Gl.SelectBuffer (gb.opengl)

Establish a buffer for selection mode values.

Parameters

size

Specifies the size of buffer.

buffer

Returns the selection data.

Description

Gl.SelectBuffer 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 Gl.InitNames, Gl.LoadName, Gl.PushName) when the rendering mode is Gl.SELECT (see Gl.RenderMode). Gl.SelectBuffer 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 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 Gl.RenderMode is called, a hit record is copied to buffer if any hits have occurred since the last such event (name stack change or Gl.RenderMode 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 /wiki/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(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 Gl.RenderMode with an argument other than Gl.SELECT. Whenever Gl.RenderMode 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 Gl.RenderMode was called, a negative hit record count is returned.

Notes

The contents of buffer is undefined until Gl.RenderMode is called with an argument other than Gl.SELECT.

Gl.Begin/Gl.End primitives and calls to Gl.RasterPos can result in hits. Gl.WindowPos will always generate a selection hit.

Errors

Gl.INVALID_VALUE is generated if size is negative.

Gl.INVALID_OPERATION is generated if Gl.SelectBuffer is called while the render mode is Gl.SELECT, or if Gl.RenderMode is called with argument Gl.SELECT before Gl.SelectBuffer is called at least once.

Gl.INVALID_OPERATION is generated if Gl.SelectBuffer is executed between the execution of Gl.Begin and the corresponding execution of Gl.End.

Associated Gets

Gl.Get with argument Gl.NAME_STACK_DEPTH

Gl.Get with argument Gl.SELECTION_BUFFER_SIZE

Gl.GetPointerv with argument Gl.SELECTION_BUFFER_POINTER

See also

See original documentation on OpenGL website