[vertex]


layout(location=0) in highp vec4 vertex_attrib;
layout(location=4) in vec2 uv_in;

out vec2 uv_interp;


void main() {

	uv_interp = uv_in;
	gl_Position = vertex_attrib;
}

[fragment]

//#define QUALIFIER uniform // some guy on the interweb says it may be faster with this
#define QUALIFIER const
#ifdef USE_25_SAMPLES

const int kernel_size=25;

QUALIFIER vec2 kernel[25] = vec2[] (
vec2(0.099654,0.0),
vec2(0.001133,-3.0),
vec2(0.002316,-2.52083),
vec2(0.00445,-2.08333),
vec2(0.008033,-1.6875),
vec2(0.013627,-1.33333),
vec2(0.021724,-1.02083),
vec2(0.032542,-0.75),
vec2(0.04581,-0.520833),
vec2(0.0606,-0.333333),
vec2(0.075333,-0.1875),
vec2(0.088001,-0.0833333),
vec2(0.096603,-0.0208333),
vec2(0.096603,0.0208333),
vec2(0.088001,0.0833333),
vec2(0.075333,0.1875),
vec2(0.0606,0.333333),
vec2(0.04581,0.520833),
vec2(0.032542,0.75),
vec2(0.021724,1.02083),
vec2(0.013627,1.33333),
vec2(0.008033,1.6875),
vec2(0.00445,2.08333),
vec2(0.002316,2.52),
vec2(0.001133,3.0)
);

#endif //USE_25_SAMPLES

#ifdef USE_17_SAMPLES

const int kernel_size=17;

QUALIFIER vec2 kernel[17] = vec2[](
vec2(0.197417,0.0),
vec2(0.000078,-2.0),
vec2(0.000489,-1.53125),
vec2(0.002403,-1.125),
vec2(0.009245,-0.78125),
vec2(0.027835,-0.5),
vec2(0.065592,-0.28125),
vec2(0.12098,-0.125),
vec2(0.17467,-0.03125),
vec2(0.17467,0.03125),
vec2(0.12098,0.125),
vec2(0.065592,0.28125),
vec2(0.027835,0.5),
vec2(0.009245,0.78125),
vec2(0.002403,1.125),
vec2(0.000489,1.53125),
vec2(0.000078,2.0)
);

#endif //USE_17_SAMPLES


#ifdef USE_11_SAMPLES

const int kernel_size=11;

QUALIFIER vec2 kernel[kernel_size] = vec2[](
vec2(0.198596,0.0),
vec2(0.0093,-2.0),
vec2(0.028002,-1.28),
vec2(0.065984,-0.72),
vec2(0.121703,-0.32),
vec2(0.175713,-0.08),
vec2(0.175713,0.08),
vec2(0.121703,0.32),
vec2(0.065984,0.72),
vec2(0.028002,1.28),
vec2(0.0093,2.0)
);

#endif //USE_11_SAMPLES


uniform float max_radius;
uniform float camera_z_far;
uniform float camera_z_near;
uniform float unit_size;
uniform vec2 dir;
in vec2 uv_interp;

uniform sampler2D source_diffuse; //texunit:0
uniform sampler2D source_sss; //texunit:1
uniform sampler2D source_depth; //texunit:2

layout(location = 0) out vec4 frag_color;

void main() {

	float strength = texture(source_sss,uv_interp).r;
	strength*=strength; //stored as sqrt

	// Fetch color of current pixel:
	vec4 base_color = texture(source_diffuse, uv_interp);


	if (strength>0.0) {


		// Fetch linear depth of current pixel:
		float depth = texture(source_depth, uv_interp).r * 2.0 - 1.0;
		depth = 2.0 * camera_z_near * camera_z_far / (camera_z_far + camera_z_near - depth * (camera_z_far - camera_z_near));



		float scale = unit_size / depth; //remember depth is negative by default in OpenGL

		// Calculate the final step to fetch the surrounding pixels:
		vec2 step = max_radius * scale * dir;
		step *= strength; // Modulate it using the alpha channel.
		step *= 1.0 / 3.0; // Divide by 3 as the kernels range from -3 to 3.

		// Accumulate the center sample:
		vec3 color_accum = base_color.rgb;
		color_accum *= kernel[0].x;
#ifdef ENABLE_STRENGTH_WEIGHTING
		float color_weight = kernel[0].x;
#endif

		// Accumulate the other samples:
		for (int i = 1; i < kernel_size; i++) {
			// Fetch color and depth for current sample:
			vec2 offset = uv_interp + kernel[i].y * step;
			vec3 color = texture(source_diffuse, offset).rgb;

#ifdef ENABLE_FOLLOW_SURFACE
			// If the difference in depth is huge, we lerp color back to "colorM":
			float depth_cmp = texture(source_depth, offset).r *2.0 - 1.0;
			depth_cmp = 2.0 * camera_z_near * camera_z_far / (camera_z_far + camera_z_near - depth_cmp * (camera_z_far - camera_z_near));

			float s = clamp(300.0f * distance *
					       max_radius * abs(depth - depth_cmp),0.0,1.0);
			color = mix(color, base_color.rgb, s);
#endif

			// Accumulate:
			color*=kernel[i].x;

#ifdef ENABLE_STRENGTH_WEIGHTING
			float color_s = texture(source_sss, offset).r;
			color_weight+=color_s * kernel[i].x;
			color*=color_s;
#endif
			color_accum += color;

		}

#ifdef ENABLE_STRENGTH_WEIGHTING
		color_accum/=color_weight;
#endif
		frag_color = vec4(color_accum,base_color.a); //keep alpha (used for SSAO)
	} else {
		frag_color = base_color;
	}
}