HSV and Exposure Composites

Godot 4 shader to change HSV values and exposure.

Instructions

  1. Create a CanvasLayer
  2. Add a ColorRect and sets its anchors to Full Rect
  3. Add a ShaderMaterial and the shader to the ColorRect
Shader code
// Copyright (c) 2024 roland.marchand@protonmail.com
// SPDX short identifier: 0BSD

shader_type canvas_item;

#define F_STOP_SQUARE 1.0
#define MIN_FLOAT 1.17549435e-38
#define MAX_FLOAT 3.402823466e+38
#define EPSILON 0.00001

uniform sampler2D screen_texture: hint_screen_texture, filter_linear, repeat_disable;

uniform float hue: hint_range(-0.5, 0.5, 0.01) = 0.0;
uniform float saturation: hint_range(-1.0, 1.0, 0.01) = 0.0;
uniform float value: hint_range(-1.0, 1.0, 0.01) = 0.0;
// https://upload.wikimedia.org/wikipedia/commons/d/d8/Exposure_program_chart.gif
uniform float exposure: hint_range(0.0, 1.0, 0.01) = 0.5;

bool nearly_equal(float a, float b) {
	float absA = abs(a);
	float absB = abs(b);
	float diff = abs(a - b);

	if (a == b) { // shortcut, handles infinities
		return true;
	} else if (a == 0.0 || b == 0.0 || (absA + absB < MIN_FLOAT)) {
		// a or b is zero or both are extremely close to it
		// relative error is less meaningful here
		return diff < (EPSILON * MIN_FLOAT);
	} else { // use relative error
		return diff / min((absA + absB), MAX_FLOAT) < EPSILON;
	}
}

float get_hue(vec3 rgb) {
	float minimum = min(min(rgb.r, rgb.g), rgb.b);
	float maximum = max(max(rgb.r, rgb.g), rgb.b);
	float delta = maximum - minimum;

	if (nearly_equal(delta, 0.0)) {
		return 0.0;
	}

	float ret;
	if (nearly_equal(rgb.r, maximum)) {
		ret = (rgb.g - rgb.b) / delta; // between yellow & magenta
	} else if (nearly_equal(rgb.g, maximum)) {
		ret = 2.0 + (rgb.b - rgb.r) / delta; // between cyan & yellow
	} else {
		ret = 4.0 + (rgb.r - rgb.g) / delta;// between magenta & cyan
	}

	ret /= 6.0;
	if (ret < 0.0) {
		ret += 1.0;
	}

	return ret;
}

float get_saturation(vec3 rgb) {
	float minimum = min(min(rgb.r, rgb.g), rgb.b);
	float maximum = max(max(rgb.r, rgb.g), rgb.b);
	float delta = maximum - minimum;
	return maximum == 0.0 ? 0.0 : delta / maximum;
}

float get_value(vec3 rgb) {
	return max(max(rgb.r, rgb.g), rgb.b);
}

vec3 get_hsv(vec3 rgb) {
	return vec3(get_hue(rgb), get_saturation(rgb), get_value(rgb));
}

vec3 get_rgb(vec3 hsv) {
	vec3 rgb;
	int i;
	float f, p, q, t;

	if (nearly_equal(hsv.y, 0.0)) {
		rgb.r = rgb.g = rgb.b = hsv.z;
		return rgb;
	}

	hsv.x *= 6.0;
	hsv.x = mod(hsv.x, 6.0);
	i = int(floor(hsv.x));

	f = hsv.x - float(i);
	p = hsv.z * (1.0 - hsv.y);
	q = hsv.z * (1.0 - hsv.y * f);
	t = hsv.z * (1.0 - hsv.y * (1.0 - f));

	switch (i) {
		case 0: // Red is the dominant color
			rgb.r = hsv.z;
			rgb.g = t;
			rgb.b = p;
			break;
		case 1: // Green is the dominant color
			rgb.r = q;
			rgb.g = hsv.z;
			rgb.b = p;
			break;
		case 2:
			rgb.r = p;
			rgb.g = hsv.z;
			rgb.b = t;
			break;
		case 3: // Blue is the dominant color
			rgb.r = p;
			rgb.g = q;
			rgb.b = hsv.z;
			break;
		case 4:
			rgb.r = t;
			rgb.g = p;
			rgb.b = hsv.z;
			break;
		default: // (5) Red is the dominant color
			rgb.r = hsv.z;
			rgb.g = p;
			rgb.b = q;
			break;
	}

	return rgb;
}

void fragment() {
	COLOR = texture(screen_texture, UV);

	vec3 HSV = get_hsv(COLOR.rgb);

	HSV.x = mod(HSV.x + hue, 1.0);
	HSV.y = clamp(HSV.y + saturation, 0.0, 1.0);
	HSV.z = clamp(HSV.z + value, 0.0, 1.0);

	COLOR = vec4(get_rgb(HSV), 1.0);

	// Exposure
	COLOR.rgb *= log2(F_STOP_SQUARE / exposure);
}
Tags
2d, adjustment, Color, exposure, hsv
The shader code and all code snippets in this post are under CC0 license and can be used freely without the author's permission. Images and videos, and assets depicted in those, do not fall under this license. For more info, see our License terms.

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