man glReadBuffer (3): select a color buffer source for pixels

C SPECIFICATION

void glReadBuffer(GLenum mode);

PARAMETERS

mode

: Specifies a color buffer. Accepted values are GL_FRONT_LEFT, GL_FRONT_RIGHT, GL_BACK_LEFT, GL_BACK_RIGHT, GL_FRONT, GL_BACK, GL_LEFT, GL_RIGHT, and the constants GL_COLOR_ATTACHMENTi.

DESCRIPTION

glReadBuffer specifies a color buffer as the source for subsequent glReadPixels(), glCopyTexImage1D(), glCopyTexImage2D(), glCopyTexSubImage1D(), glCopyTexSubImage2D(), and glCopyTexSubImage3D() commands. mode accepts one of twelve or more predefined values. In a fully configured system, GL_FRONT, GL_LEFT, and GL_FRONT_LEFT all name the front left buffer, GL_FRONT_RIGHT and GL_RIGHT name the front right buffer, and GL_BACK_LEFT and GL_BACK name the back left buffer. Further more, the constants GL_COLOR_ATTACHMENTi may be used to indicate the ith color attachment where i ranges from zero to the value of GL_MAX_COLOR_ATTACHMENTS minus one.

Nonstereo double-buffered configurations have only a front left and a back left buffer. Single-buffered configurations have a front left and a front right buffer if stereo, and only a front left buffer if nonstereo. It is an error to specify a nonexistent buffer to glReadBuffer.

mode is initially GL_FRONT in single-buffered configurations and GL_BACK in double-buffered configurations.

ERRORS

GL_INVALID_ENUM is generated if mode is not one of the twelve (or more) accepted values.

GL_INVALID_OPERATION is generated if mode specifies a buffer that does not exist.

ASSOCIATED GETS

glGet() with argument GL_READ_BUFFER

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