// 4xBRZ shader - Copyright (C) 2014-2016 DeSmuME team (GPL2+)
// Hyllians xBR-vertex code and texel mapping
// Copyright (C) 2011/2016 Hyllian - sergiogdb@gmail.com
#define BLEND_ALPHA 1
#define BLEND_NONE 0
#define BLEND_NORMAL 1
#define BLEND_DOMINANT 2
#define LUMINANCE_WEIGHT 1.0
#define EQUAL_COLOR_TOLERANCE 30.0/255.0
#define STEEP_DIRECTION_THRESHOLD 2.2
#define DOMINANT_DIRECTION_THRESHOLD 3.6

// TODO: Replace this with something cheaper.
float DistYCbCr(vec4 pixA, vec4 pixB) {
	// https://en.wikipedia.org/wiki/YCbCr#ITU-R_BT.2020_conversion
	const vec3 K = vec3(0.2627, 0.6780, 0.0593);
	const mat3 MATRIX = mat3(K,
		-.5 * K.r / (1.0 - K.b), -.5 * K.g / (1.0 - K.b), .5,
		.5, -.5 * K.g / (1.0 - K.r), -.5 * K.b / (1.0 - K.r));
	vec4 diff = pixA - pixB;
	vec3 YCbCr = diff.rgb * MATRIX;
	YCbCr.x *= LUMINANCE_WEIGHT;
	float d = dot(YCbCr, YCbCr);
	return sqrt(pixA.a * pixB.a * d + diff.a * diff.a);
}

bool IsPixEqual(const vec4 pixA, const vec4 pixB) {
	return (DistYCbCr(pixA, pixB) < EQUAL_COLOR_TOLERANCE);
}

bool IsBlendingNeeded(const ivec4 blend) {
	ivec4 diff = blend - ivec4(BLEND_NONE);
	return diff.x != 0 || diff.y != 0 || diff.z != 0 || diff.w != 0;
}

uint readInputu(uvec2 coord) {
	return readColoru(uvec2(clamp(coord.x, 0, params.width - 1), clamp(coord.y, 0, params.height - 1)));
}

vec4 readInput(uvec2 coord) {
	return readColorf(uvec2(clamp(coord.x, 0, params.width - 1), clamp(coord.y, 0, params.height - 1)));
}

void applyScaling(uvec2 origxy) {
	//    A1 B1 C1
	// A0 A  B  C C4
	// D0 D  E  F F4
	// G0 G  H  I I4
	//    G5 H5 I5

	uvec4 t1 = uvec4(origxy.x - 1, origxy.x, origxy.x + 1, origxy.y - 2); // A1 B1 C1
	uvec4 t2 = uvec4(origxy.x - 1, origxy.x, origxy.x + 1, origxy.y - 1); // A B C
	uvec4 t3 = uvec4(origxy.x - 1, origxy.x, origxy.x + 1, origxy.y + 0); // D E F
	uvec4 t4 = uvec4(origxy.x - 1, origxy.x, origxy.x + 1, origxy.y + 1); // G H I
	uvec4 t5 = uvec4(origxy.x - 1, origxy.x, origxy.x + 1, origxy.y + 2); // G5 H5 I5
	uvec4 t6 = uvec4(origxy.x - 2, origxy.y - 1, origxy.y, origxy.y + 1); // A0 D0 G0
	uvec4 t7 = uvec4(origxy.x + 2, origxy.y - 1, origxy.y, origxy.y + 1); // C4 F4 I4

