shithub: rgbds

ref: a77b0b396a9e3c5dc96bf88ab79d43e98b8f3e10
dir: /include/gfx/rgba.hpp/

/*
 * This file is part of RGBDS.
 *
 * Copyright (c) 2022, Eldred Habert and RGBDS contributors.
 *
 * SPDX-License-Identifier: MIT
 */

#ifndef RGBDS_GFX_RGBA_HPP
#define RGBDS_GFX_RGBA_HPP

#include <stdint.h>

struct Rgba {
	uint8_t red;
	uint8_t green;
	uint8_t blue;
	uint8_t alpha;

	constexpr Rgba(uint8_t r, uint8_t g, uint8_t b, uint8_t a)
	    : red(r), green(g), blue(b), alpha(a) {}
	/**
	 * Constructs the color from a "packed" RGBA representation (0xRRGGBBAA)
	 */
	explicit constexpr Rgba(uint32_t rgba = 0)
	    : red(rgba >> 24), green(rgba >> 16), blue(rgba >> 8), alpha(rgba) {}

	static constexpr Rgba fromCGBColor(uint16_t cgbColor) {
		constexpr auto _5to8 = [](uint8_t fiveBpp) -> uint8_t {
			fiveBpp &= 0b11111; // For caller's convenience
			return fiveBpp << 3 | fiveBpp >> 2;
		};
		return {_5to8(cgbColor), _5to8(cgbColor >> 5), _5to8(cgbColor >> 10),
		        (uint8_t)(cgbColor & 0x8000 ? 0x00 : 0xFF)};
	}

	/**
	 * Returns this RGBA as a 32-bit number that can be printed in hex (`%08x`) to yield its CSS
	 * representation
	 */
	uint32_t toCSS() const {
		auto shl = [](uint8_t val, unsigned shift) { return static_cast<uint32_t>(val) << shift; };
		return shl(red, 24) | shl(green, 16) | shl(blue, 8) | shl(alpha, 0);
	}
	friend bool operator!=(Rgba const &lhs, Rgba const &rhs) { return lhs.toCSS() != rhs.toCSS(); }

	/**
	 * CGB colors are RGB555, so we use bit 15 to signify that the color is transparent instead
	 * Since the rest of the bits don't matter then, we return 0x8000 exactly.
	 */
	static constexpr uint16_t transparent = 0b1'00000'00000'00000;

	/**
	 * All alpha values strictly below this will be considered transparent
	 */
	static constexpr uint8_t opacity_threshold = 0xF0; // TODO: adjust this
	// TODO: also a transparency threshold, and error out on "middle" values
	bool isTransparent() const { return alpha < opacity_threshold; }
	/**
	 * Computes the equivalent CGB color, respects the color curve depending on options
	 */
	uint16_t cgbColor() const;

	bool isGray() const { return red == green && green == blue; }
	uint8_t grayIndex() const;
};

#endif /* RGBDS_GFX_RGBA_HPP */