man glLogicOp (3): specify a logical pixel operation for rendering

C SPECIFICATION

void glLogicOp(GLenum opcode);

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.

DESCRIPTION

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.

Opcode	Resulting Operation
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 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.

NOTES

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.

ERRORS

GL_INVALID_ENUM is generated if opcode is not an accepted value.

ASSOCIATED GETS

glGet() with argument GL_LOGIC_OP_MODE.

glIsEnabled() with argument GL_COLOR_LOGIC_OP.