Fix massive performance hit due to enabling collision

[k0T0z]

Fixes #83744

Do we need to modify this patch #76598?

[RPicster]

Looks good to me, I also tested the PR and it works as expected.
In my game it even gave a noticable performance increase.

[k0T0z]

@RPicster Great, I am gonna add a comment for explanation now. Please approve that we need to make any changes to #76598 as well.

[k0T0z]

What I see is that this snippet is a simple calculation going on there, so why there's a massive performance hit happening here? Maybe the rand_from_seed() function? dk for sure

if (!COLLIDED) {
	float vel_mag = length(VELOCITY);
	float vel_infl = clamp(mix(turbulence_influence_min, turbulence_influence_max, rand_from_seed(alt_seed)) * turbulence_influence, 0.0, 1.0);
	VELOCITY = mix(VELOCITY, normalize(noise_direction) * vel_mag * (1.0 + (1.0 - vel_infl) * 0.2), vel_infl);
}

EDIT: I noticed the mix() function here, I read it min(), dk what it means. If someone can explain why this snippet causes these big differences in FPS, I would really appreciate it.

[clayjohn]

What I see is that this snippet is a simple calculation going on there, so why there's a massive performance hit happening here? Maybe the rand_from_seed() function? dk for sure

if (!COLLIDED) {
	float vel_mag = length(VELOCITY);
	float vel_infl = clamp(mix(turbulence_influence_min, turbulence_influence_max, rand_from_seed(alt_seed)) * turbulence_influence, 0.0, 1.0);
	VELOCITY = mix(VELOCITY, normalize(noise_direction) * vel_mag * (1.0 + (1.0 - vel_infl) * 0.2), vel_infl);
}

EDIT: I noticed the mix() function here, I read it min(), dk what it means. If someone can explain why this snippet causes these big differences in FPS, I would really appreciate it.

Godot detects when the COLLIDED keyword is used. If it's used anywhere in the shader then Godot will generate the screen space SDF for collisions. The performance cost is not from the shader itself, but from the cost of generating the SDF. If the SDF is used by another effect, then using COLLIDED wouldn't add additional cost

[k0T0z]

@clayjohn I noticed COLLIDED is only used in branches where the collision is enabled, yeah, it's hard to know about Godot detects any use of COLLIDED anywhere alone, I get it now thanks for clarifying 👌

[akien-mga]

Do we need to modify this patch #76598?

WDYT @Calinou @RPicster?

[RPicster]

I don't know if that was the root of the cause of the original reason for the performance problem. Turbulence will always come at an increased cost. So eventually rather be safe than sorry with the documentation?

[Calinou]

I don't know if that was the root of the cause of the original reason for the performance problem. Turbulence will always come at an increased cost. So eventually rather be safe than sorry with the documentation?

Indeed, we still expect turbulence to take up a significant amount of GPU time on integrated graphics.

[akien-mga]

Thanks!