Improve calculation of brighter colors

The old code did not brighten up "pure" colors like "red", "green" and "blue"
at all. The new code use a different precomputed LUT which is based upon
simplified vector math, see the comments in FbTk/ColorLUT.cc

4 files changed, 209 insertions, 22 deletions

diff --git a/src/FbTk/ColorLUT.cc b/src/FbTk/ColorLUT.cc
index 97af8aa..9bcabf7 100644
--- a/src/FbTk/ColorLUT.cc
+++ b/src/FbTk/ColorLUT.cc
@@ -1,4 +1,4 @@
-// ColorLUT.cc for Fluxbox Window Manager 
+// ColorLUT.cc for Fluxbox Window Manager
 // Copyright (c) 2013 - Mathias Gumz <akira at fluxbox dot org>
 //
 // Permission is hereby granted, free of charge, to any person obtaining a
@@ -22,6 +22,7 @@
 
 #include "ColorLUT.hh"
 
+namespace FbTk {
 
 // created by:
 //
@@ -52,8 +53,7 @@
 // ./a.out 1.5 | xxd -i -c 8 # value + (value >> 1))
 //
 
-namespace FbTk {
-
+#if 0 // unused
 const unsigned char ColorLUT::PRE_MULTIPLY_1_5[256] = {
   0x00, 0x01, 0x03, 0x04, 0x06, 0x07, 0x09, 0x0a,
   0x0c, 0x0d, 0x0f, 0x10, 0x12, 0x13, 0x15, 0x16,
@@ -125,6 +125,7 @@ const unsigned char ColorLUT::PRE_MULTIPLY_1_125[256] = {
   0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
 };
 
+#endif
 
 // ./a.out 0.75 | xxd -i -c 8 # (value >> 1) + (value >> 2))
 const unsigned char ColorLUT::PRE_MULTIPLY_0_75[256] = {
@@ -162,5 +163,185 @@ const unsigned char ColorLUT::PRE_MULTIPLY_0_75[256] = {
   0xba, 0xba, 0xbb, 0xbc, 0xbd, 0xbd, 0xbe, 0xbf
 };
 
