glAccum - operate on the accumulation buffer
void glAccum(
GLenum op,
GLfloat value );
Specifies the accumulation buffer operation. Symbolic constants
GL_ACCUM, GL_LOAD, GL_ADD, GL_MULT, and GL_RETURN
are accepted. Specifies a floating-point value used in
the accumulation buffer operation. op determines how
value is used.
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-toone
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: 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. 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. Adds value to each R, G, B, and A in
the accumulation buffer. Multiplies each R, G, B, and A
in the accumulation buffer by value and returns the scaled
component to its corresponding accumulation buffer location.
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.
Only pixels within the current scissor box are updated by
a glAccum() operation.
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().
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
glClear(3), glClearAccum(3), glCopyPixels(3), glDrawBuffer(3), glGet(3), glReadBuffer(3), glReadPixels(3),
glScissor(3), glStencilOp(3)
glAccum(3G)
[ Back ] |
