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kc3-lang/angle/extensions/EXT_texture_rg.txt
Geoff Lang
- extensions/EXT_texture_rg.txt
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Name EXT_texture_rg Name Strings GL_EXT_texture_rg Contributors Contributors to ARB_texture_rg, on which this extension is based Kyle Haughey Richard Schreyer Contact Benj Lipchak, Apple (lipchak 'at' apple.com) Status Complete Version Date: July 22, 2011 Revision: 3 Number OpenGL ES Extension #103 Dependencies Requires OpenGL ES 2.0. Written based on the wording of the OpenGL ES 2.0.25 Full Specification (November 2, 2010). OES_texture_float affects the definition of this extension. OES_texture_half_float affects the definition of this extension. APPLE_framebuffer_multisample affects the definition of this extension. Overview Historically one- and two-component textures have been specified in OpenGL ES using the luminance or luminance-alpha (L/LA) formats. With the advent of programmable shaders and render-to-texture capabilities these legacy formats carry some historical artifacts which are no longer useful. For example, when sampling from such textures, the luminance values are replicated across the color components. This is no longer necessary with programmable shaders. It is also desirable to be able to render to one- and two-component format textures using capabilities such as framebuffer objects (FBO), but rendering to L/LA formats is under-specified (specifically how to map R/G/B/A values to L/A texture channels). This extension adds new base internal formats for one-component RED and two-component RG (red green) textures as well as sized RED and RG internal formats for renderbuffers. The RED and RG texture formats can be used for both texturing and rendering into with framebuffer objects. New Procedures and Functions None New Tokens Accepted by the <internalformat> parameter of TexImage2D and CopyTexImage2D, and the <format> parameter of TexImage2D, TexSubImage2D, and ReadPixels: RED_EXT 0x1903 RG_EXT 0x8227 Accepted by the <internalformat> parameter of RenderbufferStorage and RenderbufferStorageMultisampleAPPLE: R8_EXT 0x8229 RG8_EXT 0x822B Additions to Chapter 2 of the OpenGL ES 2.0 Specification (OpenGL ES Operation) None Additions to Chapter 3 of the OpenGL ES 2.0 Specification (Rasterization) (Add the following to Table 3.3: "TexImage2D and ReadPixels formats") Format Name Element Meaning and Order Target Buffer ----------- ------------------------- ------------- RED_EXT R Color RG_EXT R, G Color (Add the following to Table 3.4: "Valid pixel format and type combinations") (as modified by OES_texture_float and OES_texture_half_float) Format Type Bytes per Pixel ----------- ------------------------- --------------- RED_EXT FLOAT 4 RED_EXT HALF_FLOAT_OES 2 RED_EXT UNSIGNED_BYTE 1 RG_EXT FLOAT 8 RG_EXT HALF_FLOAT_OES 4 RG_EXT UNSIGNED_BYTE 2 (Add the following to Table 3.8: "Conversion from RGBA and depth pixel components to internal texture") Base Internal Format RGBA Internal Components -------------------- ------ ------------------- RED_EXT R R RG_EXT R,G R,G (Modify Table 3.9: "CopyTexImage internal format/color buffer combinations") Texture Format Color Buffer A L LA R RG RGB RGBA ------------ - - -- - -- --- ---- A X R X X RG X X X RGB X X X X RGBA X X X X X X X (Add the following to Table 3.12: "Correspondence of filtered texture components to texture source color components") Texture Base Texture source color Internal Format C_s A_s --------------- ------------- ------ RED_EXT (R_t, 0, 0) 1 RG_EXT (R_t, G_t, 0) 1 Additions to Chapter 4 of the OpenGL ES 2.0 Specification (Per-Fragment Operations and the Framebuffer) In section 4.3.1 "Reading Pixels", subsection "Obtaining Pixels from the Framebuffer", modify the last sentence to read: "If the framebuffer does not support G, B, or A values then the G, B, and A values that are obtained are 0.0, 0.0, and 1.0 respectively." In section 4.4.5 "Framebuffer Completeness", modify the last sentence of the second paragraph to read: "Color-renderable formats contain red, and possibly green, blue, and alpha components; depth-renderable formats contain depth components; and stencil-renderable formats contain stencil components." (Add the following to Table 4.5: "Renderbuffer image formats, showing their renderable type (color-, depth-, or stencil-renderable) and the number of bits each format contains for color (R, G, B, A), depth (D), and stencil (S) components") Sized Internal Renderable Type R bits G bits B bits A bits D bits S bits Format -------------- ---------------- ------ ------ ------ ------ ------ ------ R8_EXT color-renderable 8 RG8_EXT color-renderable 8 8 Additions to Chapter 5 of the OpenGL ES 2.0 Specification (Special Functions) None Additions to Chapter 6 of the OpenGL ES 2.0 Specification (State and State Requests) None Dependencies on OES_texture_float If OES_texture_float is not supported, then omit the rows of Table 3.4 that have Type FLOAT. Dependencies on OES_texture_half_float If OES_texture_half_float is not supported, then omit the rows of Table 3.4 that have Type HALF_FLOAT_OES. Dependencies on APPLE_framebuffer_multisample If APPLE_framebuffer_multisample is not supported, then all references to RenderbufferStorageMultisampleAPPLE should be ignored. Revision History #1 February 22, 2011, khaughey - initial version adapted from ARB_texture_rg. #2 June 16, 2011, benj - add interaction with APPLE_framebuffer_multisample #3 July 22, 2011, benj - rename from APPLE to EXT