This module corresponds to section 4.2 (Whole Framebuffer Operations) of the OpenGL 2.1 specs.
- auxBuffers :: GettableStateVar GLsizei
- doubleBuffer :: GettableStateVar Bool
- stereoBuffer :: GettableStateVar Bool
- rgbaBits :: GettableStateVar (Color4 GLsizei)
- stencilBits :: GettableStateVar GLsizei
- depthBits :: GettableStateVar GLsizei
- accumBits :: GettableStateVar (Color4 GLsizei)
- data BufferMode
- drawBuffer :: StateVar BufferMode
- drawBuffers :: StateVar [BufferMode]
- maxDrawBuffers :: GettableStateVar GLsizei
- indexMask :: StateVar GLuint
- colorMask :: StateVar (Color4 Capability)
- stencilMask :: StateVar GLuint
- stencilMaskSeparate :: Face -> SettableStateVar GLuint
- depthMask :: StateVar Capability
- data ClearBuffer
- clear :: [ClearBuffer] -> IO ()
- clearColor :: StateVar (Color4 GLclampf)
- clearIndex :: StateVar (Index1 GLfloat)
- clearStencil :: StateVar GLint
- clearDepth :: StateVar GLclampd
- clearAccum :: StateVar (Color4 GLfloat)
- data AccumOp
- accum :: AccumOp -> GLfloat -> IO ()
Querying the Buffer Configuration
The implementation and context dependent number of auxiliary buffers.
Selecting a Buffer for Writing
The set of color buffers which are selected for reading and writing.
No color buffers are selected.
Only the front left color buffer is selected.
Only the front right color buffer is selected.
Only the back left color buffer is selected.
Only the back right color buffer is selected.
Only the front left and front right color buffers are selected. If there is no front right color buffer, only the front left color buffer is selected.
Only the back left and back right color buffers are selected. If there is no back right color buffer, only the back left color buffer is selected.
Only the front left and back left color buffers are selected. If there is no back left color buffer, only the front left color buffer is selected.
Only the front right and back right color buffers are selected. If there is no back right color buffer, only the front right color buffer is selected.
All the front and back color buffers (front left, front right, back left, back right) are selected. If there are no back color buffers, only the front left and front right color buffers are selected. If there are no right color buffers, only the front left and back left color buffers are selected. If there are no right or back color buffers, only the front left color buffer is selected.
Only the given auxiliary color buffer no. i is selected.
When colors are written to the framebuffer, they are written into the color
buffers specified by
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.
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, a buffer may not appear more then once in the given
list. Specifying a buffer more then once will result in an
If fixed-function fragment shading is being performed,
specifies a set of draw buffers into which the fragment color is written.
If a fragment shader writes to
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
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
values of the fragment colors following shader execution are undefined, and
may differ for each fragment color.
Contains the maximum number of buffers that can activated via
or which can be simultaneously written into from within a fragment shader
using the special output variable array
gl_FragData. This constant
effectively defines the size of the
gl_FragData array. The minimum legal
value is 1.
Fine Control of Buffer Updates
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.
Controls the writing of individual bits in the stencil planes. The least significant n bits of its value, where n is the number of bits in the stencil buffer, specify a mask. Where a 1 appears in the mask, it is possible to write to the corresponding bit in the stencil buffer. Where a 0 appears, the corresponding bit is write-protected. Initially, all bits are enabled for writing.
Controls whether the depth buffer is enabled for writing. The initial state
Clearing the Buffers
The buffers which can be cleared with
The buffers currently enabled for color writing.
The accumulation buffer.
The stencil buffer.
The depth buffer.
Set the bitplane area of the window to values previously selected by
Multiple color buffers can be cleared simultaneously by selecting more than
one buffer at a time using
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
The value to which each buffer is cleared depends on the setting of the clear value for that buffer.
Controls the index c used by
clear to clear the color index buffers.
c is not clamped. Rather, c is converted to a fixed-point value with
unspecified precision to the right of the binary point. The integer part of
this value is then masked with 2^m-1, where m is the number of bits in a
color index stored in the framebuffer. Initially, the value is 0.
Controls the value s used by
clear to clear the stencil buffer. s is
masked with 2^m-1, where m is the number of bits in the stencil buffer.
Initially, the value is 0.
The Accumulation Buffer
An operation on the accumulation buffer.
Obtains R, G, B, and A values from the buffer currently
selected for reading (see
Transfers accumulation buffer values to the color buffer or buffers
currently selected for writing. Each R, G, B, and A component
is multiplied by the value given to
Multiplies each R, G, B, and A in the accumulation buffer by
the value given to
Adds the value given to
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.
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