| Name |
| |
| IMG_user_clip_plane |
| |
| Name Strings |
| |
| GL_IMG_user_clip_plane |
| |
| Notice |
| |
| Copyright Imagination Technologies Limited, 2005. |
| |
| Contact |
| |
| Imagination Technologies |
| |
| Status |
| |
| FINAL |
| |
| Version |
| |
| 1.0, 11 May 2009 |
| |
| Number |
| |
| OpenGL ES Extension #57 |
| |
| Dependencies |
| |
| The extension is written against the OpenGLES 1.0 Specification. |
| |
| Overview |
| |
| The OpenGL ES 1.0 Specification does not support user clip planes. This extension |
| adds the support for clip planes. This extension was superceded by OpenGL ES 1.1 |
| |
| IP Status |
| |
| None |
| |
| Issues |
| |
| None |
| |
| New Procedures and Functions |
| |
| For the COMMON profile: |
| void ClipPlanefIMG( GLenum p, GLfloat eqn[4] ); |
| |
| For the COMMON_LITE profile: |
| void ClipPlanexIMG( GLenum p, GLfixed eqn[4] ); |
| |
| |
| |
| New Tokens |
| |
| Accepted by the <pname> parameter of GetIntegerv function: |
| |
| MAX_CLIP_PLANES_IMG 0x0D32 |
| |
| Accepted by the <pname> parameter of ClipPlanef, ClipPlanex, Enable and Disable: |
| |
| CLIP_PLANE0_IMG 0x3000 |
| CLIP_PLANE1_IMG 0x3001 |
| CLIP_PLANE2_IMG 0x3002 |
| CLIP_PLANE3_IMG 0x3003 |
| CLIP_PLANE4_IMG 0x3004 |
| CLIP_PLANE5_IMG 0x3005 |
| |
| |
| |
| Additions to OpenGLES 1.0 Specification |
| |
| Additions to Chapter 2.11 of the OpenGL ES 1.0 Specification (Clipping) |
| |
| (append after the last paragraph, after: "User-specified clipping [...]") |
| In the presence of IMG_user_clip_plane a number of 6 clip planes will be |
| exported to the user. The clip planes will restrict the view volume by defining |
| half spaces. The intersection between those half spaces and the view volume |
| defined by the back and front clipping plane represents the space where the |
| geometry will be clipped. To define a clip plane the application must provide |
| a plane equation by calling: |
| |
| ClipPlanefIMG(enum p, float eqn[4]) |
| ClipPlanexIMG(enum p, fixed eqn[4]) |
| |
| where p describes which clip plane is currently set, CLIP_PLANEi, and eqn are 4 |
| floating point values, in COMMON profile and 4 fixed values in COMMON_LITE |
| profile. The equation is represented by 4 values p1, p2, p3 and p4 which are |
| multiplied by the inverse of the modelview matrix transforming them into |
| eye space. |
| |
| ( p1' p2' p3' p4' ) = ( p1 p2 p3 p4 ) M^-1 |
| |
| Any vertex in eye space that satisfies the mathematical inequality will not be |
| clipped, becuase they are located in the positive half space of the clip plane: |
| |
| ( p1' p2' p3' p4' ) ( x y z w )^T >= 0 |
| |
| Clip planes need to be enabled in order to be used and this is done using |
| |
| Enable(enum p) |
| |
| where p is one of the clip planes enumerants, CLIP_PLANEi. If geometry is drawn |
| with a specific clip plane enabled without specifing the clip plane equation |
| the clipping results are undefined. |
| |
| To disable a clip plane, which is to disable clipping by that plane an application |
| must call |
| |
| Disable(enum p) |
| |
| where p is one of the clip planes enumerants, CLIP_PLANEi. |
| |
| Even though this extension specifies a number of 6 clip planes more can be exported |
| by different implementations. To find the maximum number of clip planes exported |
| an application must call |
| |
| GetIntegerv(enum p, int *params) |
| |
| Where p is MAX_CLIP_PLANES_IMG. After a call to this function <params> will contain |
| the number of clip planes exported by that particular extension. |
| |
| Errors |
| |
| INVALID_ENUM is generated by ClipPlanefIMG, ClipPlanexIMG, Enable and Disable if the |
| <pname> parameter is not one of the clip plane defines. |
| |
| New State |
| |
| Get Value Get Command Type Initial Value Attribute |
| --------- ----------- ---- ------------- --------- |
| MAX_CLIP_PLANES_IMG GetIntegerv N+ 6 user clip planes |
| |
| |
| Conformance Testing |
| |
| An easy way to test the conformance of user clip planes is to set up an ortographic |
| projection and use all clip planes, together and separate, oriented across the 3 axes |
| (negative and positive), and check for correct geometry clipping. |
| |
| Revision History |
| |
| 0.1, 17/2/2004 vs: Initial revision. |
| 0.2, 3/11/2004 bcb: Renamed entrypoints to add IMG suffix. |
| 0.3, 25/01/2005 nt: Added copyright notice and Number paragraph placeholder. |
| 1.0, 11/05/2009 bcb: Final cleanup for publication |
| |
| |