+
+
+// created by:
+//
+//   #include <math.h>
+//   #include <stdlib.h>
+//   #include <unistd.h>
+//
+//   int main(int argc, char const *argv[]) {
+//
+//       size_t i;
+//       unsigned char c;
+//       unsigned int v;
+//       unsigned int s = 4;
+//
+//       if (argc > 1) {
+//           s = atoi(argv[1]);
+//       }
+//
+//       for (i = 0; i < 256; ++i) {
+//           v = i + ((0xff - i) / s);
+//           c = (unsigned char)v;
+//           write(1, &c, 1);
+//       }
+//
+//       return 0;
+//   }
+//
+// math behind:
+//
+//  rgb-color-space forms a cube. to make
+//  something "brighter" one has to nudge a
+//  given color towards "white" (255, 255, 255).
+//  we use simple vector math to do this:
+//
+//    (nred  )   (red  )       ((255)   (red  ))
+//    (ngreen) = (green) + s * ((255) - (green))
+//    (nblue )   (blue )       ((255)   (blue ))
+//
+//  this approach is better than just multiplying
+//  a given color by a factor (ColorLUT::PRE_MULTIPLY*)
+//  example:
+//
+//    brighten_via_premultiply_*(#ff0000) = #ff0000
+//    brighten_via_brighter_4(#ff0000) = #ffef3f
+//
+//  right now the calculation of 's' is pretty
+//  straightforward: it is just 1/nth of the length
+//  of the vector-component. a more precise approach
+//  would calculate the length of the vector via
+//  sqrt(red * red + green * green + blue * blue) and
+//  scale that value down, allthough this would
+//  need either adhoc-computation or a more advanced
+//  lookup-table. right now the simple approach is
+//  sufficient.
+//
+//  to make a color "darker" one has to nudge the
+//  color towards "black" (0, 0, 0). the formula
+//  from above changes to
+//
+//    (nred) = (0) + s * ((red) - 0)
+//     ...
+//
+//   which simplifies down to (s * red) .. which is
+//   covered by PRE_MULTIPLY_0_75 already.
+
+
+// ./a.out 4 | xxd -i -c 8
+const unsigned char ColorLUT::BRIGHTER_4[256] = {
+  0x3f, 0x40, 0x41, 0x42, 0x42, 0x43, 0x44, 0x45,
+  0x45, 0x46, 0x47, 0x48, 0x48, 0x49, 0x4a, 0x4b,
+  0x4b, 0x4c, 0x4d, 0x4e, 0x4e, 0x4f, 0x50, 0x51,
+  0x51, 0x52, 0x53, 0x54, 0x54, 0x55, 0x56, 0x57,
+  0x57, 0x58, 0x59, 0x5a, 0x5a, 0x5b, 0x5c, 0x5d,
+  0x5d, 0x5e, 0x5f, 0x60, 0x60, 0x61, 0x62, 0x63,
+  0x63, 0x64, 0x65, 0x66, 0x66, 0x67, 0x68, 0x69,
+  0x69, 0x6a, 0x6b, 0x6c, 0x6c, 0x6d, 0x6e, 0x6f,
+  0x6f, 0x70, 0x71, 0x72, 0x72, 0x73, 0x74, 0x75,
+  0x75, 0x76, 0x77, 0x78, 0x78, 0x79, 0x7a, 0x7b,
+  0x7b, 0x7c, 0x7d, 0x7e, 0x7e, 0x7f, 0x80, 0x81,
+  0x81, 0x82, 0x83, 0x84, 0x84, 0x85, 0x86, 0x87,
+  0x87, 0x88, 0x89, 0x8a, 0x8a, 0x8b, 0x8c, 0x8d,
+  0x8d, 0x8e, 0x8f, 0x90, 0x90, 0x91, 0x92, 0x93,
+  0x93, 0x94, 0x95, 0x96, 0x96, 0x97, 0x98, 0x99,
+  0x99, 0x9a, 0x9b, 0x9c, 0x9c, 0x9d, 0x9e, 0x9f,
+  0x9f, 0xa0, 0xa1, 0xa2, 0xa2, 0xa3, 0xa4, 0xa5,
+  0xa5, 0xa6, 0xa7, 0xa8, 0xa8, 0xa9, 0xaa, 0xab,
+  0xab, 0xac, 0xad, 0xae, 0xae, 0xaf, 0xb0, 0xb1,
+  0xb1, 0xb2, 0xb3, 0xb4, 0xb4, 0xb5, 0xb6, 0xb7,
+  0xb7, 0xb8, 0xb9, 0xba, 0xba, 0xbb, 0xbc, 0xbd,
+  0xbd, 0xbe, 0xbf, 0xc0, 0xc0, 0xc1, 0xc2, 0xc3,
+  0xc3, 0xc4, 0xc5, 0xc6, 0xc6, 0xc7, 0xc8, 0xc9,
+  0xc9, 0xca, 0xcb, 0xcc, 0xcc, 0xcd, 0xce, 0xcf,
+  0xcf, 0xd0, 0xd1, 0xd2, 0xd2, 0xd3, 0xd4, 0xd5,
+  0xd5, 0xd6, 0xd7, 0xd8, 0xd8, 0xd9, 0xda, 0xdb,
+  0xdb, 0xdc, 0xdd, 0xde, 0xde, 0xdf, 0xe0, 0xe1,
+  0xe1, 0xe2, 0xe3, 0xe4, 0xe4, 0xe5, 0xe6, 0xe7,
+  0xe7, 0xe8, 0xe9, 0xea, 0xea, 0xeb, 0xec, 0xed,
+  0xed, 0xee, 0xef, 0xf0, 0xf0, 0xf1, 0xf2, 0xf3,
+  0xf3, 0xf4, 0xf5, 0xf6, 0xf6, 0xf7, 0xf8, 0xf9,
+  0xf9, 0xfa, 0xfb, 0xfc, 0xfc, 0xfd, 0xfe, 0xff
+};
+
+// ./a.out 8 | xxd -i -c 8
+const unsigned char ColorLUT::BRIGHTER_8[256] = {
+  0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26,
+  0x26, 0x27, 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d,
+  0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33, 0x34,
