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glselectbuffer(3g) [xfree86 man page]

GLSELECTBUFFER(3G)														GLSELECTBUFFER(3G)

NAME
glSelectBuffer - establish a buffer for selection mode values C SPECIFICATION
void glSelectBuffer( GLsizei size, GLuint *buffer ) PARAMETERS
size Specifies the size of buffer. buffer Returns the selection data. DESCRIPTION
glSelectBuffer has two arguments: buffer is a pointer to an array of unsigned integers, and size indicates the size of the array. buffer returns values from the name stack (see glInitNames, glLoadName, glPushName) when the rendering mode is GL_SELECT (see glRenderMode). glSelectBuffer must be issued before selection mode is enabled, and it must not be issued while the rendering mode is GL_SELECT. A programmer can use selection to determine which primitives are drawn into some region of a window. The region is defined by the current modelview and perspective matrices. In selection mode, no pixel fragments are produced from rasterization. Instead, if a primitive or a raster position intersects the clip- ping volume defined by the viewing frustum and the user-defined clipping planes, this primitive causes a selection hit. (With polygons, no hit occurs if the polygon is culled.) When a change is made to the name stack, or when glRenderMode is called, a hit record is copied to buffer if any hits have occurred since the last such event (name stack change or glRenderMode call). The hit record consists of the number of names in the name stack at the time of the event, followed by the minimum and maximum depth values of all vertices that hit since the previous event, followed by the name stack contents, bottom name first. Depth values (which are in the range [0,1]) are multiplied by 2^32 - 1, before being placed in the hit record. An internal index into buffer is reset to 0 whenever selection mode is entered. Each time a hit record is copied into buffer, the index is incremented to point to the cell just past the end of the block of names - that is, to the next available cell. If the hit record is larger than the number of remaining locations in buffer, as much data as can fit is copied, and the overflow flag is set. If the name stack is empty when a hit record is copied, that record consists of 0 followed by the minimum and maximum depth values. To exit selection mode, call glRenderMode with an argument other than GL_SELECT. Whenever glRenderMode is called while the render mode is GL_SELECT, it returns the number of hit records copied to buffer, resets the overflow flag and the selection buffer pointer, and initial- izes the name stack to be empty. If the overflow bit was set when glRenderMode was called, a negative hit record count is returned. NOTES
The contents of buffer is undefined until glRenderMode is called with an argument other than GL_SELECT. glBegin/glEnd primitives and calls to glRasterPos can result in hits. ERRORS
GL_INVALID_VALUE is generated if size is negative. GL_INVALID_OPERATION is generated if glSelectBuffer is called while the render mode is GL_SELECT, or if glRenderMode is called with argu- ment GL_SELECT before glSelectBuffer is called at least once. GL_INVALID_OPERATION is generated if glSelectBuffer is executed between the execution of glBegin and the corresponding execution of glEnd. ASSOCIATED GETS
glGet with argument GL_NAME_STACK_DEPTH glGet with argument GL_SELECTION_BUFFER_SIZE glGetPointerv with argument GL_SELECTION_BUFFER_POINTER SEE ALSO
glFeedbackBuffer(3G), glInitNames(3G), glLoadName(3G), glPushName(3G), glRenderMode(3G) GLSELECTBUFFER(3G)

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GLRENDERMODE(3G)														  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 coordi- nates 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. NOTES
If an error is generated, glRenderMode returns 0 regardless of the current render mode. 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 argu- ment 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(3G), glInitNames(3G), glLoadName(3G), glPassThrough(3G), glPushName(3G), glSelectBuffer(3G) GLRENDERMODE(3G)
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