HP Workstation zx2000 OpenGL 1.1 Reference for HP-UX 11.x - Page 10

A glAccum 10 glAccum glAccum: operate on the accumulation buffer. C Specification void glAccum( GLenum op, GLfloat value) Parameters op 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. 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 anti-aliasing (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). Chapter 1