glRenderMode.3G man page
glRenderMode — set rasterization mode
GLint glRenderMode(GLenum mode);
Specifies the rasterization mode. Three values are accepted: GL_RENDER, GL_SELECT, and GL_FEEDBACK. The initial value is GL_RENDER.
glRenderMode sets the rasterization mode. It takes one argument, mode, which can assume one of three predefined values:
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.
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.
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:
The number of hit records transferred to the select buffer.
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.
If an error is generated, glRenderMode returns 0 regardless of the current render mode.
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().
glGet() with argument GL_RENDER_MODE
glFeedbackBuffer(), glInitNames(), glLoadName(), glPassThrough(), glPushName(), glSelectBuffer()
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