extensions/IBM/IBM_rasterpos_clip.txt

Name

    IBM_rasterpos_clip

Name Strings

    GL_IBM_rasterpos_clip

Version

    $Id: //depot/main/doc/registry/extensions/IBM/rasterpos_clip.spec#1 $

Number

    110

Dependencies

    None

Overview

    IBM_rasterpos_clip extends the semantics of the RasterPos functions.  It
    provides an enable that allows a raster position that would normally be
    clipped to be treated as a valid (albeit out-of-viewport) position.

    This extension allows applications to specify geometry-aligned pixel
    primitives that may be partially off-screen.  These primitives are
    tested on a pixel-by-pixel basis without being rejected completely
    because of an invalid raster position.

Issues

    Currently, clipping is disabled only in X and Y.  If disabling Z
    clipping is required, the behavior needs to be specified.

New Procedures and Functions

    None

New Tokens
        
    Accepted by the <target> parameter of Enable and Disable and the <value>
    parameter of IsEnabled, GetBooleanv, GetIntegerv, GetFloatv, GetDoublev:

        RASTER_POSITION_UNCLIPPED_IBM           103010

    The enum is subject to change if this proposal attracts interest from
    other vendors and becomes an EXT extension.

Additions to Chapter 2 of the GL Specification (OpenGL Operation)

    In Section 2.12, the behavior of valid bit of the raster position with
    respect to vertex clipping is defined.

        The transformed coordinates are passed to clipping as if they
        represented a point.  If the "point" is not culled, then the
        projection to window coordinates is computed (section 2.10) and
        saved as the current raster position, and the valid bit is set.  If
        the "point" is culled, ... the valid bit is cleared.

    The specification is modified to read:

        The transformed coordinates are passed to clipping as if they
        represented a point.  If (1) the "point" is not culled, or (2)
        RASTER_POSITION_UNCLIPPED_IBM is enabled and the "point" is not culled
        except by the x and y components of the clip volume, then the
        projection to window coordinates is computed (section 2.10) and saved
        as the current raster position, and the valid bit is set.  Otherwise,
        ... the valid bit is cleared.


Additions to Chapter 3 of the GL Specification (Rasterization)

    None

Additions to Chapter 4 of the GL Specification (Per-Fragment Operations
and the Framebuffer)

    None

Additions to Chapter 5 of the GL Specification (Special Functions)

    None

Additions to Chapter 6 of the GL Specification (State and State Requests)

    None

Additions to the GLX Specification

    None

GLX Protocol

    None (other than the new Enable target).

Errors

    None

New State

    Get Value                     Type Get Command  Value Sec   Attrib
    ----------------------------- ---- -----------  ----- ----  -------
    RASTER_POSITION_UNCLIPPED_IBM   B  IsEnabled    False 2.12  transform/
                                                                enable 

New Implementation Dependent State

    None