glSelectBuffer — establish a buffer for selection mode values
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
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 clipping 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 , 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\(emthat 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 initializes the name stack to be empty. If the overflow bit was set when glRenderMode was called, a negative hit record count is returned.
The contents of
buffer is undefined until glRenderMode is called with an argument other than
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 argument
glSelectBuffer is called at least once.
glGet with argument
glGet with argument
glGetPointerv with argument
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