	//---------------------------------------
	// Input Pixel Mapping:    |21|22|23|
	//                       19|06|07|08|09
	//                       18|05|00|01|10
	//                       17|04|03|02|11
	//                         |15|14|13|

	uint v[9];
	v[0] = readInputu(t3.yw);
	v[1] = readInputu(t3.zw);
	v[2] = readInputu(t4.zw);
	v[3] = readInputu(t4.yw);
	v[4] = readInputu(t4.xw);
	v[5] = readInputu(t3.xw);
	v[6] = readInputu(t2.xw);
	v[7] = readInputu(t2.yw);
	v[8] = readInputu(t2.zw);

	vec4 src[25];

	src[21] = readInput(t1.xw);
	src[22] = readInput(t1.yw);
	src[23] = readInput(t1.zw);
	src[ 6] = unpackUnorm4x8(v[6]);
	src[ 7] = unpackUnorm4x8(v[7]);
	src[ 8] = unpackUnorm4x8(v[8]);
	src[ 5] = unpackUnorm4x8(v[5]);
	src[ 0] = unpackUnorm4x8(v[0]);
	src[ 1] = unpackUnorm4x8(v[1]);
	src[ 4] = unpackUnorm4x8(v[4]);
	src[ 3] = unpackUnorm4x8(v[3]);
	src[ 2] = unpackUnorm4x8(v[2]);
	src[15] = readInput(t5.xw);
	src[14] = readInput(t5.yw);
	src[13] = readInput(t5.zw);
	src[19] = readInput(t6.xy);
	src[18] = readInput(t6.xz);
	src[17] = readInput(t6.xw);
	src[ 9] = readInput(t7.xy);
	src[10] = readInput(t7.xz);
	src[11] = readInput(t7.xw);

	ivec4 blendResult = ivec4(BLEND_NONE);

	// Preserve old alpha-ignoring behavior? Keep or delete?
	for (int i = 0; i < 9; i++) {
		v[i] &= 0xFFFFFF;
	}

	// Preprocess corners
	// Pixel Tap Mapping: --|--|--|--|--
	//                    --|--|07|08|--
	//                    --|05|00|01|10
	//                    --|04|03|02|11
	//                    --|--|14|13|--
	// Corner (1, 1)
	if ( ((v[0] == v[1] && v[3] == v[2]) || (v[0] == v[3] && v[1] == v[2])) == false) {
		float dist_03_01 = DistYCbCr(src[ 4], src[ 0]) + DistYCbCr(src[ 0], src[ 8]) + DistYCbCr(src[14], src[ 2]) + DistYCbCr(src[ 2], src[10]) + (4.0 * DistYCbCr(src[ 3], src[ 1]));
		float dist_00_02 = DistYCbCr(src[ 5], src[ 3]) + DistYCbCr(src[ 3], src[13]) + DistYCbCr(src[ 7], src[ 1]) + DistYCbCr(src[ 1], src[11]) + (4.0 * DistYCbCr(src[ 0], src[ 2]));
		bool dominantGradient = (DOMINANT_DIRECTION_THRESHOLD * dist_03_01) < dist_00_02;
		blendResult[2] = ((dist_03_01 < dist_00_02) && (v[0] != v[1]) && (v[0] != v[3])) ? ((dominantGradient) ? BLEND_DOMINANT : BLEND_NORMAL) : BLEND_NONE;
	}

	// Pixel Tap Mapping: --|--|--|--|--
	//                    --|06|07|--|--
	//                    18|05|00|01|--
	//                    17|04|03|02|--
	//                    --|15|14|--|--
	// Corner (0, 1)
	if ( ((v[5] == v[0] && v[4] == v[3]) || (v[5] == v[4] && v[0] == v[3])) == false) {
		float dist_04_00 = DistYCbCr(src[17], src[ 5]) + DistYCbCr(src[ 5], src[ 7]) + DistYCbCr(src[15], src[ 3]) + DistYCbCr(src[ 3], src[ 1]) + (4.0 * DistYCbCr(src[ 4], src[ 0]));
		float dist_05_03 = DistYCbCr(src[18], src[ 4]) + DistYCbCr(src[ 4], src[14]) + DistYCbCr(src[ 6], src[ 0]) + DistYCbCr(src[ 0], src[ 2]) + (4.0 * DistYCbCr(src[ 5], src[ 3]));
		bool dominantGradient = (DOMINANT_DIRECTION_THRESHOLD * dist_05_03) < dist_04_00;
		blendResult[3] = ((dist_04_00 > dist_05_03) && (v[0] != v[5]) && (v[0] != v[3])) ? ((dominantGradient) ? BLEND_DOMINANT : BLEND_NORMAL) : BLEND_NONE;
	}

