rough color space conversion implementation.

colors are now properly processed in linear RGB space for
lighting, shading and blending. sRGB is assumed for any
texture sampled and the destination framebuffer.

it's not perfect, but it does the job for now.

1 files changed, 138 insertions, 0 deletions

diff --git a/color.c b/color.c
new file mode 100644
index 0000000..cdd089f
--- /dev/null
+++ b/color.c
@@ -0,0 +1,138 @@
+#include <u.h>
+#include <libc.h>
+#include <thread.h>
+#include <draw.h>
+#include <memdraw.h>
+#include <geometry.h>
+#include "libobj/obj.h"
+#include "graphics.h"
+#include "internal.h"
+
+/*
+ * generated with:
+ * 	% seq 0 255 | awk '{$0 = $0/255; if($0 > 0.04045) $0 = (($0+0.055)/1.055)^2.4; else $0 = $0/12.92; printf("\t0x%02X,%s", int($0*255+0.5), NR%8 == 0? "\n": "")}'
+ */
+static uchar srgb2lineartab[] = {
+	0x00,	0x00,	0x00,	0x00,	0x00,	0x00,	0x00,	0x01,
+	0x01,	0x01,	0x01,	0x01,	0x01,	0x01,	0x01,	0x01,
+	0x01,	0x01,	0x02,	0x02,	0x02,	0x02,	0x02,	0x02,
+	0x02,	0x02,	0x03,	0x03,	0x03,	0x03,	0x03,	0x03,
+	0x04,	0x04,	0x04,	0x04,	0x04,	0x05,	0x05,	0x05,
+	0x05,	0x06,	0x06,	0x06,	0x06,	0x07,	0x07,	0x07,
+	0x08,	0x08,	0x08,	0x08,	0x09,	0x09,	0x09,	0x0A,
+	0x0A,	0x0A,	0x0B,	0x0B,	0x0C,	0x0C,	0x0C,	0x0D,
+	0x0D,	0x0D,	0x0E,	0x0E,	0x0F,	0x0F,	0x10,	0x10,
+	0x11,	0x11,	0x11,	0x12,	0x12,	0x13,	0x13,	0x14,
+	0x14,	0x15,	0x16,	0x16,	0x17,	0x17,	0x18,	0x18,
+	0x19,	0x19,	0x1A,	0x1B,	0x1B,	0x1C,	0x1D,	0x1D,
+	0x1E,	0x1E,	0x1F,	0x20,	0x20,	0x21,	0x22,	0x23,
+	0x23,	0x24,	0x25,	0x25,	0x26,	0x27,	0x28,	0x29,
+	0x29,	0x2A,	0x2B,	0x2C,	0x2D,	0x2D,	0x2E,	0x2F,
+	0x30,	0x31,	0x32,	0x33,	0x33,	0x34,	0x35,	0x36,
+	0x37,	0x38,	0x39,	0x3A,	0x3B,	0x3C,	0x3D,	0x3E,
+	0x3F,	0x40,	0x41,	0x42,	0x43,	0x44,	0x45,	0x46,
+	0x47,	0x48,	0x49,	0x4A,	0x4C,	0x4D,	0x4E,	0x4F,
+	0x50,	0x51,	0x52,	0x54,	0x55,	0x56,	0x57,	0x58,
+	0x5A,	0x5B,	0x5C,	0x5D,	0x5F,	0x60,	0x61,	0x63,
+	0x64,	0x65,	0x67,	0x68,	0x69,	0x6B,	0x6C,	0x6D,
+	0x6F,	0x70,	0x72,	0x73,	0x74,	0x76,	0x77,	0x79,
+	0x7A,	0x7C,	0x7D,	0x7F,	0x80,	0x82,	0x83,	0x85,
+	0x86,	0x88,	0x8A,	0x8B,	0x8D,	0x8E,	0x90,	0x92,
+	0x93,	0x95,	0x97,	0x98,	0x9A,	0x9C,	0x9D,	0x9F,
+	0xA1,	0xA3,	0xA4,	0xA6,	0xA8,	0xAA,	0xAB,	0xAD,
+	0xAF,	0xB1,	0xB3,	0xB5,	0xB7,	0xB8,	0xBA,	0xBC,
+	0xBE,	0xC0,	0xC2,	0xC4,	0xC6,	0xC8,	0xCA,	0xCC,
+	0xCE,	0xD0,	0xD2,	0xD4,	0xD6,	0xD8,	0xDA,	0xDC,
+	0xDE,	0xE0,	0xE2,	0xE5,	0xE7,	0xE9,	0xEB,	0xED,
+	0xEF,	0xF2,	0xF4,	0xF6,	0xF8,	0xFA,	0xFD,	0xFF,
+};
+
+/*
+ * generated with:
+ * 	% seq 0 255 | awk '{$0 = $0/255.0; if($0 > 0.0031308) $0 = 1.055*$0^(1.0/2.4)-0.055; else $0 = $0*12.92; printf("\t0x%02X,%s", int($0*255+0.5), NR%8 == 0? "\n": "")}'
