NormalMapNode: Fix dpdx and dpdy called from non-uniform control flow

[sunag]

Related issue: #24059 (comment)

Description

I believe that this conditional was inserted to optimize the shader, although conditionals are always expensive for GPU.

Code without conditionals is understood as uniform control flow and with conditional non-uniform control flow.
Ref: https://www.khronos.org/registry/OpenGL/specs/gl/GLSLangSpec.4.50.pdf - page 23

This fix WebGPU warning: 'dpdy' must only be called from uniform control flow and follow the approach closer of http://www.thetenthplanet.de/archives/1180

I wounder if this is not responsible for bugs in WebGL using perturbNormal2Arb too!?...

This contribution is funded by Google via Igalia

[Mugen87]

I wounder if this is not responsible for bugs in WebGL using perturbNormal2Arb too!?...

On what line of code in normalmap_pars_fragment are you referring to?

[LeviPesin]

I think

three.js/src/renderers/shaders/ShaderChunk/normalmap_pars_fragment.glsl.js

Line 38 in 21686c6

float scale = ( det == 0.0 ) ? 0.0 : faceDirection * inversesqrt( det );

.

[sunag]

On what line of code in normalmap_pars_fragment are you referring to?

The line was the mentioned by @LeviPesin, I say this mainly because of the workaround for Adreno