/**
 * @author Mugen87 / https://github.com/Mugen87
 *
 * References:
 * http://john-chapman-graphics.blogspot.com/2013/01/ssao-tutorial.html
 * https://learnopengl.com/Advanced-Lighting/SSAO
 * https://github.com/McNopper/OpenGL/blob/master/Example28/shader/ssao.frag.glsl
 */

import {
	Matrix4,
	Vector2
} from "../../../build/three.module.js";

var SSAOShader = {

	defines: {
		"PERSPECTIVE_CAMERA": 1,
		"KERNEL_SIZE": 32
	},

	uniforms: {

		"tDiffuse": { value: null },
		"tNormal": { value: null },
		"tDepth": { value: null },
		"tNoise": { value: null },
		"kernel": { value: null },
		"cameraNear": { value: null },
		"cameraFar": { value: null },
		"resolution": { value: new Vector2() },
		"cameraProjectionMatrix": { value: new Matrix4() },
		"cameraInverseProjectionMatrix": { value: new Matrix4() },
		"kernelRadius": { value: 8 },
		"minDistance": { value: 0.005 },
		"maxDistance": { value: 0.05 },

	},

	vertexShader: [

		"varying vec2 vUv;",

		"void main() {",

		"	vUv = uv;",

		"	gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );",

		"}"

	].join( "\n" ),

	fragmentShader: [

		"uniform sampler2D tDiffuse;",
		"uniform sampler2D tNormal;",
		"uniform sampler2D tDepth;",
		"uniform sampler2D tNoise;",

		"uniform vec3 kernel[ KERNEL_SIZE ];",

		"uniform vec2 resolution;",

		"uniform float cameraNear;",
		"uniform float cameraFar;",
		"uniform mat4 cameraProjectionMatrix;",
		"uniform mat4 cameraInverseProjectionMatrix;",

		"uniform float kernelRadius;",
		"uniform float minDistance;", // avoid artifacts caused by neighbour fragments with minimal depth difference
		"uniform float maxDistance;", // avoid the influence of fragments which are too far away

		"varying vec2 vUv;",

		"#include <packing>",

		"float getDepth( const in vec2 screenPosition ) {",

		"	return texture2D( tDepth, screenPosition ).x;",

		"}",

		"float getLinearDepth( const in vec2 screenPosition ) {",

		"	#if PERSPECTIVE_CAMERA == 1",

		"		float fragCoordZ = texture2D( tDepth, screenPosition ).x;",
		"		float viewZ = perspectiveDepthToViewZ( fragCoordZ, cameraNear, cameraFar );",
		"		return viewZToOrthographicDepth( viewZ, cameraNear, cameraFar );",

		"	#else",

		"		return texture2D( depthSampler, coord ).x;",

		"	#endif",

		"}",

		"float getViewZ( const in float depth ) {",

		"	#if PERSPECTIVE_CAMERA == 1",

		"		return perspectiveDepthToViewZ( depth, cameraNear, cameraFar );",

		"	#else",

		"		return orthographicDepthToViewZ( depth, cameraNear, cameraFar );",

		"	#endif",

		"}",

		"vec3 getViewPosition( const in vec2 screenPosition, const in float depth, const in float viewZ ) {",

		"	float clipW = cameraProjectionMatrix[2][3] * viewZ + cameraProjectionMatrix[3][3];",

		"	vec4 clipPosition = vec4( ( vec3( screenPosition, depth ) - 0.5 ) * 2.0, 1.0 );",

		"	clipPosition *= clipW; // unprojection.",

		"	return ( cameraInverseProjectionMatrix * clipPosition ).xyz;",

		"}",

		"vec3 getViewNormal( const in vec2 screenPosition ) {",

		"	return unpackRGBToNormal( texture2D( tNormal, screenPosition ).xyz );",

		"}",

		"void main() {",

		"	float depth = getDepth( vUv );",
		"	float viewZ = getViewZ( depth );",

		"	vec3 viewPosition = getViewPosition( vUv, depth, viewZ );",
		"	vec3 viewNormal = getViewNormal( vUv );",

		" vec2 noiseScale = vec2( resolution.x / 4.0, resolution.y / 4.0 );",
		"	vec3 random = texture2D( tNoise, vUv * noiseScale ).xyz;",

