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#!/usr/bin/perl
#
# Produce gamma-correction tables for alpha blending, assuming sRGB space.
#
sub srgb_to_linear($)
{
my($s) = @_;
if ($s <= 10) {
return $s/(255*12.92);
} else {
return (($s+14.025)/269.025)**2.4;
}
}
sub linear_to_srgb($)
{
my($l) = @_;
my $s;
if ($l <= 0.00304) {
$s = 12.92*$l;
} else {
$s = 1.055*$l**(1.0/2.4) - 0.055;
}
return int($s*255+0.5);
}
# Header
print "#include <inttypes.h>\n\n";
#
# Table 1: convert 8-bit sRGB values to 16-bit linear values
#
print "const uint16_t __vesacon_srgb_to_linear[256] = {\n";
for ($i = 0; $i <= 255; $i++) {
printf "\t%5d,\n", int(srgb_to_linear($i)*65535+0.5);
}
print "};\n\n";
#
# Table 2: convert linear values in the range [0, 65535*255],
# shifted right by 12 bits, to sRGB
#
print "const uint8_t __vesacon_linear_to_srgb[4080] = {\n";
for ($i = 0; $i <= 4079; $i++) {
printf "\t%3d,\n", linear_to_srgb(($i+0.5)/4079.937744);
}
print "};\n\n";
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