---
name: "icetDrawFunc"
section: "3"
platform: "linux"
package: "paraview"
version: "3.8.0-1+b1"
release: "Debian 6.0 (Squeeze)"
platforms: ["linux"]
url: "https://new.carta.tech/icetDrawFunc"
---

# icetDrawFunc(3)

## NAME

**icetDrawFunc -- set a callback for drawing.**

## Synopsis

\#include \<GL/ice-t.h\>

typedef void (\***IceTCallback**)(void);

| | | |
| --- | --- | --- |
| void **icetDrawFunc**( | **IceTCallback** | *func* ); |

## Description

The **icetDrawFunc** function sets a callback that is used to draw  the geometry from a given viewpoint.

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

*func* 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 *func* *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  *func* changes the background color, and severe color blending  artifacts may result.

**IceT** may call *func* several times from within a call to  **icetDrawFrame** 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 *func*. For example, counting frames by incrementing a  frame counter in *func* is obviously wrong (although you could count  how many times a render occurs). *func* should also leave **OpenGL**  in a state such that it will be correct for a subsequent run of  *func*. Any matrices or attributes pushed in *func* should be  popped before *func* returns, and any state that is assumed to be  true on entrance to *func* should also be true on return.

## Errors

None.

## Warnings

None.

## Bugs

None known.

## Notes

*func* is tightly coupled with the bounds set with  **icetBoundingVertices** or **icetBoundingBox**. If the geometry  drawn by *func* 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, there is a non-exclusive  license for use of this work by or on behalf of the U.S. Government.  Redistribution and use in source and binary forms, with or without  modification, are permitted provided that this Notice and any statement  of authorship are reproduced on all copies.

## See Also

[*icetDrawFrame*(3)](/icetDrawFrame/3.md), [*icetBoundingVertices*(3)](/icetBoundingVertices/3.md), [*icetBoundingBox*(3)](/icetBoundingBox/3.md)