OpenGL-2.8.0.0: A binding for the OpenGL graphics system

Portabilityportable
Stabilitystable
Maintainersven.panne@aedion.de
Safe HaskellNone

Graphics.Rendering.OpenGL.GL.Framebuffer

Contents

Description

This module corresponds to section 4.2 (Whole Framebuffer Operations) of the OpenGL 2.1 specs.

Synopsis

Querying the Buffer Configuration

auxBuffers :: GettableStateVar GLsizeiSource

The implementation and context dependent number of auxiliary buffers.

doubleBuffer :: GettableStateVar BoolSource

True if front and back buffers exist.

stereoBuffer :: GettableStateVar BoolSource

True if left and right buffers exist.

Selecting a Buffer for Writing

data BufferMode Source

The set of color buffers which are selected for reading and writing.

Constructors

NoBuffers

No color buffers are selected.

FrontLeftBuffer

Only the front left color buffer is selected.

FrontRightBuffer

Only the front right color buffer is selected.

BackLeftBuffer

Only the back left color buffer is selected.

BackRightBuffer

Only the back right color buffer is selected.

FrontBuffers

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.

BackBuffers

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.

LeftBuffers

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.

RightBuffers

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.

FrontAndBackBuffers

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.

AuxBuffer GLsizei

Only the given auxiliary color buffer no. i is selected.

FBOColorAttachment GLsizei

Only the given color attachment of the bound framebufferobject is selected for reading or writing.

drawBuffer :: StateVar BufferModeSource

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 :: StateVar [BufferMode]Source

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.

drawBufferi :: DrawBufferIndex -> GettableStateVar BufferModeSource

drawBufferi is a fast query function. For indices in the range 0..maxDrawBuffers it's results are the same as selection the index from the list returned by drawBuffers. Though this function only uses one gl-function call instead of maxDrawBuffers + 1.

maxDrawBuffers :: GettableStateVar GLsizeiSource

Contains the maximum number of buffers that can activated via drawBuffers 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

indexMask :: StateVar GLuintSource

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.

colorMask :: StateVar (Color4 Capability)Source

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.

colorMaski :: DrawBufferIndex -> StateVar (Color4 Capability)Source

colorMaski is a version of colorMask that only applies to the specified drawbuffer

stencilMask :: StateVar GLuintSource

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.

depthMask :: StateVar CapabilitySource

Controls whether the depth buffer is enabled for writing. The initial state is Enabled.

Clearing the Buffers

data ClearBuffer Source

The buffers which can be cleared with clear.

Constructors

ColorBuffer

The buffers currently enabled for color writing.

AccumBuffer

The accumulation buffer.

StencilBuffer

The stencil buffer.

DepthBuffer

The depth buffer.

Instances

clear :: [ClearBuffer] -> IO ()Source

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.

clearColor :: StateVar (Color4 GLclampf)Source

Controls the red, green, blue, and alpha values used by clear to clear the color buffers. Values written into clearColor are clamped to the range [0, 1]. Initially, all values are 0.

clearIndex :: StateVar (Index1 GLfloat)Source

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.

clearStencil :: StateVar GLintSource

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.

clearDepth :: StateVar GLclampdSource

Controls the depth value used by clear to clear the depth buffer. Values written into clearDepth are clamped to the range [0, 1]. The initial value is 1.

clearAccum :: StateVar (Color4 GLfloat)Source

Controls the red, green, blue, and alpha values used by clear to clear the accumulation buffer. Values written into clearAccum are clamped to the range [-1, 1]. The initial values are all 0.

The Accumulation Buffer

data AccumOp Source

An operation on the accumulation buffer.

Constructors

Accum

Obtains R, G, B, and A values from the buffer currently selected for reading (see readBuffer). 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 the value given to accum and added to the corresponding pixel component in the accumulation buffer, thereby updating the accumulation buffer.

Load

Similar to 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 the value given to accum, and then stored in the corresponding accumulation buffer cell, overwriting the current value.

Return

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 accum, 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.

Mult

Multiplies each R, G, B, and A in the accumulation buffer by the value given to accum and returns the scaled component to its corresponding accumulation buffer location.

Add

Adds the value given to accum to each R, G, B, and A in the accumulation buffer.

Instances

Eq AccumOp 
Ord AccumOp 
Show AccumOp 

accum :: AccumOp -> GLfloat -> IO ()Source

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.