| Name |
| |
| SGIX_vertex_preclip |
| |
| Name Strings |
| |
| GL_SGIX_vertex_preclip |
| GL_SGIX_vertex_preclip_hint |
| |
| Contact |
| |
| John Francis, Silicon Graphics (jfrancis 'at' sgi.com) |
| Dave Gorgen, Silicon Graphics (dgorgen 'at' sgi.com) |
| |
| Status |
| |
| XXX - Not complete yet!!! |
| |
| Version |
| |
| Last Modified Date: April 19, 2000 |
| |
| Number |
| |
| 210 |
| |
| Dependencies |
| |
| OpenGL 1.2 is required. |
| |
| Overview |
| |
| Certain graphics subsystems are capable of performing fast |
| 2D viewport or, in some cases, 3D volume "scissoring" operations |
| within some coordinate range much faster that the host CPU could |
| re-tesselate clipped primitives. |
| |
| This extension introduces the notion of an extended rasterizable view |
| volume that is an expansion of the clip-space view volume. This volume |
| is the space within which a particular graphics system is much more |
| efficient at rejecting fragments that lie outside the view volume than |
| it is at performing strict view volume clipping. |
| |
| Clip-checking can be turned on or off through the glEnable/glDisable |
| mechanism, and can be further controlled by using glHint. |
| |
| IP Status |
| |
| None |
| |
| Issues |
| |
| Should more precise control be given, instead of just a hint? |
| |
| NO. (Or not yet, anyway). |
| |
| New Procedures and Functions |
| |
| None |
| |
| New Tokens |
| |
| Accepted by the <cap> parameter of Enable, Disable, and IsEnabled, |
| and the <pname> parameter of GetBooleanv, GetIntegerv, GetFloatv, |
| and GetDoublev: |
| |
| VERTEX_PRECLIP_SGIX 0x83EE |
| |
| Accepted by the <target> parameter of Hint and the <pname> parameter |
| of GetBooleanv, GetIntegerv, GetFloatv, and GetDoublev: |
| |
| VERTEX_PRECLIP_HINT_SGIX 0x83EF |
| |
| |
| Additions to Chapter 2 of the OpenGL 1.2.1 Specification (OpenGL Operation) |
| |
| At the end of section 2.11 Clipping Add: |
| |
| The precision of the arithmetic used in the clipping operation is |
| undefined. Some implementations may be able to maintain full |
| accuracy for all primitives, while other implementations may have |
| limits on the extent of a primitive, or retain full accuracy only |
| within some rasterizable volume (larger than the clip volume). |
| |
| Such implementations can make use of the VERTEX_PRECLIP extension. |
| If this feature is enabled, all primitives will be pre-clipped to |
| the rasterizable volume before any other processing. |
| |
| Additions to Chapter 3 of the OpenGL 1.2.1 Specification (Rasterization) |
| |
| None |
| |
| Additions to Chapter 4 of the OpenGL 1.2.1 Specification (Per-Fragment |
| Operations and the Frame Buffer) |
| |
| None |
| |
| Additions to Chapter 5 of the OpenGL 1.2.1 Specification (Special Functions) |
| |
| In section 5.6 Hints: |
| |
| remove the word 'and' in front of FOG_HINT |
| |
| replace the period after the description of FOG_HINT with |
| |
| ; and VERTEX_PRECLIP_HINT, indicating the strictness of |
| checking for primitives which extend beyond the rasterizable |
| volume. |
| |
| Additions to Chapter 6 of the OpenGL 1.2.1 Specification (State and |
| State Requests) |
| |
| Only the changes to tables 6.7 and 6.23 detailed below |
| |
| Additions to Appendix A of the OpenGL 1.2.1 Specification (Invariance) |
| |
| None |
| |
| Additions to the AGL/GLX/WGL Specifications |
| |
| None |
| |
| Errors |
| |
| None |
| |
| New State |
| |
| (table 6.7, Transformation State) |
| Initial |
| Get Value Type Get Command Value Description Sec. Attribute |
| --------- ---- ----------- ------- ----------- ---- --------- |
| VERTEX_PRECLIP B IsEnabled False Pre-clip On/Off 2.11 transform/enable |
| |
| |
| (table 6.23, Hints) |
| Initial |
| Get Value Type Get Command Value Description Sec. Attribute |
| --------- ---- ----------- ------- ----------- ---- --------- |
| VERTEX_PRECLIP_HINT Z3 GetIntegerv DONT_CARE Pre-clip Hint 5.6 hint |
| |
| New Implementation Dependent State |
| |
| None |
| |
| Revision History |
| |