_glLogicOp: specify a logical pixel operation for rendering
SUB _glLogicOp (BYVAL opcode AS _UNSIGNED LONG) void _glLogicOp(GLenum 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.
_glLogicOp specifies a logical operation that, when enabled, is applied between the incoming RGBA color and the 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. The initial value is disabled.
|_GL_AND||s & d|
|_GL_NAND||~(s & d)|
|_GL_XOR||s ^ d|
|_GL_EQUIV||~(s ^ d)|
|_GL_AND_REVERSE||s & ~d|
|_GL_AND_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 and d represents the color 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 colors.
When more than one RGBA color 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).
Logic operations have no effect on floating point draw buffers. However, if _GL_COLOR_LOGIC_OP is enabled, blending is still disabled in this case.
_GL_INVALID_ENUM is generated if opcode is not an accepted value.
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