 2.0. |
| |
| OpenGL ES 2.0 affects the definition of this extension. |
| |
| APPLE_texture_2D_limited_npot affects the definition of this extension. |
| |
| Overview |
| |
| This extension provides additional texture compression functionality |
| specific to Imagination Technologies PowerVR Texture compression format |
| (called PVRTC) subject to all the requirements and limitations described |
| by the OpenGL 1.3 specifications. |
| |
| This extension supports 4 and 2 bit per pixel texture compression |
| formats. Because the compression of PVRTC is very CPU intensive, |
| it is not appropriate to carry out compression on the target |
| platform. Therefore this extension only supports the loading of |
| compressed texture data. |
| |
| IP Status |
| |
| Imagination Technologies Proprietary |
| |
| Issues |
| |
| 1) Different versions of PowerVR hardware may interpret the |
| compression formats differently. |
| |
| Resolution: If this situation arises, or could potentially arise |
| in the field, then further extensions would be defined to add tokens |
| for these compression formats. |
| |
| 2) Future revisions of PowerVR hardware might allow custom |
| texture dimensions to be used. How will this be dealt with? |
| |
| Resolution: As with Issue 1, further extensions would be defined to |
| add tokens for extra compression formats. |
| |
| 3) PVRTC can encode alpha and opaque data in the same image and |
| this is handled seamlessly by the hardware decode. Why then are |
| there separate tokens for RGB and RGBA compressed textures? |
| |
| Resolution: OpenGL needs to know whether a texture contains |
| alpha data so that the blend modes can be set up correctly. If |
| this information is not encoded in the image format token then |
| some blends will be unobtainable. Note that the driver scanning |
| the data is not a viable solution as it would restrict a |
| texture to being used in one mode only. |
| |
| 4) If this extension does not support driver compression of data, |
| how is data compressed? |
| |
| Resolution: Textures should be compressed using the |
| PVRTextureTool available from PowerVR Developer Relations |
| (devrel 'at' powervr 'dot' com) |
| |
| 5) Is sub-texturing supported? |
| |
| Resolution: Only for the reloading of complete |
| images. Sub-images are not supportable because the PVRTC |
| algorithm uses significant adjacency information, so there is |
| no discrete block of texels that can be decoded as a standalone |
| sub-unit, and so it follows that no stand alone sub-unit of |
| data can be loaded without changing the decoding of surrounding |
| texels. |
| |
| 6) How is the imageSize argument calculated for the CompressedTexImage2D |
| and CompressedTexSubImage2D functions. |
| |
| Resolution: For PVRTC 4BPP formats the imageSize is calculated as: |
| ( max(width, 8) * max(height, 8) * 4 + 7) / 8 |
| For PVRTC 2BPP formats the imageSize is calculated as: |
| ( max(width, 16) * max(height, 8) * 2 + 7) / 8 |
| |
| New Procedures and Functions |
| |
| None. |
| |
| New Tokens |
| |
| Accepted by the <internalformat> parameter of CompressedTexImage2D |
| and the <format> parameter of CompressedTexSubImage2D: |
| |
| COMPRESSED_RGB_PVRTC_4BPPV1_IMG 0x8C00 |
| COMPRESSED_RGB_PVRTC_2BPPV1_IMG 0x8C01 |
| COMPRESSED_RGBA_PVRTC_4BPPV1_IMG 0x8C02 |
| COMPRESSED_RGBA_PVRTC_2BPPV1_IMG 0x8C03 |
| |
| Additions to Chapter 2 of the OpenGL 1.3 Specification (OpenGL Operation) |
| |
| None. |
| |
| Additions to Chapter 3 of the OpenGL 1.3 Specification (Rasterization) |
| |
| Add to Table 3.16.1: Specific Compressed Internal Formats |
| |
| Compressed Internal Format Base Internal Format |
| ========================== ==================== |
| COMPRESSED_RGB_PVRTC_4BPPV1_IMG RGB |
| COMPRESSED_RGB_PVRTC_2BPPV1_IMG RGB |
| COMPRESSED_RGBA_PVRTC_4BPPV1_IMG RGBA |
| COMPRESSED_RGBA_PVRTC_2BPPV1_IMG RGBA |
| |