	// Pixel Tap Mapping: --|--|22|23|--
	//                    --|06|07|08|09
	//                    --|05|00|01|10
	//                    --|--|03|02|--
	//                    --|--|--|--|--
	// Corner (1, 0)
	if ( ((v[7] == v[8] && v[0] == v[1]) || (v[7] == v[0] && v[8] == v[1])) == false) {
		float dist_00_08 = DistYCbCr(src[ 5], src[ 7]) + DistYCbCr(src[ 7], src[23]) + DistYCbCr(src[ 3], src[ 1]) + DistYCbCr(src[ 1], src[ 9]) + (4.0 * DistYCbCr(src[ 0], src[ 8]));
		float dist_07_01 = DistYCbCr(src[ 6], src[ 0]) + DistYCbCr(src[ 0], src[ 2]) + DistYCbCr(src[22], src[ 8]) + DistYCbCr(src[ 8], src[10]) + (4.0 * DistYCbCr(src[ 7], src[ 1]));
		bool dominantGradient = (DOMINANT_DIRECTION_THRESHOLD * dist_07_01) < dist_00_08;
		blendResult[1] = ((dist_00_08 > dist_07_01) && (v[0] != v[7]) && (v[0] != v[1])) ? ((dominantGradient) ? BLEND_DOMINANT : BLEND_NORMAL) : BLEND_NONE;
	}

	// Pixel Tap Mapping: --|21|22|--|--
	//                    19|06|07|08|--
	//                    18|05|00|01|--
	//                    --|04|03|--|--
	//                    --|--|--|--|--
	// Corner (0, 0)
	if ( ((v[6] == v[7] && v[5] == v[0]) || (v[6] == v[5] && v[7] == v[0])) == false) {
		float dist_05_07 = DistYCbCr(src[18], src[ 6]) + DistYCbCr(src[ 6], src[22]) + DistYCbCr(src[ 4], src[ 0]) + DistYCbCr(src[ 0], src[ 8]) + (4.0 * DistYCbCr(src[ 5], src[ 7]));
		float dist_06_00 = DistYCbCr(src[19], src[ 5]) + DistYCbCr(src[ 5], src[ 3]) + DistYCbCr(src[21], src[ 7]) + DistYCbCr(src[ 7], src[ 1]) + (4.0 * DistYCbCr(src[ 6], src[ 0]));
		bool dominantGradient = (DOMINANT_DIRECTION_THRESHOLD * dist_05_07) < dist_06_00;
		blendResult[0] = ((dist_05_07 < dist_06_00) && (v[0] != v[5]) && (v[0] != v[7])) ? ((dominantGradient) ? BLEND_DOMINANT : BLEND_NORMAL) : BLEND_NONE;
	}

	vec4 dst[16];
	dst[ 0] = src[0];
	dst[ 1] = src[0];
	dst[ 2] = src[0];
	dst[ 3] = src[0];
	dst[ 4] = src[0];
	dst[ 5] = src[0];
	dst[ 6] = src[0];
	dst[ 7] = src[0];
	dst[ 8] = src[0];
	dst[ 9] = src[0];
	dst[10] = src[0];
	dst[11] = src[0];
	dst[12] = src[0];
	dst[13] = src[0];
	dst[14] = src[0];
	dst[15] = src[0];

