glclear(3g) [osx man page]
GLCLEAR(3G) GLCLEAR(3G) NAME
glClear - clear buffers to preset values C SPECIFICATION
void glClear( GLbitfield mask ) PARAMETERS
mask Bitwise OR of masks that indicate the buffers to be cleared. The four masks are GL_COLOR_BUFFER_BIT, GL_DEPTH_BUFFER_BIT, GL_ACCUM_BUFFER_BIT, and GL_STENCIL_BUFFER_BIT. DESCRIPTION
glClear sets the bitplane area of the window to values previously selected by glClearColor, glClearIndex, glClearDepth, glClearStencil, and glClearAccum. Multiple color buffers can be cleared simultaneously by selecting more than one buffer at a time using glDrawBuffer. The pixel ownership test, the scissor test, dithering, and the buffer writemasks affect the operation of glClear. The scissor box bounds the cleared region. Alpha function, blend function, logical operation, stenciling, texture mapping, and depth-buffering are ignored by glClear. glClear takes a single argument that is the bitwise OR of several values indicating which buffer is to be cleared. The values are as follows: GL_COLOR_BUFFER_BIT Indicates the buffers currently enabled for color writing. GL_DEPTH_BUFFER_BIT Indicates the depth buffer. GL_ACCUM_BUFFER_BIT Indicates the accumulation buffer. GL_STENCIL_BUFFER_BIT Indicates the stencil buffer. The value to which each buffer is cleared depends on the setting of the clear value for that buffer. NOTES
If a buffer is not present, then a glClear directed at that buffer has no effect. ERRORS
GL_INVALID_VALUE is generated if any bit other than the four defined bits is set in mask. GL_INVALID_OPERATION is generated if glClear is executed between the execution of glBegin and the corresponding execution of glEnd. ASSOCIATED GETS
glGet with argument GL_ACCUM_CLEAR_VALUE glGet with argument GL_DEPTH_CLEAR_VALUE glGet with argument GL_INDEX_CLEAR_VALUE glGet with argument GL_COLOR_CLEAR_VALUE glGet with argument GL_STENCIL_CLEAR_VALUE SEE ALSO
glClearAccum, glClearColor, glClearDepth, glClearIndex, glClearStencil, glColorMask, glDepthMask, glDrawBuffer, glScissor, glStencilMask GLCLEAR(3G)
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GLACCUM(3G) GLACCUM(3G) 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_ACCUM, 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 one of the color buffers are added to the contents of the accumulation buffer after rendering. Effects such as antialiasing (of points, lines, and poly- gons), 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 buf- fer 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). 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 value and added to the corresponding pixel com- ponent in the accumulation buffer, thereby updating the accumulation buffer. GL_LOAD Similar to GL_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 value, and then stored in the corresponding accumulation buffer cell, overwriting the current value. GL_ADD Adds value to each R, G, B, and A in the accumulation buffer. GL_MULT Multiplies each R, G, B, and A in the accumulation buffer by value and returns the scaled component to its corresponding accumulation buffer location. GL_RETURN Transfers accumulation buffer values to the color buffer or buffers currently selected for writing. Each R, G, B, and A com- ponent is multiplied by value, 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. To clear the accumulation buffer, call glClearAccum with R, G, B, and A values to set it to, then call glClear with the accumulation buffer enabled. NOTES
Only pixels within the current scissor box are updated by a 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 executed between the execution of glBegin and the corresponding execution of 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 SEE ALSO
glClear, glClearAccum, glCopyPixels, glDrawBuffer, glGet, glReadBuffer, glReadPixels, glScissor, glStencilOp GLACCUM(3G)