| |
| Modify Section 3.8.3, Compressed Texture Images |
| |
| Add to Section 3.8.3, Compressed Texture Images (adding to the end of |
| the CompressedTexImage section) |
| |
| If <internalformat> is COMPRESSED_RGB_PVRTC_4BPPV1_IMG, |
| COMPRESSED_RGB_PVRTC_2BPPV1_IMG, COMPRESSED_RGBA_PVRTC_4BPPV1_IMG, or |
| COMPRESSED_RGBA_PVRTC_2BPPV1_IMG, the compressed texture is stored using one |
| of several PVRTC compressed texture image formats. The PVRTC texture |
| compression algorithm supports only 2D images without borders. |
| CompressedTexImage2D will produce an INVALID_VALUE if <border> is non-zero. |
| |
| Add to Section 3.8.3, Compressed Texture Images (adding to the end of |
| the CompressedTexSubImage section) |
| |
| If the internal format of the texture image being modified is |
| COMPRESSED_RGB_PVRTC_4BPPV1_IMG, COMPRESSED_RGB_PVRTC_2BPPV1_IMG, |
| COMPRESSED_RGBA_PVRTC_4BPPV1_IMG, or COMPRESSED_RGBA_PVRTC_2BPPV1_IMG the |
| texture is stored using one of the several PVRTC compressed texture image |
| formats. CompressedTexSubImage2D result in an INVALID_OPERATION error only |
| if one of the following conditions occurs: |
| |
| * <width> is not equal to TEXTURE_WIDTH. |
| * <height> is not equal to TEXTURE_HEIGHT. |
| * <xoffset> or <yoffset> is not zero. |
| |
| |
| Additions to Chapter 4 of the OpenGL 1.3 Specification (Per-Fragment |
| Operations and the Frame Buffer) |
| |
| None. |
| |
| Additions to Chapter 5 of the OpenGL 1.3 Specification (Special Functions) |
| |
| None. |
| |
| Additions to Chapter 6 of the OpenGL 1.3 Specification (State and |
| State Requests) |
| |
| None. |
| |
| Additions to Appendix A of the OpenGL 1.3 Specification (Invariance) |
| |
| None. |
| |
| Additions to the AGL/GLX/WGL Specifications |
| |
| None. |
| |
| GLX Protocol |
| |
| None. |
| |
| Interactions with OpenGL ES 2.0 and APPLE_texture_2D_limited_npot |
| |
| If the GL is OpenGL ES 2.0 or if APPLE_texture_2D_limited_npot is |
| supported, either of which introduces general support for non-power-of-two |
| texture dimensions, the error condition from OpenGL ES 1.1 restricting |
| NPOT dimensions is reintroduced specifically for CompressedTexImage2D when |
| <internalformat> is one of the PVRTC formats: |
| |
| "For non-zero <width> and <height>, it must be the case that |
| |
| w_s = 2^n (3.12) |
| h_s = 2^m (3.13) |
| |
| for some integers n and m, where w_s and h_s are the specified image width |
| and height. If any one of these relationships cannot be satisfied, then |
| the error INVALID_VALUE is generated." |
| |
| Errors |
| |
| INVALID_VALUE is generated by CompressedTexImage2D if |
| <internalformat> is COMPRESSED_RGB_PVRTC_4BPPV1_IMG, |
| COMPRESSED_RGB_PVRTC_2BPPV1_IMG, COMPRESSED_RGBA_PVRTC_4BPPV1_IMG, or |
| COMPRESSED_RGBA_PVRTC_2BPPV1_IMG and <border> is not equal to zero. |
| |
| INVALID_OPERATION is generated by CompressedTexSubImage2D if INTERNAL_FORMAT |
| is COMPRESSED_RGB_PVRTC_4BPPV1_IMG, COMPRESSED_RGB_PVRTC_2BPPV1_IMG, |
| COMPRESSED_RGBA_PVRTC_4BPPV1_IMG, or COMPRESSED_RGBA_PVRTC_2BPPV1_IMG |
| and any of the following apply: <width> is not equal to TEXTURE_WIDTH; |
| <height> is not equal to TEXTURE_HEIGHT; <xoffset> and <yoffset> are not zero. |
| |
| New State |
| |
| None. |
| |
| Revision History |
| |
| 0.1, 18/12/2003 gdc: Initial revision. |
| 0.2, 13/01/2004 gdc: Formatting changes. |
| 0.3, 24/08/2004 gdc: Mini-mip behaviour. |
| 0.4, 25/01/2005 nt: Removed sections about CompressedTex[Sub]Image[1|3]D |
| and rewrote specs based on OpenGL 1.3. |
| 1.0, 30/04/2009 bcb: Final cleanup for publish to the registry |
| 1.1, 01/11/2011 bcb: Fix some incorrect error conditions (not matching |
| reality) |
| 1.2, 08/05/2012 bnl: Fix missing error for NPOT dimensions and remove |
| occasional use of ARB suffixes |
| 1.3, 20/09/2012 bcb: Remove 1:1 language to match error conditions |
| |
