HP Workstation zx2000 OpenGL 1.1 Reference for HP-UX 11.x - Page 11

Chapter 1 A glAccum Each component value is divided by 2n -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 2n - 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 2n - 1, clamped to the range [0, 2n - 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, 11