glRenderMode(3G) OpenGL Reference glRenderMode(3G)NAME
glRenderMode - set rasterization mode
C SPECIFICATION
GLint glRenderMode( GLenum mode )
PARAMETERS
mode Specifies the rasterization mode. Three values are accepted:
GL_RENDER, GL_SELECT, and GL_FEEDBACK. The initial value is
GL_RENDER.
DESCRIPTION
glRenderMode sets the rasterization mode. It takes one argument, mode,
which can assume one of three predefined values:
GL_RENDER Render mode. Primitives are rasterized, producing pixel
fragments, which are written into the frame buffer. This
is the normal mode and also the default mode.
GL_SELECT Selection mode. No pixel fragments are produced, and no
change to the frame buffer contents is made. Instead, a
record of the names of primitives that would have been
drawn if the render mode had been GL_RENDER is returned
in a select buffer, which must be created (see
glSelectBuffer) before selection mode is entered.
GL_FEEDBACK Feedback mode. No pixel fragments are produced, and no
change to the frame buffer contents is made. Instead,
the coordinates and attributes of vertices that would
have been drawn if the render mode had been GL_RENDER is
returned in a feedback buffer, which must be created (see
glFeedbackBuffer) before feedback mode is entered.
The return value of glRenderMode is determined by the render mode at the
time glRenderMode is called, rather than by mode. The values returned
for the three render modes are as follows:
GL_RENDER 0.
GL_SELECT The number of hit records transferred to the select
buffer.
GL_FEEDBACK The number of values (not vertices) transferred to the
feedback buffer.
See the glSelectBuffer and glFeedbackBuffer reference pages for more
details concerning selection and feedback operation.
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glRenderMode(3G) OpenGL Reference glRenderMode(3G)NOTES
If an error is generated, glRenderMode returns 0 regardless of the
current render mode.
One particularly surprising error condition occurs when the selection or
feedback buffer is too large for the implementation to handle. The
problem might not be detected until glRenderMode is executed, because
buffer memory might not be allocated or locked down until that time. In
such a case, it is possible that the only indication of the error is that
glRenderMode will return zero. Thus it is especially important to check
the return value.
ERRORS
GL_INVALID_ENUM is generated if mode is not one of the three accepted
values.
GL_INVALID_OPERATION is generated if glSelectBuffer is called while the
render mode is GL_SELECT, or if glRenderMode is called with argument
GL_SELECT before glSelectBuffer is called at least once.
GL_INVALID_OPERATION is generated if glFeedbackBuffer is called while the
render mode is GL_FEEDBACK, or if glRenderMode is called with argument
GL_FEEDBACK before glFeedbackBuffer is called at least once.
GL_INVALID_OPERATION is generated if glRenderMode is executed between the
execution of glBegin and the corresponding execution of glEnd.
ASSOCIATED GETS
glGet with argument GL_RENDER_MODE
SEE ALSO
glFeedbackBuffer, glInitNames, glLoadName, glPassThrough, glPushName,
glSelectBuffer
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