Around 10 o'clock on May 12, [EMAIL PROTECTED] wrote:
> Isn't it less misleading to say partial coverage is indistinguishable > from a transmissivity less than one. Or partial coverage is indistinguishable from partial opacity, which is more-or-less what alpha measures. > Translucency usually implies some degree of dispersive effects. E.g. > translucent objects cause blurring of the background object, not merely > reduced light transmission. That would be fun to implement, but it is a global effect rather than a purely local effect. As we don't (currently) expect hardware to offer anything like this, there's no real reason to put it into the X server. XIE provides some of this functionality, but the lack of acceleration made that extension worthless -- the extension could not ever gain traction because applications needed to provide a client-side implementation for servers that didn't offer the extension, and the extension offered no performance benefits. Hence, the extra work needed to use the extension made no sense. > The OpenGL specification states that alpha shall implement transmissivity, > but the DirectX specification states that alpha implements voltage > interpolation. Since voltage interpolation is immensely easier to > implement in hardware, all of the affordable PC graphics cards only support > voltage interpolation. Apparantly some PC graphics cards have started providing gamma-corrected compositing, which provides (slightly) improved appearance, especially for partial-pixel coverage approximations. AA text suffers badly under voltage interpolation; I've already planned on adding gamma correction to the Render extension to improve the appearance of light text over a dark background. > If we wanted to put in the effort, Render could define a software > implementation (with some new pixrect definitions required) that truly > did implement transmissivity computations. Anything we can reasonably expect some common hardware to implement is certainly a candidate for inclusion in the extension, other operations only move computation from client to server offering little in the way of significant performance improvements. But, it certainly would be fun to design such a system and implement it on the client side as a part of a more comprehensive visually modelled graphics system. Keith Packard XFree86 Core Team HP Cambridge Research Lab _______________________________________________ Render mailing list [EMAIL PROTECTED] http://XFree86.Org/mailman/listinfo/render