+  0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b,
+  0x3b, 0x3c, 0x3d, 0x3e, 0x3f, 0x40, 0x41, 0x42,
+  0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49,
+  0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f, 0x50,
+  0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57,
+  0x57, 0x58, 0x59, 0x5a, 0x5b, 0x5c, 0x5d, 0x5e,
+  0x5e, 0x5f, 0x60, 0x61, 0x62, 0x63, 0x64, 0x65,
+  0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c,
+  0x6c, 0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73,
+  0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a,
+  0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, 0x80, 0x81,
+  0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88,
+  0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f,
+  0x8f, 0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96,
+  0x96, 0x97, 0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d,
+  0x9d, 0x9e, 0x9f, 0xa0, 0xa1, 0xa2, 0xa3, 0xa4,
+  0xa4, 0xa5, 0xa6, 0xa7, 0xa8, 0xa9, 0xaa, 0xab,
+  0xab, 0xac, 0xad, 0xae, 0xaf, 0xb0, 0xb1, 0xb2,
+  0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7, 0xb8, 0xb9,
+  0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf, 0xc0,
+  0xc0, 0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7,
+  0xc7, 0xc8, 0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce,
+  0xce, 0xcf, 0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd5,
+  0xd5, 0xd6, 0xd7, 0xd8, 0xd9, 0xda, 0xdb, 0xdc,
+  0xdc, 0xdd, 0xde, 0xdf, 0xe0, 0xe1, 0xe2, 0xe3,
+  0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8, 0xe9, 0xea,
+  0xea, 0xeb, 0xec, 0xed, 0xee, 0xef, 0xf0, 0xf1,
+  0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8,
+  0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff
+};
+
+#if 0 // unused
+
+// ./a.out 4 | xxd -i -c 8
+const unsigned char ColorLUT::BRIGHTER_16[256] = {
+  0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16,
+  0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e,
+  0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25,
+  0x26, 0x27, 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d,
+  0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33, 0x34,
+  0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c,
+  0x3c, 0x3d, 0x3e, 0x3f, 0x40, 0x41, 0x42, 0x43,
+  0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b,
+  0x4b, 0x4c, 0x4d, 0x4e, 0x4f, 0x50, 0x51, 0x52,
+  0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a,
+  0x5a, 0x5b, 0x5c, 0x5d, 0x5e, 0x5f, 0x60, 0x61,
+  0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69,
+  0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70,
+  0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78,
+  0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f,
+  0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
+  0x87, 0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e,
+  0x8f, 0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96,
+  0x96, 0x97, 0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d,
+  0x9e, 0x9f, 0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5,
+  0xa5, 0xa6, 0xa7, 0xa8, 0xa9, 0xaa, 0xab, 0xac,
+  0xad, 0xae, 0xaf, 0xb0, 0xb1, 0xb2, 0xb3, 0xb4,
+  0xb4, 0xb5, 0xb6, 0xb7, 0xb8, 0xb9, 0xba, 0xbb,
+  0xbc, 0xbd, 0xbe, 0xbf, 0xc0, 0xc1, 0xc2, 0xc3,
+  0xc3, 0xc4, 0xc5, 0xc6, 0xc7, 0xc8, 0xc9, 0xca,
+  0xcb, 0xcc, 0xcd, 0xce, 0xcf, 0xd0, 0xd1, 0xd2,
+  0xd2, 0xd3, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8, 0xd9,
+  0xda, 0xdb, 0xdc, 0xdd, 0xde, 0xdf, 0xe0, 0xe1,
+  0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7, 0xe8,
+  0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef, 0xf0,
+  0xf0, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7,
+  0xf8, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff
+};
+
+#endif
+
+
 }
 
