Using Existing Xlib Pixel Transfer Routines

The Xlib pixel transfer routines XGetImage, XCopyArea, and XCopyPlane can also be used with transparent overlay windows.

XGetImage

On non-overlay drawables, the XGetImage routine works as defined in the X11 specification. The same is true for overlay windows, with the exception that, on these windows, the color information returned for transparent pixels is undefined. Clients who simply want to retrieve the display colors for a region on the screen should use XReadScreen.

XCopyArea and XCopyPlane

When both the source and destination drawables are non-overlay, the XCopyArea and XCopyPlane routines work as defined in the X11 specification. However, note the following for the cases in which either the source or the destination drawable is an overlay window.

• When the source drawable is overlay and the destination drawable is non-overlay, only the color information is copied; the paint type information in the source is ignored. Color information for transparent pixels is undefined.

• When the source drawable is non-overlay and the destination drawable is overlay, the copy is performed as the paint type in the GC indicates. If the paint type is XSolarisOvlPaintOpaque, the color information is copied into the destination with opaque paint. If the paint type is XSolarisOvlPaintTransparent, the color information is ignored, and the destination pixels are transparent.

• When both the source drawable and destination drawable are overlay, the paint type of the source is ignored, and this behaves as if the source were not an overlay. If copying both color and paint type information is the desired result, use XSolarisOvlCopyAreaAndPaintType.