This patch aims to add a Holdout blend mode for grease pencil layers. It functions as a subtract blend mode that is transparent itself.
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It functions as a subtract blend mode that is transparent itself.
Holdout is not a subtract blend mode. It's a mix between the destination color and zero, with the source alpha as the mix factor.
Which boils down to dst.rgba = dst.rgba * (1 - src.a).
| source/blender/draw/engines/gpencil/shaders/gpencil_common_lib.glsl | ||
|---|---|---|
| 139 | This does nothing, it's modifying an input parameter. | |
| 140 | Missing break. | |
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Seems you are right. I meant that I thought what I was doing is the same thing as the subtract blend mode but setting the source subtract layer to an alpha of 0.0.
I believe that this may not actually be needed now. In the past I had issues where a subtract layer would show as black instead of transparent and lowering the opacity would remove the subtraction. But it is possible to set a subtract layer to an opacity of 0.0 and have it render transparent and still subtract the other layers.