GPUParticles3D billboarding is affected by particle's global rotation when precision=double

[cridenour]

Godot version

v4.0.2.stable.custom_build [285ca4637]

System information

Windows 10, Forward+

Issue description

With #76003 and #75462 I thought my particle issues were solved, but in testing I've noticed more billboard strangeness. Finally debugged it to the global rotation of the particles node.

This issue is not present in non-double precision builds.

Steps to reproduce

1. Create a GPUParticles3D in a double precision build
2. Set billboarding in the material
3. Rotate the particles node or its parent

Minimal reproduction project

double-particles-2.zip

[cridenour]

Wondering / hoping if #72638 will improve this situation. Will take a closer look this weekend if I get a chance.

[cridenour]

As noted in #89020 - can be worked around by enabled Rotate Y in the process material.

[ecmjohnson]

This issue is caused by the following block in the shader code scene_forward_clustered.glsl after the #CODE : VERTEX:

godot/servers/rendering/renderer_rd/shaders/forward_clustered/scene_forward_clustered.glsl

Lines 400 to 415 in f2045ba

	#ifdef USE_DOUBLE_PRECISION
	// We separate the basis from the origin because the basis is fine with single point precision.
	// Then we combine the translations from the model matrix and the view matrix using emulated doubles.
	// We add the result to the vertex and ignore the final lost precision.
	vec3 model_origin = model_matrix[3].xyz;
	if (is_multimesh) {
	vertex = mat3(matrix) * vertex;
	model_origin = double_add_vec3(model_origin, model_precision, matrix[3].xyz, vec3(0.0), model_precision);
	}
	vertex = mat3(inv_view_matrix * modelview) * vertex;
	vec3 temp_precision; // Will be ignored.
	vertex += double_add_vec3(model_origin, model_precision, scene_data.inv_view_matrix[3].xyz, view_precision, temp_precision);
	vertex = mat3(scene_data.view_matrix) * vertex;
	#else
	vertex = (modelview * vec4(vertex, 1.0)).xyz;
	#endif

If you remove the USE_DOUBLE_PRECISION branch, then this issue goes away.