	// Scale pixel
	if (IsBlendingNeeded(blendResult) == true) {
		float dist_01_04 = DistYCbCr(src[1], src[4]);
		float dist_03_08 = DistYCbCr(src[3], src[8]);
		bool haveShallowLine = (STEEP_DIRECTION_THRESHOLD * dist_01_04 <= dist_03_08) && (v[0] != v[4]) && (v[5] != v[4]);
		bool haveSteepLine   = (STEEP_DIRECTION_THRESHOLD * dist_03_08 <= dist_01_04) && (v[0] != v[8]) && (v[7] != v[8]);
		bool needBlend = (blendResult[2] != BLEND_NONE);
		bool doLineBlend = (  blendResult[2] >= BLEND_DOMINANT ||
			((blendResult[1] != BLEND_NONE && !IsPixEqual(src[0], src[4])) ||
			(blendResult[3] != BLEND_NONE && !IsPixEqual(src[0], src[8])) ||
			(IsPixEqual(src[4], src[3]) && IsPixEqual(src[3], src[2]) && IsPixEqual(src[2], src[1]) && IsPixEqual(src[1], src[8]) && IsPixEqual(src[0], src[2]) == false) ) == false );

		vec4 blendPix = ( DistYCbCr(src[0], src[1]) <= DistYCbCr(src[0], src[3]) ) ? src[1] : src[3];
		dst[ 2] = mix(dst[ 2], blendPix, (needBlend && doLineBlend) ? ((haveShallowLine) ? ((haveSteepLine) ? 1.0/3.0 : 0.25) : ((haveSteepLine) ? 0.25 : 0.00)) : 0.00);
		dst[ 9] = mix(dst[ 9], blendPix, (needBlend && doLineBlend && haveSteepLine) ? 0.25 : 0.00);
		dst[10] = mix(dst[10], blendPix, (needBlend && doLineBlend && haveSteepLine) ? 0.75 : 0.00);
		dst[11] = mix(dst[11], blendPix, (needBlend) ? ((doLineBlend) ? ((haveSteepLine) ? 1.00 : ((haveShallowLine) ? 0.75 : 0.50)) : 0.08677704501) : 0.00);
		dst[12] = mix(dst[12], blendPix, (needBlend) ? ((doLineBlend) ? 1.00 : 0.6848532563) : 0.00);
		dst[13] = mix(dst[13], blendPix, (needBlend) ? ((doLineBlend) ? ((haveShallowLine) ? 1.00 : ((haveSteepLine) ? 0.75 : 0.50)) : 0.08677704501) : 0.00);
		dst[14] = mix(dst[14], blendPix, (needBlend && doLineBlend && haveShallowLine) ? 0.75 : 0.00);
		dst[15] = mix(dst[15], blendPix, (needBlend && doLineBlend && haveShallowLine) ? 0.25 : 0.00);

		dist_01_04 = DistYCbCr(src[7], src[2]);
		dist_03_08 = DistYCbCr(src[1], src[6]);
		haveShallowLine = (STEEP_DIRECTION_THRESHOLD * dist_01_04 <= dist_03_08) && (v[0] != v[2]) && (v[3] != v[2]);
		haveSteepLine   = (STEEP_DIRECTION_THRESHOLD * dist_03_08 <= dist_01_04) && (v[0] != v[6]) && (v[5] != v[6]);
		needBlend = (blendResult[1] != BLEND_NONE);
		doLineBlend = (  blendResult[1] >= BLEND_DOMINANT ||
			!((blendResult[0] != BLEND_NONE && !IsPixEqual(src[0], src[2])) ||
			(blendResult[2] != BLEND_NONE && !IsPixEqual(src[0], src[6])) ||
			(IsPixEqual(src[2], src[1]) && IsPixEqual(src[1], src[8]) && IsPixEqual(src[8], src[7]) && IsPixEqual(src[7], src[6]) && !IsPixEqual(src[0], src[8])) ) );

