Z-Epsilon is approximately the smallest Z value recognized by the graphics stack to make a difference in Z positioning. Z-Epsilon depends on the current projection matrix, i.e. Z distance of the viewer. See http://www.sjbaker.org/steve/omniv/love_your_z_buffer.html z_epsilon = z * z / ( zNear * ( 1 << zBits ) - z ); We utilize Z-Epsilon as the smallest offset between the button background shape and the label text. We also utilize Z-Epsilon as the offset to elevate the active (selected) shape (add z-offset) and select (pick) in Z descending order (Bug 1454).
bc4a97a3751b32a7825a41481959f04ff3efb3d2 GraphUI Scene: Expose Z-Epsilon API for default and current PMVMatrixSetup values; Button add Z-Epsilon API for ctor and setLabelZOffset(..) +++ d5b17eddf7e7f1c33b269a3a2ed8eca959c6d639 GraphUI Enhance: API doc; Scene/Button Z-offset and -epsilon; Push temp AffineTransform to local method; Simplify BaseButton setCorner(0) -> setPerp(); Protected abstract ctor +++ ..