Updated: Faux Vertex Lighting

* NEW *

• Segment size parameter
• Light falloff and range parameters
• Flip axis toggles

Lights need to be set at 1 attenuation for the effect to work properly, and model UVs need to be well-formed

This is a novel attempt at lighting that is identical to the real thing with a couple of added benefits for lazy people like me.

Here are some features:

• Utilizes scene lights
• Simulates subdivided surfaces for more detailed lighting without the need for more vertices
  • Subdivisions are not constrained to triangle boundaries, so they aren’t strictly accurate
  • Removing this would result in an authentic implementation for better or for worse

Thanks to Momonyaro for testing on their project.

Shader code

shader_type spatial;
render_mode skip_vertex_transform;

varying vec3 sfcPosVS;
varying vec3 sfcPosLS;
varying vec3 sfcNmlLS;
varying vec3 sfcRtLS;
varying vec3 sfcUpLS;

vec3 cvtSpcPos(vec3 v, mat4 m) {
	return (m * vec4(v, 1.)).xyz;
}

vec3 cvtSpcDir(vec3 v, mat4 m) {
	return normalize((m * vec4(v, 0.0)).xyz);
}

float quadraticBezierFalloff(float t, float q, float p, float s) {
	return (q + 1. - t * (p - q)) + t * ((q + t * (s - q)) - q + 1. - t * (p - q));
}

uniform sampler2D albedo;
uniform float range;
uniform float falloff;
uniform float segment_scale;
uniform bool flip_x;
uniform bool flip_y;

void vertex() {
	sfcPosLS = VERTEX;
	sfcNmlLS = NORMAL;
	sfcRtLS = segment_scale * TANGENT * (2. * float(flip_x) - 1.);
	sfcUpLS = segment_scale * cross(TANGENT,NORMAL) * (2. * float(flip_y) - 1.);
	
	VERTEX = cvtSpcPos(VERTEX,MODELVIEW_MATRIX);
	NORMAL = cvtSpcDir(NORMAL,MODELVIEW_MATRIX);
	sfcPosVS = VERTEX;
}

void fragment() {
	ALBEDO = texture(albedo,UV).rgb;
}

void light() {
	vec3 lgtPosVS = (LIGHT / ATTENUATION) + sfcPosVS;
	vec3 lgtPosWS = cvtSpcPos(lgtPosVS,INV_VIEW_MATRIX);
	
	vec3 uv3d = vec3(
		dot(sfcPosLS,sfcRtLS),
		dot(sfcPosLS,-sfcUpLS),
		dot(sfcPosLS,sfcNmlLS)
	);
	
	vec3 uvQtz = vec3(
		floor(dot(sfcPosLS,sfcRtLS)),
		floor(dot(sfcPosLS,-sfcUpLS)),
		dot(sfcPosLS,sfcNmlLS)
	);
	
	vec3 uvFrc = fract(uv3d);
	
	vec3 tstPosLS = cvtSpcPos(lgtPosWS,inverse(MODEL_MATRIX));
	
	vec3 tstPos2D = vec3(
		dot(tstPosLS,sfcRtLS),
		dot(tstPosLS,-sfcUpLS),
		dot(tstPosLS,sfcNmlLS)
	);
	
	vec3 prjPosUV = tstPos2D;

	float dst00 = clamp(-quadraticBezierFalloff(distance(prjPosUV,uvQtz) * range,falloff,1.,0.),0.,1.);
	float dst01 = clamp(-quadraticBezierFalloff(distance(prjPosUV,uvQtz + vec3(0.,1.,0.)) * range,falloff,1.,0.),0.,1.);
	float dst10 = clamp(-quadraticBezierFalloff(distance(prjPosUV,uvQtz + vec3(1.,0.,0.)) * range,falloff,1.,0.),0.,1.);
	float dst11 = clamp(-quadraticBezierFalloff(distance(prjPosUV,uvQtz + vec3(1.,1.,0.)) * range,falloff,1.,0.),0.,1.);
	
	float final;
	
	if (uvFrc.x > uvFrc.y) {
		final = 
			(1. - uvFrc.x) * dst00 + 
			(uvFrc.x - uvFrc.y) * dst10 + 
			uvFrc.y * dst11; }
	else {
		final = 
			(1. - uvFrc.y) * dst00 + 
			(uvFrc.y - uvFrc.x) * dst01 + 
			uvFrc.x * dst11;
	}
	
	float sfcAngMlt = clamp(dot(LIGHT,NORMAL),0.,1.);
	float atnMod = clamp(ATTENUATION,0.,1.);
	
	DIFFUSE_LIGHT += atnMod * LIGHT_COLOR * clamp(1. - final,0.,1.) * sfcAngMlt;
}