A
glAccum
Chapter 1
11
Each component value is divided by 2
n
-1, where n is the number of
bits allocated to each color component in the currently selected buffer.
The result is a floating-point value in the range [0, 1], which is
multiplied by value and added to the corresponding pixel component in
the accumulation buffer, thereby updating the accumulation buffer.
GL_LOAD Similar to GL_ACCUM, except that the current value in the
accumulation buffer is not used in the calculation of the new value.
That is, the R, G, B, and A values from the currently selected buffer are
divided by 2
n
- 1, multiplied by value, and then stored in the
corresponding accumulation buffer cell, overwriting the current value.
GL_ADD Adds value to each R, G, B, and A in the accumulation buffer.
GL_MULT Multiplies each R, G, B, and A in the accumulation buffer by value and
returns the scaled component to its corresponding accumulation buffer
location.
GL_RETURN Transfers accumulation buffer values to the color buffer or buffers
currently selected for writing. Each R, G, B, and A component is
multiplied by value, then multiplied by 2
n
- 1, clamped to the range [0,
2
n
- 1], and stored in the corresponding display buffer cell. The only
fragment operations that are applied to this transfer are pixel
ownership, scissor, dithering, and color writemasks.
To clear the accumulation buffer, call glClearAccum with R, G, B, and A values to set it
to, then call glClear with the accumulation buffer enabled.
Notes
Only pixels within the current scissor box are updated by a glAccum operation.
Errors
• GL_INVALID_ENUM is generated if op is not an accepted value.
• GL_INVALID_OPERATION is generated if there is no accumulation buffer.
• GL_INVALID_OPERATION is generated if glAccum is executed between the
execution of glBegin and the corresponding execution of glEnd.
Associated Gets
glGet with argument GL_ACCUM_RED_BITS
glGet with argument GL_ACCUM_GREEN_BITS
glGet with argument GL_ACCUM_BLUE_BITS
glGet with argument GL_ACCUM_ALPHA_BITS
See Also
glBlendFunc,
glClear,
glClearAccum,
glCopyPixels,
glGet,
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