/** 
 * @file sunLightSSAOF.glsl
 *
 * Copyright (c) 2007-$CurrentYear$, Linden Research, Inc.
 * $License$
 */
 
#version 120

#extension GL_ARB_texture_rectangle : enable

//class 1 -- no shadow, SSAO only

uniform sampler2DRect depthMap;
uniform sampler2DRect normalMap;
uniform sampler2D noiseMap;

uniform sampler2D		lightFunc;


// Inputs
uniform mat4 shadow_matrix[6];
uniform vec4 shadow_clip;
uniform float ssao_radius;
uniform float ssao_max_radius;
uniform float ssao_factor;
uniform float ssao_factor_inv;

varying vec2 vary_fragcoord;
varying vec4 vary_light;

uniform mat4 inv_proj;
uniform vec2 screen_res;

uniform float shadow_bias;
uniform float shadow_offset;

vec4 getPosition(vec2 pos_screen)
{
	float depth = texture2DRect(depthMap, pos_screen.xy).a;
	vec2 sc = pos_screen.xy*2.0;
	sc /= screen_res;
	sc -= vec2(1.0,1.0);
	vec4 ndc = vec4(sc.x, sc.y, 2.0*depth-1.0, 1.0);
	vec4 pos = inv_proj * ndc;
	pos /= pos.w;
	pos.w = 1.0;
	return pos;
}

//calculate decreases in ambient lighting when crowded out (SSAO)
float calcAmbientOcclusion(vec4 pos, vec3 norm)
{
	float ret = 1.0;
	
	float dist = dot(pos.xyz,pos.xyz);
	
	if (dist < 64.0*64.0)
	{
		vec2 kern[8];
		// exponentially (^2) distant occlusion samples spread around origin
		kern[0] = vec2(-1.0, 0.0) * 0.125*0.125;
		kern[1] = vec2(1.0, 0.0) * 0.250*0.250;
		kern[2] = vec2(0.0, 1.0) * 0.375*0.375;
		kern[3] = vec2(0.0, -1.0) * 0.500*0.500;
		kern[4] = vec2(0.7071, 0.7071) * 0.625*0.625;
		kern[5] = vec2(-0.7071, -0.7071) * 0.750*0.750;
		kern[6] = vec2(-0.7071, 0.7071) * 0.875*0.875;
		kern[7] = vec2(0.7071, -0.7071) * 1.000*1.000;

		vec2 pos_screen = vary_fragcoord.xy;
		vec3 pos_world = pos.xyz;
		vec2 noise_reflect = texture2D(noiseMap, vary_fragcoord.xy/128.0).xy;
		
		float angle_hidden = 0.0;
		int points = 0;
		
		float scale = min(ssao_radius / -pos_world.z, ssao_max_radius);
		
		// it was found that keeping # of samples a constant was the fastest, probably due to compiler optimizations (unrolling?)
		for (int i = 0; i < 8; i++)
		{
			vec2 samppos_screen = pos_screen + scale * reflect(kern[i], noise_reflect);
			vec3 samppos_world = getPosition(samppos_screen).xyz; 
			
			vec3 diff = pos_world - samppos_world;
			float dist2 = dot(diff, diff);
			
			// assume each sample corresponds to an occluding sphere with constant radius, constant x-sectional area
			// --> solid angle shrinking by the square of distance
			//radius is somewhat arbitrary, can approx with just some constant k * 1 / dist^2
			//(k should vary inversely with # of samples, but this is taken care of later)
			
			//if (dot((samppos_world - 0.05*norm - pos_world), norm) > 0.0)  // -0.05*norm to shift sample point back slightly for flat surfaces
			//	angle_hidden += min(1.0/dist2, ssao_factor_inv); // dist != 0 follows from conditional.  max of 1.0 (= ssao_factor_inv * ssao_factor)
			angle_hidden = angle_hidden + float(dot((samppos_world - 0.05*norm - pos_world), norm) > 0.0) * min(1.0/dist2, ssao_factor_inv);
			
			// 'blocked' samples (significantly closer to camera relative to pos_world) are "no data", not "no occlusion" 
			points = points + int(diff.z > -1.0);
		}
		
		angle_hidden = min(ssao_factor*angle_hidden/float(points), 1.0);
		
		ret = (1.0 - (float(points != 0) * angle_hidden));
		ret += max((dist-32.0*32.0)/(32.0*32.0), 0.0);
	}
	
	return min(ret, 1.0);
}

void main() 
{
	vec2 pos_screen = vary_fragcoord.xy;
	
	//try doing an unproject here
	
	vec4 pos = getPosition(pos_screen);
	
	vec3 norm = texture2DRect(normalMap, pos_screen).xyz;
	norm = vec3((norm.xy-0.5)*2.0,norm.z); // unpack norm
		
	gl_FragColor[0] = 1.0;
	gl_FragColor[1] = calcAmbientOcclusion(pos, norm);
	gl_FragColor[2] = 1.0; 
	gl_FragColor[3] = 1.0;
}