diff --git a/src/FbTk/ColorLUT.hh b/src/FbTk/ColorLUT.hh
index 66b8493..a9ff410 100644
--- a/src/FbTk/ColorLUT.hh
+++ b/src/FbTk/ColorLUT.hh
@@ -24,10 +24,18 @@ namespace FbTk {
 
 namespace ColorLUT {
 
+#if 0 // unused
 extern const unsigned char PRE_MULTIPLY_1_5[256];
 extern const unsigned char PRE_MULTIPLY_1_125[256];
+#endif
 extern const unsigned char PRE_MULTIPLY_0_75[256];
 
+extern const unsigned char BRIGHTER_4[256];
+extern const unsigned char BRIGHTER_8[256];
+#if 0 // unused
+extern const unsigned char BRIGHTER_16[256];
+#endif
+
 }
 
 }
diff --git a/src/FbTk/Texture.cc b/src/FbTk/Texture.cc
index da45bc4..888b3c7 100644
--- a/src/FbTk/Texture.cc
+++ b/src/FbTk/Texture.cc
@@ -37,7 +37,7 @@
 namespace {
 
 unsigned short inline brighten(unsigned short c) {
-    return 0x101 * FbTk::ColorLUT::PRE_MULTIPLY_1_5[c];
+    return 0x101 * FbTk::ColorLUT::BRIGHTER_8[c];
 }
 
 unsigned short inline darken(unsigned short c) {
diff --git a/src/FbTk/TextureRender.cc b/src/FbTk/TextureRender.cc
index f1addb4..8c7087f 100644
--- a/src/FbTk/TextureRender.cc
+++ b/src/FbTk/TextureRender.cc
@@ -49,9 +49,9 @@ using std::endl;
 using std::string;
 using std::max;
 using std::min;
-using FbTk::ColorLUT::PRE_MULTIPLY_1_5;
-using FbTk::ColorLUT::PRE_MULTIPLY_1_125;
 using FbTk::ColorLUT::PRE_MULTIPLY_0_75;
+using FbTk::ColorLUT::BRIGHTER_4;
+using FbTk::ColorLUT::BRIGHTER_8;
 
 namespace FbTk {
 
@@ -65,19 +65,17 @@ struct RGBA {
     // simple function-pointers for interlace-code
     // (and avoid *this 'overhead')
 
-    // 1.5 of current value, clamp to ~0 (0xff)
-    static void brighten_1_5(RGBA& color) {
-        color.r = PRE_MULTIPLY_1_5[color.r];
-        color.g = PRE_MULTIPLY_1_5[color.g];
-        color.b = PRE_MULTIPLY_1_5[color.b];
-    }
 
+    static void brighten_4(RGBA& color) {
+        color.r = BRIGHTER_4[color.r];
+        color.g = BRIGHTER_4[color.g];
+        color.b = BRIGHTER_4[color.b];
+    }
 
-    // 1.125 of current value
-    static void brighten_1_125(RGBA& color) {
-        color.r = PRE_MULTIPLY_1_125[color.r];
-        color.g = PRE_MULTIPLY_1_125[color.g];
-        color.b = PRE_MULTIPLY_1_125[color.b];
+    static void brighten_8(RGBA& color) {
+        color.r = BRIGHTER_8[color.r];
+        color.g = BRIGHTER_8[color.g];
+        color.b = BRIGHTER_8[color.b];
     }
 
     // 0.75 of old value
@@ -93,7 +91,7 @@ struct RGBA {
 };
 
 const RGBA::colorFunc RGBA::pseudoInterlaceFuncs[2] = {
-    RGBA::brighten_1_125,
+    RGBA::brighten_4,
     RGBA::darken
 };
 
@@ -287,13 +285,13 @@ void renderBevel1(bool interlaced,
     // brighten top line and first pixel of the
     // 2nd line
     for (i = 0; i < width + 1; ++i) {
-        FbTk::RGBA::brighten_1_5(rgba[i]);
+        FbTk::RGBA::brighten_4(rgba[i]);
     }
 
     // bright and darken left and right border
     for (i = 2 * width - 1; i < s - width; i += width) {
         FbTk::RGBA::darken(rgba[i]); // right border
-        FbTk::RGBA::brighten_1_5(rgba[i + 1]);  // left border on the next line
+        FbTk::RGBA::brighten_4(rgba[i + 1]);  // left border on the next line
     }
 
     // darken bottom line, except the first pixel
@@ -331,14 +329,14 @@ void renderBevel2(bool interlaced,
 
     // top line, but stop 2 pixels before right border
     for (i = (width + 1); i < ((2 * width) - 2); i++) {
-        FbTk::RGBA::brighten_1_5(rgba[i]);
+        FbTk::RGBA::brighten_4(rgba[i]);
     }
 
     // first darken the right border, then brighten the
     // left border
     for ( ; i < (s - (2 * width) - 1); i += width) {
         FbTk::RGBA::darken(rgba[i]);
-        FbTk::RGBA::brighten_1_5(rgba[i + 3]);
+        FbTk::RGBA::brighten_4(rgba[i + 3]);
     }
 
     // bottom line