uniform mat4 uModelViewProjection;
uniform mat4 uModelView;
uniform mat3 uNormalMatrix;

attribute vec3 aPosition;
attribute vec3 aNormal;
attribute vec2 aTexCoord;

varying vec3 vPosition;
varying vec3 vNormal;
varying vec2 vTexCoord;

void main() {
	gl_Position = uModelViewProjection * vec4(aPosition, 1.0);
	vPosition = (uModelView * vec4(aPosition, 1.0)).xyz;
	vNormal = normalize(uNormalMatrix * aNormal);
	vTexCoord = aTexCoord;
}

uniform sampler2D uTexture;

// the lightsource described by position and radius
uniform vec4 uLightsource;
vec3 lsPosition = uLightsource.xyz;
float lsRadius = uLightsource.w;

// each shadow volume is described by position (xyz) and radius (w) of the occluder packed into a single vec4
const int shadowMaxCount = 5;
uniform vec4 uShadows[shadowMaxCount];
uniform int uShadowCount;

varying vec3 vPosition;
varying vec3 vNormal;
varying vec2 vTexCoord;


const vec3 cAmbient = vec3(0.025,0.025,0.025);

// simple local diffuse per-pixel lighting
float diffuseFactor() {
	vec3 lightDir = normalize(lsPosition-vPosition);
	vec3 normal = normalize(vNormal);
	return max(dot(lightDir, normal), 0.0);
}

// process all shadow volumes
float shadowFactor() {
	float s = 1.0;
	// iterate all shadow volumes
	for (int i=0; i<uShadowCount; ++i) {
		// extract data
		vec4 occluder = uShadows[i];
		vec3 ocPosition = occluder.xyz;
		float ocRadius = occluder.w;

		// project fragment (vPosition) on the cone axis => F_
		vec3 nvLO = ocPosition - lsPosition;
		float dLO = length(nvLO);
		nvLO /= dLO;
		vec3 vLF = vPosition - lsPosition;
		float dLF_ = dot(vLF, nvLO);
		if (dLF_ < dLO) {
			// fragment before occluder => no shadow
			continue; 
		}
		vec3 F_ = lsPosition + dLF_ * nvLO;
		float rF = distance(F_, vPosition);

		// compute outer and inner radius at F_
		float rF_outer = (ocRadius + lsRadius) * (dLF_ / dLO) - lsRadius;
		if (rF >= rF_outer) {
			// outside the outer cone => no shadow
			continue;
		} 
		float rF_inner = (ocRadius - lsRadius) * (dLF_ / dLO) + lsRadius;
		if (rF_inner >= rF) {
			// inside the inner cone => full shadow
			return 0.0; 
		}
		else if (rF_inner >= 0.0 || rF >= -rF_inner) {
			// soft shadow, linear interpolation
			s *= (rF - rF_inner) / (rF_outer - rF_inner);
		}
		else {
			// light from both sides of the occluder
			s *= (-2.0*rF_inner) / (rF_outer - rF_inner);
		}
	}
	return s;
}

void main() {
	vec3 texcolor = texture2D(uTexture, vTexCoord).xyz;
	gl_FragColor.xyz = cAmbient * texcolor;
	float lightFactor = diffuseFactor();
	if (lightFactor > 0.004) {
		// don't compute shadows for fragments that are already dark from local lighting
		lightFactor *= shadowFactor();
	}
	gl_FragColor.xyz += texcolor * lightFactor;
	gl_FragColor.w = 1.0;
}