		blendPix = ( DistYCbCr(src[0], src[7]) <= DistYCbCr(src[0], src[1]) ) ? src[7] : src[1];
		dst[ 1] = mix(dst[ 1], blendPix, (needBlend && doLineBlend) ? ((haveShallowLine) ? ((haveSteepLine) ? 1.0/3.0 : 0.25) : ((haveSteepLine) ? 0.25 : 0.00)) : 0.00);
		dst[ 6] = mix(dst[ 6], blendPix, (needBlend && doLineBlend && haveSteepLine) ? 0.25 : 0.00);
		dst[ 7] = mix(dst[ 7], blendPix, (needBlend && doLineBlend && haveSteepLine) ? 0.75 : 0.00);
		dst[ 8] = mix(dst[ 8], blendPix, (needBlend) ? ((doLineBlend) ? ((haveSteepLine) ? 1.00 : ((haveShallowLine) ? 0.75 : 0.50)) : 0.08677704501) : 0.00);
		dst[ 9] = mix(dst[ 9], blendPix, (needBlend) ? ((doLineBlend) ? 1.00 : 0.6848532563) : 0.00);
		dst[10] = mix(dst[10], blendPix, (needBlend) ? ((doLineBlend) ? ((haveShallowLine) ? 1.00 : ((haveSteepLine) ? 0.75 : 0.50)) : 0.08677704501) : 0.00);
		dst[11] = mix(dst[11], blendPix, (needBlend && doLineBlend && haveShallowLine) ? 0.75 : 0.00);
		dst[12] = mix(dst[12], blendPix, (needBlend && doLineBlend && haveShallowLine) ? 0.25 : 0.00);

		dist_01_04 = DistYCbCr(src[5], src[8]);
		dist_03_08 = DistYCbCr(src[7], src[4]);
		haveShallowLine = (STEEP_DIRECTION_THRESHOLD * dist_01_04 <= dist_03_08) && (v[0] != v[8]) && (v[1] != v[8]);
		haveSteepLine   = (STEEP_DIRECTION_THRESHOLD * dist_03_08 <= dist_01_04) && (v[0] != v[4]) && (v[3] != v[4]);
		needBlend = (blendResult[0] != BLEND_NONE);
		doLineBlend = (  blendResult[0] >= BLEND_DOMINANT ||
			!((blendResult[3] != BLEND_NONE && !IsPixEqual(src[0], src[8])) ||
			(blendResult[1] != BLEND_NONE && !IsPixEqual(src[0], src[4])) ||
			(IsPixEqual(src[8], src[7]) && IsPixEqual(src[7], src[6]) && IsPixEqual(src[6], src[5]) && IsPixEqual(src[5], src[4]) && !IsPixEqual(src[0], src[6])) ) );

		blendPix = ( DistYCbCr(src[0], src[5]) <= DistYCbCr(src[0], src[7]) ) ? src[5] : src[7];
		dst[ 0] = mix(dst[ 0], blendPix, (needBlend && doLineBlend) ? ((haveShallowLine) ? ((haveSteepLine) ? 1.0/3.0 : 0.25) : ((haveSteepLine) ? 0.25 : 0.00)) : 0.00);
		dst[15] = mix(dst[15], blendPix, (needBlend && doLineBlend && haveSteepLine) ? 0.25 : 0.00);
		dst[ 4] = mix(dst[ 4], blendPix, (needBlend && doLineBlend && haveSteepLine) ? 0.75 : 0.00);
		dst[ 5] = mix(dst[ 5], blendPix, (needBlend) ? ((doLineBlend) ? ((haveSteepLine) ? 1.00 : ((haveShallowLine) ? 0.75 : 0.50)) : 0.08677704501) : 0.00);
		dst[ 6] = mix(dst[ 6], blendPix, (needBlend) ? ((doLineBlend) ? 1.00 : 0.6848532563) : 0.00);
		dst[ 7] = mix(dst[ 7], blendPix, (needBlend) ? ((doLineBlend) ? ((haveShallowLine) ? 1.00 : ((haveSteepLine) ? 0.75 : 0.50)) : 0.08677704501) : 0.00);
		dst[ 8] = mix(dst[ 8], blendPix, (needBlend && doLineBlend && haveShallowLine) ? 0.75 : 0.00);
		dst[ 9] = mix(dst[ 9], blendPix, (needBlend && doLineBlend && haveShallowLine) ? 0.25 : 0.00);

