From b6fd6630dcdabc2dee4d5754a4470cd4b2934c2e Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Sat, 28 May 2022 18:54:17 +0300
Subject: [PATCH] Add color (un)premultiplication utils

---
 libs/gfx/include/psemek/gfx/color.hpp | 59 +++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/libs/gfx/include/psemek/gfx/color.hpp b/libs/gfx/include/psemek/gfx/color.hpp
index 497267bb..8f66532a 100644
--- a/libs/gfx/include/psemek/gfx/color.hpp
+++ b/libs/gfx/include/psemek/gfx/color.hpp
@@ -104,6 +104,65 @@ namespace psemek::gfx
 		return to_srgb(c, 1.f / g);
 	}
 
+	inline geom::vector<float, 4> premult(geom::vector<float, 4> const & c)
+	{
+		return {c[0] * c[3], c[1] * c[3], c[2] * c[3], c[3]};
+	}
+
+	inline geom::vector<std::uint8_t, 4> premult(geom::vector<std::uint8_t, 4> const & c)
+	{
+		return {
+			(static_cast<std::uint16_t>(c[0]) * c[3]) / 255,
+			(static_cast<std::uint16_t>(c[1]) * c[3]) / 255,
+			(static_cast<std::uint16_t>(c[2]) * c[3]) / 255,
+			c[3]
+		};
+	}
+
+	inline geom::vector<std::uint16_t, 4> premult(geom::vector<std::uint16_t, 4> const & c)
+	{
+		return {
+			(static_cast<std::uint32_t>(c[0]) * c[3]) / 65535,
+			(static_cast<std::uint32_t>(c[1]) * c[3]) / 65535,
+			(static_cast<std::uint32_t>(c[2]) * c[3]) / 65535,
+			c[3]
+		};
+	}
+
+	inline geom::vector<float, 4> unpremult(geom::vector<float, 4> const & c)
+	{
+		if (c[3] == 0.f)
+			return geom::vector<float, 4>::zero();
+
+		return {c[0] / c[3], c[1] / c[3], c[2] / c[3], c[3]};
+	}
+
+	inline geom::vector<std::uint8_t, 4> unpremult(geom::vector<std::uint8_t, 4> const & c)
+	{
+		if (c[3] == 0)
+			return geom::vector<std::uint8_t, 4>::zero();
+
+		return {
+			(static_cast<std::uint16_t>(c[0]) * 255) / c[3],
+			(static_cast<std::uint16_t>(c[1]) * 255) / c[3],
+			(static_cast<std::uint16_t>(c[2]) * 255) / c[3],
+			c[3]
+		};
+	}
+
+	inline geom::vector<std::uint16_t, 4> unpremult(geom::vector<std::uint16_t, 4> const & c)
+	{
+		if (c[3] == 0)
+			return geom::vector<std::uint16_t, 4>::zero();
+
+		return {
+			(static_cast<std::uint32_t>(c[0]) * 65535) / c[3],
+			(static_cast<std::uint32_t>(c[1]) * 65535) / c[3],
+			(static_cast<std::uint32_t>(c[2]) * 65535) / c[3],
+			c[3]
+		};
+	}
+
 	struct generic_color
 	{
 		color_4f c;