fix fog/colormodability evaluation

[xonotic/darkplaces.git] / fogeval.pl

diff --git a/fogeval.pl b/fogeval.pl
new file mode 100644 (file)
index 0000000..a363320
--- /dev/null
+++ b/fogeval.pl
@@ -0,0 +1,125 @@
+use strict;
+use warnings;
+
+# generates the blendfunc flags function in gl_rmain.c
+
+my %blendfuncs =
+(
+       GL_ONE                 => sub { (1, 1); },
+       GL_ZERO                => sub { (0, 0); },
+       GL_SRC_COLOR           => sub { ($_[0], $_[1]); },
+       GL_ONE_MINUS_SRC_COLOR => sub { (1-$_[0], 1-$_[1]); },
+       GL_SRC_ALPHA           => sub { ($_[1], $_[1]); },
+       GL_ONE_MINUS_SRC_ALPHA => sub { (1-$_[1], 1-$_[1]); },
+       GL_DST_COLOR           => sub { ($_[2], $_[3]); },
+       GL_ONE_MINUS_DST_COLOR => sub { (1-$_[2], 1-$_[3]); },
+       GL_DST_ALPHA           => sub { ($_[3], $_[3]); },
+       GL_ONE_MINUS_DST_ALPHA => sub { (1-$_[3], 1-$_[3]); },
+);
+
+sub evalblend($$$$$$)
+{
+       my ($fs, $fd, $s, $sa, $d, $da) = @_;
+       my @fs = $fs->($s, $sa, $d, $da);
+       my @fd = $fd->($s, $sa, $d, $da);
+       return (
+               $fs[0] * $s  + $fd[0] * $d,
+               $fs[1] * $sa + $fd[1] * $da
+       );
+}
+
+sub isinvariant($$$$)
+{
+       my ($fs, $fd, $s, $sa) = @_;
+       my ($d, $da) = (0.7823, 0.3289);
+       my ($out, $outa) = evalblend $fs, $fd, $s, $sa, $d, $da;
+       return abs($out - $d) < 0.001 && abs($outa - $da) < 0.001;
+}
+
+sub isfogfriendly($$$$$)
+{
+       my ($fs, $fd, $s, $sa, $foghack) = @_;
+       my ($d, $da) = (0.7823, 0.3289);
+       my $fogamount = 0.3237;
+       my $fogcolor = 0.8612;
+
+       # compare:
+       # 1. blend(fog(s), sa, fog(d), da)
+       # 2. fog(blend(s, sa, d, da))
+
+       my ($out1, $out1a) = evalblend $fs, $fd, $s + ((defined $foghack ? $foghack < 0 ? $s : $foghack : $fogcolor) - $s) * $fogamount, $sa, $d + ($fogcolor - $d) * $fogamount, $da;
+       my ($out2, $out2a) = evalblend $fs, $fd, $s, $sa, $d, $da;
+               $out2 = $out2 + ($fogcolor - $out2) * $fogamount;
+
+       return abs($out1 - $out2) < 0.001 && abs($out1a - $out2a) < 0.001;
+}
+
+#die isfogfriendly $blendfuncs{GL_ONE}, $blendfuncs{GL_ONE}, 1, 0, 0;
+# out1 = 0 + fog($d)
+# out2 = fog(1 + $d)
+
+sub willitblend($$)
+{
+       my ($fs, $fd) = @_;
+       for my $s(0, 0.25, 0.5, 0.75, 1)
+       {
+               for my $sa(0, 0.25, 0.5, 0.75, 1)
+               {
+                       if(isinvariant($fs, $fd, $s, $sa))
+                       {
+                               if(!isinvariant($fs, $fd, 0, $sa))
+                               {
+                                       return 0; # no colormod possible
+                               }
+                       }
+               }
+       }
+       return 1;
+}
+
+sub willitfog($$)
+{
+       my ($fs, $fd) = @_;
+
+       FOGHACK:
+       for my $foghack(undef, 0, 1, -1)
+       {
+               for my $s(0, 0.25, 0.5, 0.75, 1)
+               {
+                       for my $sa(0, 0.25, 0.5, 0.75, 1)
+                       {
+                               if(!isfogfriendly($fs, $fd, $s, $sa, $foghack))
+                               {
+                                       next FOGHACK;
+                               }
+                       }
+               }
+               return (1, $foghack);
+       }
+       return (0, undef);
+}
+
+print "\tr |= BLENDFUNC_ALLOWS_COLORMOD;\n";
+for my $s(sort keys %blendfuncs)
+{
+       for my $d(sort keys %blendfuncs)
+       {
+               if(!willitblend $blendfuncs{$s}, $blendfuncs{$d})
+               {
+                       print "\tif(src == $s && dst == $d) r &= ~BLENDFUNC_ALLOWS_COLORMOD;\n";
+               }
+               my ($result, $h) = willitfog $blendfuncs{$s}, $blendfuncs{$d};
+               if($result)
+               {
+                       if(defined $h)
+                       {
+                               print "\tif(src == $s && dst == $d) r |= BLENDFUNC_ALLOWS_FOG_HACK$h;\n";
+                       }
+                       else
+                       {
+                               print "\tif(src == $s && dst == $d) r |= BLENDFUNC_ALLOWS_FOG;\n";
+                       }
+               }
+       }
+}
+