| Name |
| |
| EXT_render_snorm |
| |
| Name Strings |
| |
| GL_EXT_render_snorm |
| |
| Contributors |
| |
| Daniel Koch, NVIDIA |
| Jan-Harald Fredriksen, ARM |
| Mathias Heyer, NVIDIA |
| |
| Contact |
| |
| Mathias Heyer, NVIDIA (mheyer [at] nvidia.com) |
| |
| Status |
| |
| Complete |
| |
| Version |
| |
| Last Modified Date: 2014-10-24 |
| Revision: 4 |
| |
| Number |
| |
| OpenGL ES Extension #206 |
| |
| Dependencies |
| |
| OpenGL ES 3.1 is required. |
| |
| This extension is written against the OpenGL ES 3.1 (June 4, 2014) |
| specification. |
| |
| This extension interacts with EXT_texture_norm16. |
| |
| Overview |
| |
| OpenGL ES 3.1 supports a variety of signed normalized texture and |
| renderbuffer formats which are not color-renderable. |
| |
| This extension enables signed normalized texture and renderbuffer |
| formats to be color-renderable. |
| |
| New Procedures and Functions |
| |
| None |
| |
| New Tokens |
| |
| Accepted by the <type> parameter of ReadPixels |
| |
| BYTE 0x1400 // core OpenGL ES 3.1 |
| SHORT 0x1402 // core OpenGL ES 3.1 |
| |
| Accepted by the <internalFormat> parameter of RenderbufferStorage |
| and RenderbufferStorageMultisample: |
| |
| R8_SNORM 0x8F94 // core OpenGL ES 3.1 |
| RG8_SNORM 0x8F95 // core OpenGL ES 3.1 |
| RGBA8_SNORM 0x8F97 // core OpenGL ES 3.1 |
| R16_SNORM_EXT 0x8F98 // EXT_texture_norm16 |
| RG16_SNORM_EXT 0x8F99 // EXT_texture_norm16 |
| RGBA16_SNORM_EXT 0x8F9B // EXT_texture_norm16 |
| |
| Additions to Chapter 8 of the OpenGL ES 3.1 Specification |
| (Textures and Samplers) |
| |
| Changes to Section 8.6 "Alternate Texture ImageSpecification Commands": |
| |
| Modify INVALID_OPERATION errors section on CopyTexImage2D, |
| first bullet point from: |
| |
| "if signed integer, unsigned integer, or fixed-point RGBA data is |
| required and the format of the current color buffer does not match |
| the required format." |
| |
| to |
| |
| "if FRAMEBUFFER_ATTACHMENT_COMPONENT_TYPE for the framebuffer |
| attachment corresponding to the read buffer does not match |
| the component type of the requested <internalformat>." |
| |
| |
| Change Table 8.13 "Correspondence of sized internal formats to base |
| internal formats,...": |
| |
| Sized Base Bits/component CR TF Req. Req. |
| Internal Internal S are shared bits rend. tex. |
| Format Format R G B A S |
| ------------ ----------- ---- ---- ---- --- ---- --- --- ---- --- |
| R8_SNORM RED s8 X X X X |
| RG8_SNORM RG s8 s8 X X X X |
| RGBA8_SNORM RGBA s8 s8 s8 s8 X X X X |
| R16_SNORM_EXT RED s16 X X X X |
| RG16_SNORM_EXT RG s16 s16 X X X X |
| RGBA16_SNORM_EXT RGBA s16 s16 s16 s16 X X X X |
| |
| Change Table 8.15: "ReadPixels format and type used during CopyTex*." |
| |
| Replace the first row with the following: |
| |
| Read Buffer Format format type |
| ------------------------------------ ------ ------------- |
| 8bit Unsigned Normalized Fixed-point RGBA UNSIGNED_BYTE |
| 8bit Signed Normalized Fixed-point RGBA BYTE |
| 16bit Signed Normalized Fixed-point RGBA SHORT |
| |
| |
| Additions to Chapter 15 of the OpenGL ES 3.1 Specification |
| (Writing Fragments and Samples to the Framebuffer) |
| |
| Changes to Section 15.1.7 "Blending": |
| |
| Replace |
| |
| "The components of the source and destination values and blend |
| factors are clamped to [0, 1] prior to evaluating the blend |
| equation." |
| |
| with |
| |
| "If the color buffer is fixed-point, the components of the |
| source and destination values and blend factors are each clamped |
| to [0, 1] or [-1, 1] respectively for an unsigned normalized or |
| signed normalized color buffer prior to evaluating the blend |
| equation." |
| |
| Changes to Section 15.1.7.1 "Blend Equation": |
| |
| Replace |
| |
| "Unsigned normalized fixed-point destination (framebuffer) |
| components are represented as described in section 2.3.4." |
| |
| with |
| |
| "Normalized fixed-point destination (framebuffer) components are |
| represented as described in section 2.3.4." |
| |
| Replace |
| |
| "Prior to blending, unsigned normalized fixed-point color |
| components undergo an implied conversion to floating-point using |
| equation 2.1." |
| |
| with |
| |
| "Prior to blending, unsigned and signed normalized fixed-point |
| color components undergo an implied conversion to floating-point |
| using equation 2.1 and 2.2, respectively." |
| |
| Changes to Section 15.1.7.3 "Blend Color" |
| |
| Replace |
| |
| "If destination framebuffer components use an unsigned |
| normalized fixed-point representation, the constant color |
