ref: 6d8fbc2953c6ae29ee5162ca04920d6cef85d0ce
parent: 32219aaa35b07d6abceb7df9f802c9758b53eb72
author: rodri <rgl@antares-labs.eu>
date: Thu Jul 4 10:57:00 EDT 2024
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.
--- /dev/null
+++ b/color.c
@@ -1,0 +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;
+}
--- a/graphics.h
+++ b/graphics.h
@@ -339,6 +339,10 @@
Point3 modulapt3(Point3, Point3);
Memimage *rgb(ulong);
+/* color */
+Color srgb2linear(Color);
+Color linear2srgb(Color);
+
/* shadeop */
double sign(double);
double step(double, double);
--- a/mkfile
+++ b/mkfile
@@ -13,6 +13,7 @@
alloc.$O\
fb.$O\
shadeop.$O\
+ color.$O\
util.$O\
nanosec.$O\
--- a/render.c
+++ b/render.c
@@ -41,9 +41,9 @@
ulong *dst;
dst = fb->cb;
- dc = ul2col(dst[Dx(fb->r)*p.y + p.x]);
+ dc = srgb2linear(ul2col(dst[Dx(fb->r)*p.y + p.x]));
c = lerp3(dc, c, c.a); /* SoverD */
- dst[Dx(fb->r)*p.y + p.x] = col2ul(c);
+ dst[Dx(fb->r)*p.y + p.x] = col2ul(linear2srgb(c));
}
static void
--- a/texture.c
+++ b/texture.c
@@ -29,18 +29,6 @@
}
static Color
-ul2col(ulong l)
-{- Color c;
-
- c.a = (l & 0xff)/255.0;
- c.b = (l>>8 & 0xff)/255.0;
- c.g = (l>>16 & 0xff)/255.0;
- c.r = (l>>24 & 0xff)/255.0;
- return c;
-}
-
-static Color
cbuf2col(uchar b[4])
{Color c;
@@ -72,7 +60,11 @@
break;
}
- return cbuf2col(cbuf);
+ /* TODO
+ * not all textures require color space conversion. implement a better
+ * interface to let the user decide.
+ */
+ return srgb2linear(cbuf2col(cbuf));
}
/*