NAME glXGetTransparentIndexSUN - get the transparent pixel index for an overlay/underlay Window pair. C SPECIFICATION Status glXGetTransparentIndexSUN( Display *dpy, Window overlay, Window underlay, unsigned long *pTransparentIndex ) PARAMETERS dpy Specifies the connection to the X server overlay Specifies the overlay Window of an overlay/underlay pair. underlay Specifies the underlay Window. pTransparentIndex Specifies a pointer to the index to be returned. RETURN If underlay is a Window that has previously been made the current GLXDrawable by the client, and a transparent index is available for the overlay Window, glXGetTransparentIndexSUN returns 1 and sets *pTransparen- tIndex to the value of the index. Otherwise, it returns 0. If underlay is equal to None, and if a transparent index is available for overlay that is independent of the underlying Windows, glXGetTransparentIndexSUN returns 1 and sets *pTransparentIndex to the index. Otherwise, it returns 0. DESCRIPTION For some overlay Windows (windows created with a visual with GLX_LEVEL > 0), there is a particular color index that when drawn to the framebuffer causes pixels in the Window to be transparent. That is, pixels in the overlay drawn with the transparent index are invisible and the pixels of window(s) beneath the overlay are displayed. On some systems, the transparent pixel index is a constant. On other hardware, the transparent index is a function of the underlying Window (GLX_LEVEL <= 0). Applications may use glXGetTransparentIndexSUN to determine whether a transparent index is available for a particular pair of windows and to determine the value of the tran- sparent index. If glXGetTransparentIndexSUN returns 1 after being called with underlay equal to a valid window, then the transparent index is valid only for underlay. The underlay Window must have been previously made the current GLXDrawable of the thread. If a Window other than underlay is directly beneath overlay the results of drawing with the transparentIndex are unde- fined. If glXGetTransparentIndexSUN returns 1 when the underlay argument is set to None, the transparentIndex is valid for all underlay windows. ERRORS A BadDrawable error is returned if overlay is not a valid Window or if underlay is not a valid Window (except None). NOTES When the transparent index is valid only for a particular underlay window, applications should follow the following guidelines to insure proper operation: 1) It is the application's responsibility to ensure that the only window ever underneath overlay is underlay. 2) Ideally, overlay should be created as a child of underlay with the same size and shape. The application should reshape the overlay window whenever the underlay window is reshaped. This ensures that the transparent index makes the overlay transparent.
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