Porting Screen and Buffer Clearing Commands
OpenGL replaces a variety of IRIS GL clear functions (such as zclear, aclear, sclear, and so on) with a single function, glClear. Specify exactly what you want to clear by passing masks to glClear.
Keep the following points in mind when porting screen and buffer commands:
Instead of using one of several differently named clear calls, you now clear several buffers with one call, glClear, by OR ing together buffer masks. For example, czclear is replaced by:
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT )
IRIS GL references the polygon stipple and the color writemask. OpenGL ignores the polygon stipple but references the color writemask. (The czclear function ignores both the polygon stipple and the color writemask.)
The following table lists the various IRIS GL clear functions with their equivalent OpenGL functions.
|IRIS GL call||OpenGL call||Meaning|
|acbuf(AC_CLEAR)||glClear( GL_ACCUM_BUFFER_BIT )||Clear the accumulation buffer.|
|glClearColor||Set the RGBA clear color.|
|glClearIndex||Set the clear-color index.|
|clear||glClear( GL_COLOR_BUFFER_BIT )||Clear the color buffer.|
|glClearDepth||Specify the clear value for the depth buffer.|
|zclear||glClear( GL_DEPTH_BUFFER_BIT )||Clear the depth buffer.|
|czclear||glClear( GL_COLOR_BUFFER_BIT |GL_DEPTH_BUFFER_BIT )
||Clear the color buffer and the depth buffer.|
|glClearAccum||Specify clear values for the accumulation buffer.|
|glClearStencil||Specify the clear value for the stencil buffer.|
|sclear||glClear( GL_STENCIL_BUFFER_BIT )||Clear the stencil buffer.|
When your IRIS GL code uses both gclear and sclear, you can combine them into a single glClear call; can improve your program's performance.