GLACCUM man page on RedHat
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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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