/**
 * ACES Filmic Tone Mapping Shader by Stephen Hill
 * source: https://github.com/selfshadow/ltc_code/blob/master/webgl/shaders/ltc/ltc_blit.fs
 *
 * this implementation of ACES is modified to accommodate a brighter viewing environment.
 * the scale factor of 1/0.6 is subjective. see discussion in #19621.
 */

const ACESFilmicToneMappingShader = {

	uniforms: {

		'tDiffuse': { value: null },
		'exposure': { value: 1.0 }

	},

	vertexShader: /* glsl */`

		varying vec2 vUv;

		void main() {

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

		}`,

	fragmentShader: /* glsl */`

		#define saturate(a) clamp( a, 0.0, 1.0 )

		uniform sampler2D tDiffuse;

		uniform float exposure;

		varying vec2 vUv;

		vec3 RRTAndODTFit( vec3 v ) {

			vec3 a = v * ( v + 0.0245786 ) - 0.000090537;
			vec3 b = v * ( 0.983729 * v + 0.4329510 ) + 0.238081;
			return a / b;

		}

		vec3 ACESFilmicToneMapping( vec3 color ) {

		// sRGB => XYZ => D65_2_D60 => AP1 => RRT_SAT
			const mat3 ACESInputMat = mat3(
				vec3( 0.59719, 0.07600, 0.02840 ), // transposed from source
				vec3( 0.35458, 0.90834, 0.13383 ),
				vec3( 0.04823, 0.01566, 0.83777 )
			);

		// ODT_SAT => XYZ => D60_2_D65 => sRGB
			const mat3 ACESOutputMat = mat3(
				vec3(  1.60475, -0.10208, -0.00327 ), // transposed from source
				vec3( -0.53108,  1.10813, -0.07276 ),
				vec3( -0.07367, -0.00605,  1.07602 )
			);

			color = ACESInputMat * color;

		// Apply RRT and ODT
			color = RRTAndODTFit( color );

			color = ACESOutputMat * color;

		// Clamp to [0, 1]
			return saturate( color );

		}

		void main() {

			vec4 tex = texture2D( tDiffuse, vUv );

			tex.rgb *= exposure / 0.6; // pre-exposed, outside of the tone mapping function

			gl_FragColor = vec4( ACESFilmicToneMapping( tex.rgb ), tex.a );

		}`

};

export { ACESFilmicToneMappingShader };