| components are clamped to the range [0, 1] when computing blend |
| factors." |
| |
| with |
| |
| "If destination framebuffer components use an unsigned or |
| signed normalized fixed-point representation, the constant color |
| components are clamped to the range [0, 1] or [-1, 1], |
| respectively, when computing blend factors." |
| |
| Changes to Section 15.2.3 "Clearing the Buffers": |
| |
| Replace |
| |
| "Unsigned normalized fixed-point RGBA color buffers are cleared |
| to color values derived by clamping each component of the clear |
| color to the range [0, 1], then converting the (possibly sRGB |
| converted and/or dithered) color to fixed-point using equations |
| 2.3 or 2.4, respectively." |
| |
| with |
| |
| "Unsigned normalized fixed-point or signed normalized |
| fixed-point RGBA color buffers are cleared to color values |
| derived by clamping each component of the clear color to the |
| range [0, 1] or [-1, 1] respectively, then converting the |
| (possibly sRGB converted and/or dithered) color to fixed-point |
| using equations 2.3 or 2.4, respectively." |
| |
| Add to the second paragraph of Section 16.1.2 "ReadPixels": |
| |
| "For 8bit signed normalized fixed-point rendering surfaces, the |
| combination format RGBA and type BYTE is accepted. For a 16bit |
| signed normalized fixed point buffer, the combination RGBA and |
| SHORT is accepted." |
| |
| Add to Section 16.1.4 "Conversion of RGBA values": |
| |
| For signed normalized fixed-point color buffer, each element |
| is converted to floating-point using equation 2.2. |
| |
| |
| Errors |
| |
| No new errors. |
| |
| |
| Interactions with EXT_texture_norm16 |
| |
| If EXT_texture_norm16 is not supported, remove references to R16_SNORM_EXT, |
| RG16_SNORM_EXT, RGB16_SNORM_EXT, RGBA16_SNORM_EXT. Remove language and |
| additions referring to 16bit (signed / unsigned) normalized fixed |
| point buffers. |
| |
| |
| Issues |
| |
| 1. How does this extension differ from the functionality offered by GL4.4? |
| |
| On GL, the affected formats are generally exposed as 'color |
| renderable' but not as 'required renderbuffer format', which |
| might be interpreted as 'optionally renderable'. EXT_render_snorm |
| tries to avoid this ambiguity by introducing formats as 'neither |
| color-renderable nor req. renderbuffer format' or as |
| 'color-renderable plus required renderbuffer format', but not a |
| mixture of both. DX 10.1 level hardware is expected to supported |
| these formats as being renderable. 3-component snorm formats were |
| left out as they are not expected to map well to native hardware |
| formats. |
| |
| 2. Are format conversions between UNORM and SNORM formats allowed |
| for CopyTexImage2D? |
| |
| The OpenGL ES specs describe the CopyTexImage2D operation in |
| terms of ReadPixels followed by TexImage2D. The ReadPixels |
| command will use the appropriate format/type combination from |
| Table 8.15. For an internal format of RGBA8_SNORM, this will be |
| GL_RGBA and GL_BYTE. (Special rules apply to framebuffer |
| attachments that have been created using unsized internalformats. |
| These rules don't apply to attachments of _SNORM formats as they |
| could only have been created using sized internalformats.) The |
| following 'virtual' TexImage2D call will use the same format/type |
| combination together with the provided internalformat. The |
| resulting combination of internalformat/format/type must be one |
| of those listed in Table 8.12. For signed fixed point formats it |
| is not possible to create them from unsigned fixed point data and |
| vice versa. Effectively this means, CopyTexImage2D cannot perform |
| any conversions that glTexImage could not do (except dropping |
| color components); in particular it cannot convert between |
| mismatching component types. |
| |
| Source Effective | Requested | CopyTexImage Supported |
| Internalformat | Internalformat | |
| -----------------+------------------------+------------------------------------ |
| sized SNORM | sized SNORM | yes (provided component sizes match |
| | | and the same or more components |
| | | are present in the source buffer) |
| sized SNORM | sized or unsized UNORM | no (conversions not supported) |
| |
| |
| Revision History: |
| |
| Revision: 1 2014-07-18 (mheyer) |
| initial revision |
| Revision: 2 2014-08-08 (mheyer) |
| rename extension to EXT_render_snorm |
| Revision: 3 2014-08-20 (mheyer) |
| clarify CopyTexImage2D behavior |
| Revision: 4 2014-10-24 (dkoch) |
| mark complete, publishing cleanup |
