/**
 * @author mikael emtinger / http://gomo.se/
 * @author alteredq / http://alteredqualia.com/
 */

THREE.SpritePlugin = function ( ) {

	var _gl, _renderer, _sprite = {};

	this.init = function ( renderer ) {

		_gl = renderer.context;
		_renderer = renderer;

		_sprite.vertices = new Float32Array( 8 + 8 );
		_sprite.faces    = new Uint16Array( 6 );

		var i = 0;

		_sprite.vertices[ i++ ] = -1; _sprite.vertices[ i++ ] = -1;	// vertex 0
		_sprite.vertices[ i++ ] = 0;  _sprite.vertices[ i++ ] = 0;	// uv 0

		_sprite.vertices[ i++ ] = 1;  _sprite.vertices[ i++ ] = -1;	// vertex 1
		_sprite.vertices[ i++ ] = 1;  _sprite.vertices[ i++ ] = 0;	// uv 1

		_sprite.vertices[ i++ ] = 1;  _sprite.vertices[ i++ ] = 1;	// vertex 2
		_sprite.vertices[ i++ ] = 1;  _sprite.vertices[ i++ ] = 1;	// uv 2

		_sprite.vertices[ i++ ] = -1; _sprite.vertices[ i++ ] = 1;	// vertex 3
		_sprite.vertices[ i++ ] = 0;  _sprite.vertices[ i++ ] = 1;	// uv 3

		i = 0;

		_sprite.faces[ i++ ] = 0; _sprite.faces[ i++ ] = 1; _sprite.faces[ i++ ] = 2;
		_sprite.faces[ i++ ] = 0; _sprite.faces[ i++ ] = 2; _sprite.faces[ i++ ] = 3;

		_sprite.vertexBuffer  = _gl.createBuffer();
		_sprite.elementBuffer = _gl.createBuffer();

		_gl.bindBuffer( _gl.ARRAY_BUFFER, _sprite.vertexBuffer );
		_gl.bufferData( _gl.ARRAY_BUFFER, _sprite.vertices, _gl.STATIC_DRAW );

		_gl.bindBuffer( _gl.ELEMENT_ARRAY_BUFFER, _sprite.elementBuffer );
		_gl.bufferData( _gl.ELEMENT_ARRAY_BUFFER, _sprite.faces, _gl.STATIC_DRAW );

		_sprite.program = createProgram( THREE.ShaderSprite[ "sprite" ] );

		_sprite.attributes = {};
		_sprite.uniforms = {};

		_sprite.attributes.position           = _gl.getAttribLocation ( _sprite.program, "position" );
		_sprite.attributes.uv                 = _gl.getAttribLocation ( _sprite.program, "uv" );

		_sprite.uniforms.uvOffset             = _gl.getUniformLocation( _sprite.program, "uvOffset" );
		_sprite.uniforms.uvScale              = _gl.getUniformLocation( _sprite.program, "uvScale" );

		_sprite.uniforms.rotation             = _gl.getUniformLocation( _sprite.program, "rotation" );
		_sprite.uniforms.scale                = _gl.getUniformLocation( _sprite.program, "scale" );
		_sprite.uniforms.alignment            = _gl.getUniformLocation( _sprite.program, "alignment" );

		_sprite.uniforms.color                = _gl.getUniformLocation( _sprite.program, "color" );
		_sprite.uniforms.map                  = _gl.getUniformLocation( _sprite.program, "map" );
		_sprite.uniforms.opacity              = _gl.getUniformLocation( _sprite.program, "opacity" );

		_sprite.uniforms.useScreenCoordinates = _gl.getUniformLocation( _sprite.program, "useScreenCoordinates" );
		_sprite.uniforms.sizeAttenuation   	  = _gl.getUniformLocation( _sprite.program, "sizeAttenuation" );
		_sprite.uniforms.screenPosition    	  = _gl.getUniformLocation( _sprite.program, "screenPosition" );
		_sprite.uniforms.modelViewMatrix      = _gl.getUniformLocation( _sprite.program, "modelViewMatrix" );
		_sprite.uniforms.projectionMatrix     = _gl.getUniformLocation( _sprite.program, "projectionMatrix" );

