tjh@bucrf11.bu.edu (Tim Hall) (06/08/91)
On our GTX-B, (no destination alpha planes) specifing a different alpha value at each vertex of a polygon doesn't seem to work. (This is, of course, using an apprpreate "blendfunction") For example, the polygon should go from being completely transparent at one vertex to completely opaque at the other vertex. The GL seems to want to interpolate the alpha values when the alpha values of the first two verticies differ. It's close, but no cigar. Changing the alpha values on subsequent verticies has no effect. So is it the GL or should I get my eyes checked? Oh, the machine is running 3.3.2. -- -Tim Hall tjh@bu-pub.bu.edu Across the sea, lies the fountain of renewal, where you will see, the whole cause of your loneliness, can be measured in dreams... -DCD
kurt@cashew.asd.sgi.com (Kurt Akeley) (06/12/91)
In article <83407@bu.edu>, tjh@bucrf11.bu.edu (Tim Hall) writes: |> On our GTX-B, (no destination alpha planes) specifing a different alpha |> value at each vertex of a polygon doesn't seem to work. (This is, of course, using an apprpreate "blendfunction") For example, the polygon should go from being completely transparent at one vertex to completely opaque at the other vertex. The GL seems |> to want to interpolate the alpha values when the |> alpha values of the first two verticies differ. It's close, but no cigar. Changing the alpha values on subsequent verticies has no effect. So is it the |> GL or should I get my eyes checked? |> |> Oh, the machine is running 3.3.2. Iris GT and early model GTX machines do not interpolate alpha correctly when filling smooth shaded polygons. Alpha is interpolated along polygon edges, but not within vertical spans. The error is in hardware, not microcode, so it will not be corrected by future software releases. Sorry. -- Kurt