void PEXAccumulateBuffer( Display *display, Drawable drawable, float source_weight, float dest_weight )
None.
Invoke PEXAccumulateBuffer to accumulate the contents of drawable (D) into the ancillary accumulation buffer (A) associated with drawable using the source_weight (ws) and dest_weight (wd) as follows:
If underflow or overflow occurs, then the result is implementation-dependent.
See Accumulation Buffers for an overview.