		// compute matrix used to reorient a kernel vector

		"	vec3 tangent = normalize( random - viewNormal * dot( random, viewNormal ) );",
		"	vec3 bitangent = cross( viewNormal, tangent );",
		"	mat3 kernelMatrix = mat3( tangent, bitangent, viewNormal );",

		" float occlusion = 0.0;",

		" for ( int i = 0; i < KERNEL_SIZE; i ++ ) {",

		"		vec3 sampleVector = kernelMatrix * kernel[ i ];", // reorient sample vector in view space
		"		vec3 samplePoint = viewPosition + ( sampleVector * kernelRadius );", // calculate sample point

		"		vec4 samplePointNDC = cameraProjectionMatrix * vec4( samplePoint, 1.0 );", // project point and calculate NDC
		"		samplePointNDC /= samplePointNDC.w;",

		"		vec2 samplePointUv = samplePointNDC.xy * 0.5 + 0.5;", // compute uv coordinates

		"		float realDepth = getLinearDepth( samplePointUv );", // get linear depth from depth texture
		"		float sampleDepth = viewZToOrthographicDepth( samplePoint.z, cameraNear, cameraFar );", // compute linear depth of the sample view Z value
		"		float delta = sampleDepth - realDepth;",

		"		if ( delta > minDistance && delta < maxDistance ) {", // if fragment is before sample point, increase occlusion

		"			occlusion += 1.0;",

		"		}",

		"	}",

		"	occlusion = clamp( occlusion / float( KERNEL_SIZE ), 0.0, 1.0 );",

		"	gl_FragColor = vec4( vec3( 1.0 - occlusion ), 1.0 );",

		"}"

	].join( "\n" )

};

var SSAODepthShader = {

	defines: {
		"PERSPECTIVE_CAMERA": 1
	},

	uniforms: {

		"tDepth": { value: null },
		"cameraNear": { value: null },
		"cameraFar": { value: null },

	},

	vertexShader: [

		"varying vec2 vUv;",

		"void main() {",

		"	vUv = uv;",
		"	gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );",

		"}"

	].join( "\n" ),

	fragmentShader: [

		"uniform sampler2D tDepth;",

		"uniform float cameraNear;",
		"uniform float cameraFar;",

		"varying vec2 vUv;",

		"#include <packing>",

		"float getLinearDepth( const in vec2 screenPosition ) {",

		"	#if PERSPECTIVE_CAMERA == 1",

		"		float fragCoordZ = texture2D( tDepth, screenPosition ).x;",
		"		float viewZ = perspectiveDepthToViewZ( fragCoordZ, cameraNear, cameraFar );",
		"		return viewZToOrthographicDepth( viewZ, cameraNear, cameraFar );",

		"	#else",

		"		return texture2D( depthSampler, coord ).x;",

		"	#endif",

		"}",

		"void main() {",

		"	float depth = getLinearDepth( vUv );",
		"	gl_FragColor = vec4( vec3( 1.0 - depth ), 1.0 );",

		"}"

	].join( "\n" )

};

var SSAOBlurShader = {

	uniforms: {

		"tDiffuse": { value: null },
		"resolution": { value: new Vector2() }

	},

	vertexShader: [

		"varying vec2 vUv;",

		"void main() {",

		"	vUv = uv;",
		"	gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );",

		"}"

	].join( "\n" ),

	fragmentShader: [

		"uniform sampler2D tDiffuse;",

		"uniform vec2 resolution;",

		"varying vec2 vUv;",

		"void main() {",

		"	vec2 texelSize = ( 1.0 / resolution );",
		"	float result = 0.0;",

		"	for ( int i = - 2; i <= 2; i ++ ) {",

		"		for ( int j = - 2; j <= 2; j ++ ) {",

		"			vec2 offset = ( vec2( float( i ), float( j ) ) ) * texelSize;",
		"			result += texture2D( tDiffuse, vUv + offset ).r;",

		"		}",

		"	}",

		"	gl_FragColor = vec4( vec3( result / ( 5.0 * 5.0 ) ), 1.0 );",

		"}"

	].join( "\n" )

};

export { SSAOShader, SSAODepthShader, SSAOBlurShader };