When colors are written to the framebuffer, they are written into the color buffers specified by drawBuffer.

If more than one color buffer is selected for drawing, then blending or logical operations are computed and applied independently for each color buffer and can produce different results in each buffer.

Monoscopic contexts include only left buffers, and stereoscopic contexts include both left and right buffers. Likewise, single-buffered contexts include only front buffers, and double-buffered contexts include both front and back buffers. The context is selected at GL initialization.

The initial value is FrontBuffers for single-buffered contexts, and BackBuffers for double-buffered contexts.

drawBuffers defines the draw buffers to which all fragment colors are written. The draw buffers being defined correspond in order to the respective fragment colors. The draw buffer for fragment colors beyond those specified is set to NoBuffers.

Except for NoBuffers, a buffer may not appear more then once in the given list. Specifying a buffer more then once will result in an InvalidOperation.

If fixed-function fragment shading is being performed, drawBuffers specifies a set of draw buffers into which the fragment color is written.

If a fragment shader writes to gl_FragColor, drawBuffers specifies a set of draw buffers into which the single fragment color defined by gl_FragColor is written. If a fragment shader writes to gl_FragData, drawBuffers specifies a set of draw buffers into which each of the multiple fragment colors defined by gl_FragData are separately written. If a fragment shader writes to neither gl_FragColor nor gl_FragData, the values of the fragment colors following shader execution are undefined, and may differ for each fragment color.

Controls the writing of individual bits in the color index buffers. The least significant n bits of its value, where n is the number of bits in a color index buffer, specify a mask. Where a 1 appears in the mask, it is possible to write to the corresponding bit in the color index buffer (or buffers). Where a 0 appears, the corresponding bit is write-protected.

This mask is used only in color index mode, and it affects only the buffers currently selected for writing (see drawBuffer). Initially, all bits are enabled for writing.

Controls whether the individual color components in the framebuffer can or cannot be written. If the red flag is Disabled, for example, no change is made to the red component of any pixel in any of the color buffers, regardless of the drawing operation attempted. Initially, all color components can be written.

Changes to individual bits of components cannot be controlled. Rather, changes are either enabled or disabled for entire color components. Furthermore, this mask is used only in RGBA mode.

Set the bitplane area of the window to values previously selected by clearColor, clearIndex, clearDepth, clearStencil, and clearAccum. Multiple color buffers can be cleared simultaneously by selecting more than one buffer at a time using drawBuffer.

The pixel ownership test, the scissor test, dithering, and the buffer writemasks affect the operation of clear. The scissor box bounds the cleared region. Alpha function, blend function, logical operation, stenciling, texure mapping, and depth-buffering are ignored by clear.

clear takes a list of buffers, indicating which buffers are to be cleared. If a buffer is not present, then a clear directed at that buffer has no effect.

The value to which each buffer is cleared depends on the setting of the clear value for that buffer.

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 (see accumBits). 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.

accum operates on the accumulation buffer. The first argument selects an accumulation buffer operation. The second argument, is a floating-point value to be used in that operation, see AccumOp.

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 an accum operation results in a value outside the range [-1, 1], the contents of an accumulation buffer pixel component are undefined.

To clear the accumulation buffer, use clearAccum to specify the clear value, then call clear with the accumulation buffer enabled.