---
name: "icetGLDrawCallback"
section: "3"
platform: "linux"
package: "paraview"
version: "5.13.2+dfsg-3"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/icetGLDrawCallback"
---

# icetGLDrawCallback(3)

## NAME

**icetGLDrawCallback -- set a callback for drawing with OpenGL .**

## Synopsis

**#include \<IceTGL.h\>**

**typedef void (\*** **IceTGLDrawCallbackType)( void );**

| | | |
| --- | --- | --- |
| void **icetGLDrawCallback**( | **IceTGLDrawCallbackType** | *callback* ); |

## Description

**The icetGLDrawCallback** **function sets a callback that is used to** **draw the geometry from a given viewpoint. It will be implicitly called** **from within icetGLDrawFrame.**

*callback* **should be a function that issues appropriate OpenGL**  **calls to draw geometry in the current OpenGL context. After** *callback* **is called, the image left in the frame buffer specified** **by icetGLSetReadBuffer** **will be read back for compositing.**

*callback* **should** *not* **modify the** **GL\_PROJECTION\_MATRIX** **as this would cause IceT to place image** **data in the wrong location in the tiled display and improperly cull** **geometry. It is acceptable to add transformations to** **GL\_MODELVIEW\_MATRIX,** **but the bounding vertices given with** **icetBoundingVertices** **or icetBoundingBox** **are assumed to** **already be transformed by any such changes to the modelview matrix.** **Also, GL\_MODELVIEW\_MATRIX** **must be restored before the draw** **function returns. Therefore, any changes to** **GL\_MODELVIEW\_MATRIX** **are to be done with care and should be** **surrounded by a pair of glPushMatrix and glPopMatrix functions.**

**It is also important that** *callback* *not* **attempt the change the** **clear color. In some composting modes, IceT needs to read, modify, and** **change the background color. These operations will be lost if** *callback* **changes the background color, and severe color blending** **artifacts may result.**

**IceT may call** *callback* **several times from within a call to** **icetGLDrawFrame** **or not at all if the current bounds lie outside** **the current viewpoint. This can have a subtle but important impact on** **the behavior of** *callback***.** **For example, counting frames by** **incrementing a frame counter in** *callback* **is obviously wrong** **(although you could count how many times a render occurs).** *callback* **should also leave OpenGL in a state such that it will be** **correct for a subsequent run of** *callback***.** **Any matrices or** **attributes pushed in** *callback* **should be popped before** *callback* **returns, and any state that is assumed to be true on** **entrance to** *callback* **should also be true on return.**

**The** *callback* **function pointer is placed in the** **ICET\_GL\_DRAW\_FUNCTION** **state variable.**

**icetGLDrawCallback** **is similar to icetDrawCallback.** **The** **difference is that the callback set by icetGLDrawCallback** **is used** **by icetGLDrawFrame** **and the callback set by** **icetDrawCallback** **is used by icetDrawFrame.**

## Errors

- **ICET\_INVALID\_OPERATION**

   **Raised if the icetGLInitialize** **has not been called.**

## Warnings

**None.**

## Bugs

**None known.**

## Notes

*callback* **is tightly coupled with the bounds set with** **icetBoundingVertices** **or icetBoundingBox.** **If the geometry** **drawn by** *callback* **is dynamic (changes from frame to frame), then the** **bounds may need to be changed as well. Incorrect bounds may cause the** **geometry to be culled in surprising ways.**

## Copyright

**Copyright (C)2003 Sandia Corporation**

**Under the terms of Contract DE-AC04-94AL85000 with Sandia Corporation, the** **U.S. Government retains certain rights in this software.**

**This source code is released under the New BSD License.**

## See Also

*icetBoundingBox***(3),** *icetBoundingVertices***(3),** *icetDrawCallback***(3),** *icetGLDrawFrame***(3)**