The renderer ignores adjustments to Color(3)

Bugs
,
1

I am on a Mac, Build 2025.32820

I believe this is a bug, but please correct me if I’m mistaken.

alpha render bug.toe (227.9 KB)

I have a Color attribute applied to some geometry using a Lookup Texture POP. When I adjust the alpha value in the associated Ramp TOP (affecting Color(3)), the resulting adjusted transparency is correctly rendered. However, when I adjust Color(3) in a Math POP, no change in the rendered output is effected. I can adjust RGB (as Color(0), Color(1), and Color(2)) in the Math POP, and the colors render as expected. Only the alpha channel fails to have a result.

To verify the data itself, I inserted a POP to DAT after the Math POP. It shows that Color(3) is being updated correctly, whether by adjusting the Ramp TOP, or by adjusting the Math POP. In addition, modifying Color(0), Color(1), and Color(2) in the same Math POP correctly affects the rendered RGB output. Only changes to Color(3) appear to be ignored by the renderer.

I confirm this issue applies to (at least) rendering with the Line MAT and the Phong MAT.

2

Hello @etsim

Blending is not enabled on the Phong MAT at all. Does enabling Blending with Separate Alpha Function, and using Source Alpha for Source Color, give you the expected result? By the way, when blending, the alpha values should not exceed one.

image
image1302×715 136 KB

1 Like
3

Thank you! Using Source Alpha for Source Color worked, so that now adjusting Color(3) in the Math POP is respected by the renderer. FYI this works for me regardless of whether or not I have enabled Separate Alpha Function.

I still don’t understand why Color(3) as adjusted at the Ramp TOP + Texture Lookup POP is treated differently than Color(3) as adjusted by the Math POP, but at least I can get the result I want now. Thank you again!

4

Also, just for clarity, although my example file had Blending disabled, my original issue of disparate treatment of Color(3) does indeed apply to the case with Blending (Transparency) set to On, and with Source Color set to One.