Controlling Overlay Quality In 3D Mode

Controlling overlay quality in 3D mode

Hidden-line removal in Z-buffered 3D graphics presents a problem to the programmer because the edges round elements will look "patchy" if they are drawn (correctly) co-planar with the element infill. Therefore overlay has to be raised slightly towards the observer (in the screen space Z dimension) to lift it above the surrounding elements, and the algorithm which calculates this "Z lift" dimension is usually satisfactory for all normal viewing parameters. However there are a few cases in which it can go wrong:

This image demonstrates the "patchy" overlay that can occur if the "Z lift" dimension is insufficient to raise it above the surrounding element infill. This does not normally happen, but it can occur if:

• Perspective is turned on
• And the perspective distance is very small

To fix this problem use < right ctrl > + < mouse button >. Moving the mouse up the screen will raise the overlay towards you, moving it down away. The mouse button used controls the speed of "Z lift" change:

< Left mouse >	Produces slow change
< Middle mouse >	Moves it more quickly
< Right mouse >	Makes large changes

If you subsequently revert to a more "normal" viewing distance you may need to reset the "Z lift" to get an acceptable image quality.