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glLogicOp
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glLogicOp: specify a logical pixel operation for color index rendering.

C Specification | Parameters | Description | Notes | Errors | Associated Gets | See Also

[Up] C Specification

void glLogicOp(
    GLenum	 opcode)

[Up] Parameters

opcode
Specifies a symbolic constant that selects a logical operation. The following symbols are accepted: GL_CLEAR, GL_SET, GL_COPY, GL_COPY_INVERTED, GL_NOOP, GL_INVERT, GL_AND, GL_NAND, GL_OR, GL_NOR, GL_XOR, GL_EQUIV, GL_AND_REVERSE, GL_AND_INVERTED, GL_OR_REVERSE, and GL_OR_INVERTED. The initial value is GL_COPY.

[Up] Description

glLogicOp specifies a logical operation that, when enabled, is applied between the incoming color index or RGBA color and the color index or RGBA color at the corresponding location in the frame buffer. To enable or disable the logical operation, call glEnable and glDisable using the symbolic constant GL_COLOR_LOGIC_OP for RGBA mode or GL_INDEX_LOGIC_OP for color index mode. The initial value is disabled for both operations.

Opcode Resulting
Value
GL_CLEAR 0
GL_SET 1
GL_COPY s
GL_COPY_INVERTED !s
GL_NOOP !d
GL_INVERT d
GL_AND s & d
GL_NAND ! (s & d)
GL_OR s | d
GL_NOR ! (s | d)
GL_XOR s ^ d
GL_EQUIV ! (s ^ d)
GL_AND_REVERSE s & !d
GL_AND_INVERTED !s & d
GL_OR_REVERSE s | !d
GL_OR_INVERTED !s | d

opcode is a symbolic constant chosen from the list above. In the explanation of the logical operations, s represents the incoming color index and d represents the index in the frame buffer. Standard C-language operators are used. As these bitwise operators suggest, the logical operation is applied independently to each bit pair of the source and destination indices or colors.

[Up] Notes

Color index logical operations are always supported. RGBA logical operations are supported only if the GL version is 1.1 or greater.

When more than one RGBA color or index buffer is enabled for drawing, logical operations are performed separately for each enabled buffer, using for the destination value the contents of that buffer (see glDrawBuffer).

[Up] Errors

[Up] Associated Gets

glGet with argument GL_LOGIC_OP_MODE.
glIsEnabled with argument GL_COLOR_LOGIC_OP or GL_INDEX_LOGIC_OP.

[Up] See Also

glAlphaFunc,
glBlendFunc,
glDrawBuffer,
glEnable,
glStencilOp

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