1 files changed, 47 insertions, 0 deletions
diff --git a/colour.c b/colour.c
new file mode 100644
index 0000000..8b5c401
--- /dev/null
+++ b/colour.c
@@ -0,0 +1,47 @@
+/* See LICENSE file for copyright and license details. */
+#include "common.h"
+
+
+double
+srgb_encode_unsigned(double t)
+{
+	return t <= 0.0031306684425217108
+		? 12.92 * t
+		: fma(1.055, pow(t, 1 / 2.4), -0.055);
+}
+
+double
+srgb_decode_unsigned(double t)
+{
+	return t <= 0.0031306684425217108 * 12.92
+		? t / 12.92
+		: pow((t + 0.055) / 1.055, 2.4);
+}
+
+
+double
+srgb_blend(double at0, double t, double at1)
+{
+	at0 = srgb_decode_unsigned(at0);
+	at1 = srgb_decode_unsigned(at1);
+	return srgb_encode_unsigned(fma((1 - t), at0, t * at1));
+}
+
+
+void
+set_source_colour_blend(cairo_t *g, const GdkColor *at0, double t, const GdkColor *at1)
+{
+	double max   = (double)UINT16_MAX;
+	double red   = srgb_blend(at0->red   / max, t, at1->red   / max);
+	double green = srgb_blend(at0->green / max, t, at1->green / max);
+	double blue  = srgb_blend(at0->blue  / max, t, at1->blue  / max);
+	cairo_set_source_rgb(g, red, green, blue);
+}
+
+
+void
+set_source_colour(cairo_t *g, const GdkColor *colour)
+{
+	double max = (double)UINT16_MAX;
+	cairo_set_source_rgb(g, colour->red / max, colour->green / max, colour->blue / max);
+}