com32/lib/sys/vesa/alphatbl.pl

   1 #!/usr/bin/perl
   2 #
   3 # Produce gamma-correction tables for alpha blending, assuming sRGB space.
   4 #
   5
   6 sub srgb_to_linear($)
   7 {
   8     my($s) = @_;
   9
  10     if ($s <= 10) {
  11         return $s/(255*12.92);
  12     } else {
  13         return (($s+14.025)/269.025)**2.4;
  14     }
  15 }
  16
  17 sub linear_to_srgb($)
  18 {
  19     my($l) = @_;
  20     my $s;
  21
  22     if ($l <= 0.00304) {
  23         $s = 12.92*$l;
  24     } else {
  25         $s = 1.055*$l**(1.0/2.4) - 0.055;
  26     }
  27
  28     return int($s*255+0.5);
  29 }
  30
  31 # Header
  32 print "#include <inttypes.h>\n\n";
  33
  34 #
  35 # Table 1: convert 8-bit sRGB values to 16-bit linear values
  36 #
  37
  38 print "const uint16_t __vesacon_srgb_to_linear[256] = {\n";
  39 for ($i = 0; $i <= 255; $i++) {
  40     printf "\t%5d,\n", int(srgb_to_linear($i)*65535+0.5);
  41 }
  42 print "};\n\n";
  43
  44 #
  45 # Table 2: convert linear values in the range [0, 65535*255],
  46 #          shifted right by 12 bits, to sRGB
  47 #
  48
  49 print "const uint8_t __vesacon_linear_to_srgb[4080] = {\n";
  50 for ($i = 0; $i <= 4079; $i++) {
  51     printf "\t%3d,\n", linear_to_srgb(($i+0.5)/4079.937744);
  52 }
  53 print "};\n\n";