Fix bloom artifacts appearing due to bad specular data

[Christopher-Hayes]

Description

Fixes black square artifacts appearing on screen when the Bloom or Dof effects were used with the CameraFrame script. This bug was only reproduced on Ubuntu with an nvidia GPU.

Solution

This patch adds a clamp to the fresnelSchlick.js functions, getFresnel() and getFresnelCC(), to avoid bad specular values.

Explanation

I still don't think I'm 100% sure why it was happening, but from what I can tell:

1. When the angle of light and the camera were exactly parallel it would cause this dot product calculation to be -1.
   

   engine/src/scene/shader-lib/chunks/lit/frag/pass-forward/litForwardBackend.js

   Lines 106 to 114 in 49ffb62

   	dReflection.rgb *= getFresnel(
   	dot(dViewDirW, litArgs_worldNormal),
   	litArgs_gloss,
   	litArgs_specularity
   	#if defined(LIT_IRIDESCENCE)
   	, iridescenceFresnel,
   	litArgs_iridescence_intensity
   	#endif
   	);

2. With the current implementation, a cosTheta of -1 should not break anything. max() would set it to 0.0 and the function should work okay.
   

   engine/src/scene/shader-lib/chunks/lit/frag/fresnelSchlick.js

   Lines 1 to 21 in 49ffb62

   	export default /* glsl */`
   	// Schlick's approximation
   	vec3 getFresnel(
   	float cosTheta,
   	float gloss,
   	vec3 specularity
   	#if defined(LIT_IRIDESCENCE)
   	, vec3 iridescenceFresnel,
   	float iridescenceIntensity
   	#endif
   	) {
   	float fresnel = pow(1.0 - max(cosTheta, 0.0), 5.0);
   	float glossSq = gloss * gloss;
   	vec3 ret = specularity + (max(vec3(glossSq), specularity) - specularity) * fresnel;
   	#if defined(LIT_IRIDESCENCE)
   	return mix(ret, iridescenceFresnel, iridescenceIntensity);
   	#else
   	return ret;
   	#endif
   	}

3. But, for whatever reason on certain devices it was causing getFresnel() to return a bad specular value.
4. This seems limited to only a pixel or two, but bloom upscaling makes these artifacts a lot more noticeable.

Before vs After

(Note that the flashing is more visible in-person, the low-FPS recording hides it somewhat)

Screencast.From.2025-04-25.03-26-28.mp4

Testing

Project for testing: https://playcanvas.com/editor/scene/2210459

Fixes #7492

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[Copilot]

Pull Request Overview

A patch to fix bloom artifacts by clamping specular values in shader functions.

• Modified getFresnel() to use clamp instead of max for cosTheta
• Modified getFresnelCC() in a similar fashion to ensure values remain within [0, 1]

[mvaligursky]

Looks great, thanks!