Attachment 71244 Details for Bug 57875 – proposed MESA_clip_disable extension

proposed MESA_clip_disable extension

MESA_clip_disable.txt (text/plain), 4.02 KB, created by Stefan Dösinger on 2012-12-09 21:59:53 UTC

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Creator: Stefan Dösinger

Created: 2012-12-09 21:59:53 UTC

Size: 4.02 KB

patch

obsolete

>Name
>
>    MESA_clip_disable
>
>Name Strings
>
>    GL_MESA_clip_disable
>
>Contact
>
>    Stefan DÃ¶singer (stefan 'at' codeweavers.com)
>
>Status
>
>    Draft
>    TODO: Token values
>    TODO: Formal language defining interaction with gl_FragCoord
>    TODO: Implementation dependent state
>    TODO: Number
>
>Version
>
>    Version 1, 2012/12/9
>
>Number
>
>    ???
>
>Dependencies
>
>    Written based on the wording of the OpenGL 3.1 specification.
>
>    Some wording taken from ARB_depth_clamp.
>
>    ARB_depth_clamp must not be supported.
>
>Overview
>
>    This extension exposes the ability to disable the near and far clipping
>    planes in a way simmilar to ARB_depth_clamp without specifying clamping
>    behavior. It is intended to be used with orthogonal transformation matrices
>    and the depth test disabled. If ARB_depth_clamp is supported by the
>    driver, this extension must not be exposed.
>
>    This extension guarantees that geometry outside the near and far planes of
>    the clip volume are rendered if the depth test is disabled. If the depth
>    test is enabled the behavior is undefined. Reading gl_FragCoord inside a
>    fragment shader is undefined.
>
>    This functionality is provided for porting applications that use another
>    popular 3D API and draw pre-transformed and pre-clipped geometry with the
>    depth test disabled.
>
>Issues
>
>    Should we reuse the DEPTH_CLAMP token?
>
>        UNRESOLVED: Probably not. The behavior is different and the two should
>        not be confused.
>
>        Applications that detect the presence of ARB_depth_clamp by enabling
>        DEPTH_CLAMP and check for an error may be misguided.
>
>    What are the interactions with the raster position?
>
>        UNRESOLVED: Probably the same as in ARB_depth_clamp for the reasons
>        listed there.
>
>New Procedures and Functions
>
>    None
>
>New Tokens
>
>    Accepted by the <cap> parameter of Enable, Disable, and IsEnabled,
>    and by the <pname> parameter of GetBooleanv, GetIntegerv,
>    GetFloatv, and GetDoublev:
>
>    CLIP_ENABLE_MESA              0x????
>
>Additions to Chapter 2 of the OpenGL 3.1 Specification (OpenGL Operation)
>
> --  Section 2.17 "Clipping"
>
>    Add to the end of the 3rd paragraph:
>
>    "Clipping is enabled with the generic Enable command and
>    disabled with the Disable command. The value of the argument to
>    either command is CLIP_ENABLE_MESA. If depth clamping is enabled, the
>    "-w_c <= z_c <= w_c" plane equation are ignored by view volume
>    clipping (effectively, there is no near or far plane clipping)."
>
>    If and only if the ARB_compatibility extension is supported:
>
> --  Section 2.22 "Current Raster Position"
>
>    Add to the end of the 4th paragraph:
>
>    "If clipping (see section 2.17) is disabled, then raster
>    position z_w is first clamped to the range [min(n,f),max(n,f)],
>    where n and f are the current near and far depth range values (see
>    section 2.12.1)."
>
>Additions to Chapter 3 of the OpenGL 3.1 Specification (Rasterization)
>
>    None
>
>Additions to Chapter 4 of the OpenGL 3.1 Specification (Per-Fragment Operations
>and the Framebuffer)
>
> --  Section 4.1.5 "Depth buffer test"
>
>    Add to the end of the 2nd paragraph:
>
>    "If clipping (see section 2.17) is disabled, and the depth test
>    is enabled, the results are undefined."
>
>Additions to Chapter 5 of the OpenGL 3.1 Specification (Special Functions)
>
>    None
>
>Additions to Chapter 6 of the OpenGL 3.1 Specification (State and State Requests)
>
>    None
>
>Additions to the AGL/GLX/WGL Specifications
>
>    None
>
>GLX Protocol
>
>    None
>
>Errors
>
>    None
>
>New State
>
>Add to table 6.7, transformation state
>
>Get Value   Type  Get Command  Initial Value  Description     Sec      Attribute
>----------  ----  -----------  -------------  --------------  ------   ----------------
>CLIP_MESA   B     IsEnabled    True           Depth clipping  2.12.2   transform/enable
>                                              on/off
>
>New Implementation Dependent State
>
>    ???
>
>Interactions with ARB_compatibility
>
>    If ARB_compatibility is not supported, the language about current
>    raster position in section 2.22 is removed.

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Attachments on bug 57875: 70995 | 71244 | 71407

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