glAccum

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_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 oneof 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 byaccumulating 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 glGetIntergerv four times, with arguments GL_ACCUM_RED_BITS, GL_ACCUM_GREEN_BITS, GL_ACCUM_BLUE_BITS and GL_ACCUM_ALPHA_BITS, respectively. Regardless of the number of bits per component, however, 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 are applied identically to the red, green, blue and alpha components of each pixel. The contents of an accumulation buffer pixel component are undefined if the glAccum operation results in a value outside [-1, 1].

The operations are as follows:

GL_ACCUM

Obtains R, G, B and A values from the buffer currently selected for reading (see glClearAccum directive, and issuing a glClear command with the accumulation buffer enabled.

NOTES

Only those pixels within the current scissor box are updated by any 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 called between a call to glBegin and the corresponding call to 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