HP Workstation zx2000 OpenGL 1.1 Reference for HP-UX 11.x - Page 150

F glFeedbackBuffer glFeedbackBuffer glFeedbackBuffer: controls feedback mode. C Specification void glFeedbackBuffer( GLsizei size, GLenum type, GLfloat *buffer) Parameters size Specifies the maximum number of values that can be written into buffer. type Specifies a symbolic constant that describes the information that will be returned for each vertex. GL_2D, GL_3D, GL_3D_COLOR, GL_3D_COLOR_TEXTURE, and GL_4D_COLOR_TEXTURE are accepted. size Returns the feedback data. Description The glFeedbackBuffer function controls feedback. Feedback, like selection, is a GL mode. The mode is selected by calling glRenderMode with GL_FEEDBACK. When the GL is in feedback mode, no pixels are produced by rasterization. Instead, information about primitives that would have been rasterized is fed back to the application using the GL. glFeedbackBuffer has three arguments: buffer is a pointer to an array of floating-point values into which feedback information is placed. size indicates the size of the array. type is a symbolic constant describing the information that is fed back for each vertex. glFeedbackBuffer must be issued before feedback mode is enabled (by calling glRenderMode with argument GL_FEEDBACK). Setting GL_FEEDBACK without establishing the feedback buffer, or calling glFeedbackBuffer while the GL is in feedback mode, is an error. When glRenderMode is called while in feedback mode, it returns the number of entries placed in the feedback array, and resets the feedback array pointer to the base of the feedback buffer. The returned value never exceeds size. If the feedback data required more room than was available in buffer, glRenderMode returns a negative value. To take the GL out of feedback mode, call glRenderMode with a parameter value other than GL_FEEDBACK. While in feedback mode, each primitive, bitmap, or pixel rectangle that would be rasterized generates a block of values that are copied into the feedback array. If doing so would cause the number of entries to exceed the maximum, the block is partially written so as to fill the array (if there is any room left at all), and an overflow flag is set. Each block begins with a code indicating the primitive type, followed by values that describe the primitive's vertices and associated data. Entries are also written for bitmaps and pixel rectangles. Feedback occurs after polygon culling and glPolygonMode interpretation of polygons has taken place, so polygons that are culled are not returned 150 Chapter 6