Trail dewiggle

When using a particle trail with lots of sections, you may see an unintended wiggling artifact caused by naive interpolation. Here I use a trick to improve the interpolation by extracting the size of the TrailMesh encoded in length(VERTEX.xz). Apply the shader to the draw pass with trails enabled, and comment lines 11/18 to compare.

NOTE: Ribbon trails are only available in Godot 4, but you can adapt the trick to work in combo with my own trail technique for Godot 3

Shader code

shader_type spatial;

render_mode unshaded,blend_add,cull_disabled,particle_trails;

uniform sampler2D texture_albedo : source_color;

varying float scale_interp;
void vertex() {
	// dewiggle
	scale_interp = length(VERTEX.xz);
	UV *= scale_interp;
}

void fragment() {
	vec2 base_uv = UV;
	
	// dewiggle
	base_uv /= scale_interp;
	
	vec4 albedo_tex = texture(texture_albedo,base_uv);
	ALBEDO = COLOR.rgb * albedo_tex.rgb;
	ALPHA *= COLOR.a * albedo_tex.a;
}

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