		_sprite.uniforms.fogType 		  	  = _gl.getUniformLocation( _sprite.program, "fogType" );
		_sprite.uniforms.fogDensity 		  = _gl.getUniformLocation( _sprite.program, "fogDensity" );
		_sprite.uniforms.fogNear 		  	  = _gl.getUniformLocation( _sprite.program, "fogNear" );
		_sprite.uniforms.fogFar 		  	  = _gl.getUniformLocation( _sprite.program, "fogFar" );
		_sprite.uniforms.fogColor 		  	  = _gl.getUniformLocation( _sprite.program, "fogColor" );

		_sprite.uniforms.alphaTest 		  	  = _gl.getUniformLocation( _sprite.program, "alphaTest" );

	};

	this.render = function ( scene, camera, viewportWidth, viewportHeight ) {

		var sprites = scene.__webglSprites,
			nSprites = sprites.length;

		if ( ! nSprites ) return;

		var attributes = _sprite.attributes,
			uniforms = _sprite.uniforms;

		var invAspect = viewportHeight / viewportWidth;

		var halfViewportWidth = viewportWidth * 0.5,
			halfViewportHeight = viewportHeight * 0.5;

		// setup gl

		_gl.useProgram( _sprite.program );

		_gl.enableVertexAttribArray( attributes.position );
		_gl.enableVertexAttribArray( attributes.uv );

		_gl.disable( _gl.CULL_FACE );
		_gl.enable( _gl.BLEND );

		_gl.bindBuffer( _gl.ARRAY_BUFFER, _sprite.vertexBuffer );
		_gl.vertexAttribPointer( attributes.position, 2, _gl.FLOAT, false, 2 * 8, 0 );
		_gl.vertexAttribPointer( attributes.uv, 2, _gl.FLOAT, false, 2 * 8, 8 );

		_gl.bindBuffer( _gl.ELEMENT_ARRAY_BUFFER, _sprite.elementBuffer );

		_gl.uniformMatrix4fv( uniforms.projectionMatrix, false, camera.projectionMatrix.elements );

		_gl.activeTexture( _gl.TEXTURE0 );
		_gl.uniform1i( uniforms.map, 0 );

		var oldFogType = 0;
		var sceneFogType = 0;
		var fog = scene.fog;

		if ( fog ) {

			_gl.uniform3f( uniforms.fogColor, fog.color.r, fog.color.g, fog.color.b );

			if ( fog instanceof THREE.Fog ) {

				_gl.uniform1f( uniforms.fogNear, fog.near );
				_gl.uniform1f( uniforms.fogFar, fog.far );

				_gl.uniform1i( uniforms.fogType, 1 );
				oldFogType = 1;
				sceneFogType = 1;

			} else if ( fog instanceof THREE.FogExp2 ) {

				_gl.uniform1f( uniforms.fogDensity, fog.density );

				_gl.uniform1i( uniforms.fogType, 2 );
				oldFogType = 2;
				sceneFogType = 2;

			}

		} else {

			_gl.uniform1i( uniforms.fogType, 0 );
			oldFogType = 0;
			sceneFogType = 0;

		}


		// update positions and sort

		var i, sprite, material, screenPosition, size, fogType, scale = [];

		for( i = 0; i < nSprites; i ++ ) {

			sprite = sprites[ i ];
			material = sprite.material;

			if ( ! sprite.visible || material.opacity === 0 ) continue;

			if ( ! material.useScreenCoordinates ) {

				sprite._modelViewMatrix.multiply( camera.matrixWorldInverse, sprite.matrixWorld );
				sprite.z = - sprite._modelViewMatrix.elements[ 14 ];

