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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