		dist_01_04 = DistYCbCr(src[3], src[6]);
		dist_03_08 = DistYCbCr(src[5], src[2]);
		haveShallowLine = (STEEP_DIRECTION_THRESHOLD * dist_01_04 <= dist_03_08) && (v[0] != v[6]) && (v[7] != v[6]);
		haveSteepLine   = (STEEP_DIRECTION_THRESHOLD * dist_03_08 <= dist_01_04) && (v[0] != v[2]) && (v[1] != v[2]);
		needBlend = (blendResult[3] != BLEND_NONE);
		doLineBlend = (  blendResult[3] >= BLEND_DOMINANT ||
			!((blendResult[2] != BLEND_NONE && !IsPixEqual(src[0], src[6])) ||
			(blendResult[0] != BLEND_NONE && !IsPixEqual(src[0], src[2])) ||
			(IsPixEqual(src[6], src[5]) && IsPixEqual(src[5], src[4]) && IsPixEqual(src[4], src[3]) && IsPixEqual(src[3], src[2]) && !IsPixEqual(src[0], src[4])) ) );

		blendPix = ( DistYCbCr(src[0], src[3]) <= DistYCbCr(src[0], src[5]) ) ? src[3] : src[5];
		dst[ 3] = mix(dst[ 3], blendPix, (needBlend && doLineBlend) ? ((haveShallowLine) ? ((haveSteepLine) ? 1.0/3.0 : 0.25) : ((haveSteepLine) ? 0.25 : 0.00)) : 0.00);
		dst[12] = mix(dst[12], blendPix, (needBlend && doLineBlend && haveSteepLine) ? 0.25 : 0.00);
		dst[13] = mix(dst[13], blendPix, (needBlend && doLineBlend && haveSteepLine) ? 0.75 : 0.00);
		dst[14] = mix(dst[14], blendPix, (needBlend) ? ((doLineBlend) ? ((haveSteepLine) ? 1.00 : ((haveShallowLine) ? 0.75 : 0.50)) : 0.08677704501) : 0.00);
		dst[15] = mix(dst[15], blendPix, (needBlend) ? ((doLineBlend) ? 1.00 : 0.6848532563) : 0.00);
		dst[ 4] = mix(dst[ 4], blendPix, (needBlend) ? ((doLineBlend) ? ((haveShallowLine) ? 1.00 : ((haveSteepLine) ? 0.75 : 0.50)) : 0.08677704501) : 0.00);
		dst[ 5] = mix(dst[ 5], blendPix, (needBlend && doLineBlend && haveShallowLine) ? 0.75 : 0.00);
		dst[ 6] = mix(dst[ 6], blendPix, (needBlend && doLineBlend && haveShallowLine) ? 0.25 : 0.00);
	}

	// This is the only difference from tex_4xbrz.csh:

	// Output Pixel Mapping:
	//   06|07|08|09
	//   05|00|01|10
	//   04|03|02|11
	//   15|14|13|12
	// Write all 16 output pixels.
	ivec2 destXY = ivec2(origxy) * 2;

	vec4 topLeft = dst[6] + dst[7] + dst[5] + dst[0];
	vec4 topRight = dst[8] + dst[9] + dst[1] + dst[10];
	vec4 bottomLeft = dst[4] + dst[3] + dst[15] + dst[14];
	vec4 bottomRight = dst[2] + dst[11] + dst[13] + dst[12];
	writeColorf(destXY, topLeft * 0.25);
	writeColorf(destXY + ivec2(1, 0), topRight * 0.25);
	writeColorf(destXY + ivec2(0, 1), bottomLeft * 0.25);
	writeColorf(destXY + ivec2(1, 1), bottomRight * 0.25);
}
