CopyPass: Assume premultipliedAlpha is set to true. #24277
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| @@ -105,7 +105,8 @@ class OutlinePass extends Pass { | |||
| blending: NoBlending, | |||
| depthTest: false, | |||
| depthWrite: false, | |||
| transparent: true | |||
| transparent: true, | |||
| premultipliedAlpha: true | |||
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Setting NoBlending and premultipliedAlpha: true and transparent: true at the same time?
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@Mugen87 I appreciate your desire to work on this. I just think it is going to take a lot of thought to get opacity properly-supported in EffectComposer.
The transparent flag is for user convenience, in lieu of having to set the blending. I am not sure it is wise to be setting both. ( Is the transparent flag needed for the transparent rendering group? ).
Is premultipliedAlpha even supported with NoBlending?
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Setting NoBlending and premultipliedAlpha: true and transparent: true at the same time?
My point is: Since the shader implementation assumes premultiplied alpha, I would suggest to always set premultipliedAlpha to true for clarity.
Whether or not all combinations of transparent and blending make sense is something I would tackle in a different issue/PR.
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Since the shader implementation assumes premultiplied alpha
The drawing buffer has premultiplied alpha, but the output of the shader may or may not have it.
You only need to set material.premultipliedAlpha if it is required to get the correct answer. Setting it when it is not needed just causes more confusion.
.premultipliedAlpha is a flag, just like transparent, to guide the renderer in setting the correct blending function. It only applies to the built-in blending functions.
.premultipliedAlpha means the output of the shader has RGB multiplied by alpha. In that case, it triggers the renderer to select a blending function different from the typical one.
.premultipliedAlpha does not apply when NoBlending is set.
To understand these concepts, I'd start with understanding the setBlending() function in WebGLState.js.
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I'm aware how premultipliedAlpha is used in WebGLState. I'm just the opinion that less errors occur if premultipliedAlpha is always set to true for this particular case. Especially since nothing breaks even when no alpha blending is used.
In other words: We should not expect that users enable premultipliedAlpha if they blend the result of a copy pass. webgl_postprocessing_backgrounds shows that even examples don't do this right.
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Closing in favor of #26179. |
Fixed #19531.
Description
Reverts #23671 and ensures copy materials always set
premultipliedAlphatotrue. The PR also introducesCopyPassfor an easier usage on app level.Motivation of this change is outlined here: #19531 (comment)