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GL3.2 for AIX: Graphics Library (GL) Technical Reference

czclear Subroutine


Clears the color bitplanes and the z-buffer simultaneously.


Graphics Library

C (libgl.a)

FORTRAN (libfgl.a)

C Syntax

void czclear(Int32 cval, Int32 zval)


INTEGER*4 cval, zval


The czclear subroutine simultaneously clears the color bitplanes to the value of the cval parameter and the z-buffer to the value of the zval parameter. The czclear subroutine clears all active color bits (8 or 12 in color map mode, 24 in RGB mode), and all 24 z-buffer bits. Pattern 0 (zero) is always used, regardless of the current pattern specification. The system ignores the current writemask.

Only the screen area inside the current screenmask is cleared. The screenmask cannot be made larger than the window. By default, the screenmask is exactly the same size as the window. Use the scrmsk subroutine to change the size of the screenmask.

Note: The viewport subroutine resets the screenmask to be precisely the same size as the viewport.

In RGB mode, the cval parameter requires a packed integer of the same format used by the cpack subroutine, 0xaaggbbrr, where rr is the red value, gg is the green value, bb is the blue value, and aa is the alpha value. In color map mode, the cval parameter requires an index into the current color map, so that only the bottom 8 or 12 bits are significant.

Whenever you need to clear both the z-buffer and the color bitplanes to constant values at the same time, use the czclear subroutine. The czclear subroutine executes as fast as, or faster than, the clear and zclear subroutines called sequentially.

The czclear subroutine can be called whether z-buffer mode is on or off. The current color does not change.

Note: The operation of this subroutine for the Supergraphics Processor Subsystem is modified. (See "Hardware Considerations" in GL3.2 Version 4 for AIX: Programming Concepts.)


cval Specifies the color to which to clear the color bitplanes.
zval Specifies the depth to which to clear the z-buffer. The zval parameter has the following values:
Values for the zval parameter
Min Max
-0x800000 0x7FFFFF

Implementation Specifics

This subroutine is part of GL in the AIXwindows Environment/6000 Version 1, Release 2 with AIXwindows/3D Feature.


/usr/include/gl/gl.h Contains C language constant and variable type definitions for GL.
/usr/include/gl/fgl.h Contains FORTRAN constant and variable type definitions for GL.

Related Information

Clearing to the screenmask with the clear subroutine.

Setting the current color as a packed 32-bit integer using the cpack subroutine.

Enabling and disabling the z-buffer for storing depth information with the zbuffer subroutine.

Clearing the z-buffer with the zclear subroutine.

Specifying the function used for depth comparison with the zfunction subroutine.

Understanding the Hardware Used by GL, Configuring the Frame Buffer, and Working in Color Map and RGB Modes.

Clearing, Resetting, and Initiliazing GL, Writemasks and Logical Operations.

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