+ */
+static uchar linear2srgbtab[] = {
+	0x00,	0x0D,	0x16,	0x1C,	0x22,	0x26,	0x2A,	0x2E,
+	0x32,	0x35,	0x38,	0x3B,	0x3D,	0x40,	0x42,	0x45,
+	0x47,	0x49,	0x4B,	0x4D,	0x4F,	0x51,	0x53,	0x55,
+	0x56,	0x58,	0x5A,	0x5C,	0x5D,	0x5F,	0x60,	0x62,
+	0x63,	0x65,	0x66,	0x68,	0x69,	0x6A,	0x6C,	0x6D,
+	0x6E,	0x70,	0x71,	0x72,	0x73,	0x75,	0x76,	0x77,
+	0x78,	0x79,	0x7A,	0x7C,	0x7D,	0x7E,	0x7F,	0x80,
+	0x81,	0x82,	0x83,	0x84,	0x85,	0x86,	0x87,	0x88,
+	0x89,	0x8A,	0x8B,	0x8C,	0x8D,	0x8E,	0x8F,	0x90,
+	0x91,	0x92,	0x93,	0x94,	0x94,	0x95,	0x96,	0x97,
+	0x98,	0x99,	0x9A,	0x9B,	0x9B,	0x9C,	0x9D,	0x9E,
+	0x9F,	0x9F,	0xA0,	0xA1,	0xA2,	0xA3,	0xA3,	0xA4,
+	0xA5,	0xA6,	0xA7,	0xA7,	0xA8,	0xA9,	0xAA,	0xAA,
+	0xAB,	0xAC,	0xAD,	0xAD,	0xAE,	0xAF,	0xAF,	0xB0,
+	0xB1,	0xB2,	0xB2,	0xB3,	0xB4,	0xB4,	0xB5,	0xB6,
+	0xB6,	0xB7,	0xB8,	0xB9,	0xB9,	0xBA,	0xBB,	0xBB,
+	0xBC,	0xBD,	0xBD,	0xBE,	0xBE,	0xBF,	0xC0,	0xC0,
+	0xC1,	0xC2,	0xC2,	0xC3,	0xC4,	0xC4,	0xC5,	0xC5,
+	0xC6,	0xC7,	0xC7,	0xC8,	0xC8,	0xC9,	0xCA,	0xCA,
+	0xCB,	0xCB,	0xCC,	0xCD,	0xCD,	0xCE,	0xCE,	0xCF,
+	0xD0,	0xD0,	0xD1,	0xD1,	0xD2,	0xD2,	0xD3,	0xD4,
+	0xD4,	0xD5,	0xD5,	0xD6,	0xD6,	0xD7,	0xD7,	0xD8,
+	0xD8,	0xD9,	0xDA,	0xDA,	0xDB,	0xDB,	0xDC,	0xDC,
+	0xDD,	0xDD,	0xDE,	0xDE,	0xDF,	0xDF,	0xE0,	0xE0,
+	0xE1,	0xE2,	0xE2,	0xE3,	0xE3,	0xE4,	0xE4,	0xE5,
+	0xE5,	0xE6,	0xE6,	0xE7,	0xE7,	0xE8,	0xE8,	0xE9,
+	0xE9,	0xEA,	0xEA,	0xEB,	0xEB,	0xEC,	0xEC,	0xED,
+	0xED,	0xEE,	0xEE,	0xEE,	0xEF,	0xEF,	0xF0,	0xF0,
+	0xF1,	0xF1,	0xF2,	0xF2,	0xF3,	0xF3,	0xF4,	0xF4,
+	0xF5,	0xF5,	0xF6,	0xF6,	0xF6,	0xF7,	0xF7,	0xF8,
+	0xF8,	0xF9,	0xF9,	0xFA,	0xFA,	0xFB,	0xFB,	0xFB,
+	0xFC,	0xFC,	0xFD,	0xFD,	0xFE,	0xFE,	0xFF,	0xFF,
+};
+
+/*
+ * Equations 5.32 and 5.30 from “Display Encoding”, Real-Time Rendering 4th ed. § 5.6
+ */
+//static double
+//_srgb2linear(double c)
+//{
+//	if(c > 0.04045)
+//		return pow((c + 0.055)/1.055, 2.4);
+//	return c/12.92;
+//}
+//
+//static double
+//_linear2srgb(double c)
+//{
+//	if(c > 0.0031308)
+//		return 1.055*pow(c, 1.0/2.4) - 0.055;
+//	return 12.92*c;
+//}
+
+static double
+_srgb2linear(double c)
+{
+	c = fclamp(c, 0, 1);
+	return srgb2lineartab[(int)(c*255)]/255.0;
+}
+
+static double
+_linear2srgb(double c)
+{
+	c = fclamp(c, 0, 1);
+	return linear2srgbtab[(int)(c*255)]/255.0;
+}
+
+Color
+srgb2linear(Color c)
+{
+	c.r = _srgb2linear(c.r);
+	c.g = _srgb2linear(c.g);
+	c.b = _srgb2linear(c.b);
+	return c;
+}
+
+Color
+linear2srgb(Color c)
+{
+	c.r = _linear2srgb(c.r);
+	c.g = _linear2srgb(c.g);
+	c.b = _linear2srgb(c.b);
+	return c;
+}