			} else {

				sprite.z = - sprite.position.z;

			}

		}

		sprites.sort( painterSortStable );

		// render all sprites

		for( i = 0; i < nSprites; i ++ ) {

			sprite = sprites[ i ];
			material = sprite.material;

			if ( ! sprite.visible || material.opacity === 0 ) continue;

			if ( material.map && material.map.image && material.map.image.width ) {

				_gl.uniform1f( uniforms.alphaTest, material.alphaTest );

				if ( material.useScreenCoordinates === true ) {

					_gl.uniform1i( uniforms.useScreenCoordinates, 1 );
					_gl.uniform3f(
						uniforms.screenPosition,
						( ( sprite.position.x * _renderer.devicePixelRatio ) - halfViewportWidth  ) / halfViewportWidth,
						( halfViewportHeight - ( sprite.position.y * _renderer.devicePixelRatio ) ) / halfViewportHeight,
						Math.max( 0, Math.min( 1, sprite.position.z ) )
					);

					scale[ 0 ] = _renderer.devicePixelRatio;
					scale[ 1 ] = _renderer.devicePixelRatio;

				} else {

					_gl.uniform1i( uniforms.useScreenCoordinates, 0 );
					_gl.uniform1i( uniforms.sizeAttenuation, material.sizeAttenuation ? 1 : 0 );
					_gl.uniformMatrix4fv( uniforms.modelViewMatrix, false, sprite._modelViewMatrix.elements );

					scale[ 0 ] = 1;
					scale[ 1 ] = 1;

				}

				if ( scene.fog && material.fog ) {

					fogType = sceneFogType;

				} else {

					fogType = 0;

				}

				if ( oldFogType !== fogType ) {

					_gl.uniform1i( uniforms.fogType, fogType );
					oldFogType = fogType;

				}

				size = 1 / ( material.scaleByViewport ? viewportHeight : 1 );

				scale[ 0 ] *= size * invAspect * sprite.scale.x
				scale[ 1 ] *= size * sprite.scale.y;

				_gl.uniform2f( uniforms.uvScale, material.uvScale.x, material.uvScale.y );
				_gl.uniform2f( uniforms.uvOffset, material.uvOffset.x, material.uvOffset.y );
				_gl.uniform2f( uniforms.alignment, material.alignment.x, material.alignment.y );

				_gl.uniform1f( uniforms.opacity, material.opacity );
				_gl.uniform3f( uniforms.color, material.color.r, material.color.g, material.color.b );

				_gl.uniform1f( uniforms.rotation, sprite.rotation );
				_gl.uniform2fv( uniforms.scale, scale );

				_renderer.setBlending( material.blending, material.blendEquation, material.blendSrc, material.blendDst );
				_renderer.setDepthTest( material.depthTest );
				_renderer.setDepthWrite( material.depthWrite );
				_renderer.setTexture( material.map, 0 );

				_gl.drawElements( _gl.TRIANGLES, 6, _gl.UNSIGNED_SHORT, 0 );

			}

		}

		// restore gl

		_gl.enable( _gl.CULL_FACE );

	};

	function createProgram ( shader ) {

		var program = _gl.createProgram();

		var fragmentShader = _gl.createShader( _gl.FRAGMENT_SHADER );
		var vertexShader = _gl.createShader( _gl.VERTEX_SHADER );

		_gl.shaderSource( fragmentShader, shader.fragmentShader );
		_gl.shaderSource( vertexShader, shader.vertexShader );

		_gl.compileShader( fragmentShader );
		_gl.compileShader( vertexShader );

		_gl.attachShader( program, fragmentShader );
		_gl.attachShader( program, vertexShader );

		_gl.linkProgram( program );

		return program;

	};

	function painterSortStable ( a, b ) {

		if ( a.z !== b.z ) {

			return b.z - a.z;

		} else {

			return b.id - a.id;

		}

	};

};