George, I think your shader is the problem here (although I've not got the plugin installed to be sure). You're setting the vertex colours to red with alpha at 0.0, then in the fragment shader you're ADDING the vertex colour to the texture colour. This totally messes up the colours, and of course if you change the alpha value in the vertex shader to 1.0 you get 1.0 + texture alpha, which means the whole quad is opaque.
The 'blobby' look is probably down to alpha premultiplication (or lack of). Try something like: vec4 output = color + Color; // urgh at the naming there! ;D output.rgb *= output.a; return output; Maybe that will fix it. Chris On 20 Jun 2010, at 08:37, George Toledo wrote: > > > I hope I'm asking this question in the right place, and there are sort of two > separate issues at play - alpha calculation in GLSL shaders, and then > Over/Alpha Blend modes. > > Is there support for alpha in GLSL shaders in QC? > > In a vertex shader, I have the following line: > > Color = vec4(surfaceColor.rgb, 1.0); > > When I change it to: > > Color = vec4(surfaceColor.rgb, 0.0); > > I see an unexpected difference in the alpha content on the final textured > object in Over mode. While I do see it change from "quad" look to having > areas of obvious transparency, it looks clearly wrong. SO, I had the bright > idea to change the line... > > When I change it to : > > Color = vec4(surfaceColor.rgba); > > I don't see any errors, but I see no difference when I change Opacity/Alpha > value on the actual shader input for the surfaceColor. I would think that > would be the "fix". However, it doesn't work completely (the color of the > texture looks "blobby" in areas where alpha should be fading....more > smoothly?) > > The only workaround I've found is to use actual alpha blending on the > renderer, in this case, by using the Kineme AlphaBlend.plugin. > > Then, I see a clear difference between the two different alpha channel > values, and by setting alpha to 0 in the shader, things work as expected. > > This is a sample composition; I apologize, because it's sort of non-standard, > because one would need to install the AlphaBlend.plugin for this to render as > I would expect it should in QC normally (in Over mode). I understand if no > one is thrilled to look at this because of that, but it's not a question > about a bug being caused by a 3rd party plugin (in this case, it's the only > way to see what I expect to in Over with the shader at an alpha of 0, or with > the surfaceColor.rgba line). > > -George Toledo > > <Shaded and Textured Particles Alpha Blend.qtz> > _______________________________________________ > Do not post admin requests to the list. They will be ignored. > Quartzcomposer-dev mailing list (Quartzcomposer-dev@lists.apple.com) > Help/Unsubscribe/Update your Subscription: > http://lists.apple.com/mailman/options/quartzcomposer-dev/psonice%40gmail.com > > This email sent to pson...@gmail.com _______________________________________________ Do not post admin requests to the list. They will be ignored. Quartzcomposer-dev mailing list (Quartzcomposer-dev@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/quartzcomposer-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
