shaderlib: Add multipass pixelsorting

examples/multistep_pixelsort.gdshader

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+shader_type canvas_item;
+
+#include "./shaderlib/pixelsort.gdshaderinc"
+
+//!steps 1500
+uniform int STEP;
+
+//!load ./images/mountain.jpg
+
+void fragment() {
+	// pixel sorting works in multiple steps
+	COLOR = pixelsort_step(
+		TEXTURE, UV,
+		DIRECTION_BOTTOM_TO_TOP,
+		COLOR_MODE_OKLCH,
+		{true, false, false},
+		{-INF, .007, -INF},
+		{INF, INF, INF},
+		STEP);
+}

examples/multistep_pixelsort.gdshader.uid

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+uid://csk0fg4by651b

shaderlib/pixelsort.gdshaderinc

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+
+/*
+	Pixelsorting using odd-even sort
+
+	I roughly followed https://ciphrd.com/2020/04/08/pixel-sorting-on-shader-using-well-crafted-sorting-filters-glsl/
+	- vector fields aren't implemented, diagonal sorting is not supported!
+*/
+
+#include "./hsv.gdshaderinc"
+#include "./oklab.gdshaderinc"
+
+#define INF (1.0/0.0)
+
+#define DIRECTION_LEFT_TO_RIGHT vec2(1, 0)
+#define DIRECTION_RIGHT_TO_LEFT vec2(-1, 0)
+#define DIRECTION_TOP_TO_BOTTOM vec2(0, 1)
+#define DIRECTION_BOTTOM_TO_TOP vec2(0, -1)
+
+#define COLOR_MODE_RGB 0
+#define COLOR_MODE_OKLAB 1
+#define COLOR_MODE_OKLCH 2
+#define COLOR_MODE_HSV 3
+
+vec4 pixelsort_step(
+	sampler2D tex, vec2 uv,
+	vec2 direction, // e.g. (1, 0) for left-to-right or (0, -1) for bottom-to-top
+	                // see DIRECTION_LEFT_TO_RIGHT, etc.
+	                // note: vertical sorting doesn't work, so using e.g. (1, 1) won't work
+	int color_mode, // 0 = RGB, 1 = OKLAB, 2 = OKLCH, 3 = HSV
+	                // see COLOR_MODE_RGB, etc.
+	bool color_channel_mask[3], // which color channel(s) to take into account
+	float lower_threshold[3],   // lower threshold for pixels to be considered sorted
+	                            // when in doubt, use {-INF, -INF, -INF}
+	float upper_threshold[3],   // upper threshold; {INF, INF, INF}
+	int step_ // from STEP
+) {
+	// sanitize inputs
+	direction = clamp(direction, vec2(-1, -1), vec2(1, 1));
+	color_mode = clamp(color_mode, 0, 3);
+	// get neighbour
+	vec2 texture_size = vec2(textureSize(tex, 0));
+	vec2 a = (mod(floor(uv * texture_size), 2.0) * 2.0 - 1.0) * (mod(float(step_), 2.0) * 2.0 - 1.0);
+	vec2 neighbour_uv = uv + (direction * a / texture_size);
+	//
+	vec4 x = texture(tex, uv);
+	vec4 y = texture(tex, neighbour_uv);
+	if ( // stop at borders
+		neighbour_uv.x > 1.0 ||
+		neighbour_uv.x < 0.0 ||
+		neighbour_uv.y > 1.0 ||
+		neighbour_uv.y < 0.0
+	) {
+		return x;
+	} else {
+		// convert color if necessary
+		// get value to compare
+		float vx = 0.0;
+		float vy = 0.0;
+		vec3 color_x;
+		vec3 color_y;
+		if (color_mode == COLOR_MODE_RGB) {
+			color_x = x.rgb;
+			color_y = y.rgb;
+		} else if (color_mode == COLOR_MODE_OKLAB) {
+			color_x = rgb2oklab(x).rgb;
+			color_y = rgb2oklab(y).rgb;
+		} else if (color_mode == COLOR_MODE_OKLCH) {
+			color_x = oklab2oklch(rgb2oklab(x)).rgb;
+			color_y = oklab2oklch(rgb2oklab(y)).rgb;
+		} else if (color_mode == COLOR_MODE_HSV) {
+			color_x = rgb2hsv(x).rgb;
+			color_y = rgb2hsv(y).rgb;
+		}
+		float divisor = 0.0;
+		if (color_channel_mask[0]) {
+			vx += color_x.r;
+			vy += color_y.r;
+			divisor += 1.0;
+		}
+		if (color_channel_mask[1]) {
+			vx += color_x.g;
+			vy += color_y.g;
+			divisor += 1.0;
+		}
+		if (color_channel_mask[2]) {
+			vx += color_x.b;
+			vy += color_y.b;
+			divisor += 1.0;
+		}
+		divisor = max(divisor, 1.0);
+		vx /= divisor;
+		vy /= divisor;
+		//
+		if (
+			(a.x < .0 && abs(direction).y == .0) ||
+			(a.y < .0 && abs(direction).x == .0)
+		) {
+			if (
+				vy > vx &&
+				// threshold
+				color_x.r < upper_threshold[0] &&
+				color_x.g < upper_threshold[1] &&
+				color_x.b < upper_threshold[2] &&
+				color_x.r > lower_threshold[0] &&
+				color_x.g > lower_threshold[1] &&
+				color_x.b > lower_threshold[2]
+			) { return y; }
+			else { return x; }
+		} else if (
+			(a.x > .0 && abs(direction).y == .0) ||
+			(a.y > .0 && abs(direction).x == .0)
+		) {
+			if (
+				vx >= vy &&
+				// threshold
+				color_y.r < upper_threshold[0] &&
+				color_y.g < upper_threshold[1] &&
+				color_y.b < upper_threshold[2] &&
+				color_y.r > lower_threshold[0] &&
+				color_y.g > lower_threshold[1] &&
+				color_y.b > lower_threshold[2]
+			) { return y; }
+			else { return x; }
+		}
+	}
+}

shaderlib/pixelsort.gdshaderinc.uid

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+uid://doefnwk3vyr0o