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GLACCUM(3G)			 OpenGL Manual			   GLACCUM(3G)

NAME
       glAccum - operate on the accumulation buffer

C SPECIFICATION
       void glAccum(GLenum op, GLfloat value);

PARAMETERS
       op
	   Specifies the accumulation buffer operation. Symbolic constants
	   GL_ACCUM, GL_LOAD, GL_ADD, GL_MULT, and GL_RETURN are accepted.

       value
	   Specifies a floating-point value used in the accumulation buffer
	   operation.  op determines how value is used.

DESCRIPTION
       The accumulation buffer is an extended-range color buffer. Images are
       not rendered into it. Rather, images rendered into one of the color
       buffers are added to the contents of the accumulation buffer after
       rendering. Effects such as antialiasing (of points, lines, and
       polygons), motion blur, and depth of field can be created by
       accumulating images generated with different transformation matrices.

       Each pixel in the accumulation buffer consists of red, green, blue, and
       alpha values. The number of bits per component in the accumulation
       buffer depends on the implementation. You can examine this number by
       calling glGetIntegerv() four times, with arguments GL_ACCUM_RED_BITS,
       GL_ACCUM_GREEN_BITS, GL_ACCUM_BLUE_BITS, and GL_ACCUM_ALPHA_BITS.
       Regardless of the number of bits per component, the range of values
       stored by each component is -1 1. The accumulation buffer pixels are
       mapped one-to-one with frame buffer pixels.

       glAccum operates on the accumulation buffer. The first argument, op, is
       a symbolic constant that selects an accumulation buffer operation. The
       second argument, value, is a floating-point value to be used in that
       operation. Five operations are specified: GL_ACCUM, GL_LOAD, GL_ADD,
       GL_MULT, and GL_RETURN.

       All accumulation buffer operations are limited to the area of the
       current scissor box and applied identically to the red, green, blue,
       and alpha components of each pixel. If a glAccum operation results in a
       value outside the range -1 1, the contents of an accumulation buffer
       pixel component are undefined.

       The operations are as follows:

       GL_ACCUM
	   Obtains R, G, B, and A values from the buffer currently selected
	   for reading (see glReadBuffer()). 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
       glClear(), glClearAccum(), glCopyPixels(), glDrawBuffer(), glGet(),
       glReadBuffer(), glReadPixels(), glScissor(), glStencilOp()

COPYRIGHT
       Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed
       under the SGI Free Software B License. For details, see
       http://oss.sgi.com/projects/FreeB/.

AUTHORS
       opengl.org

opengl.org			  03/16/2013			   GLACCUM(3G)

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