Francois Gouget : winetest/build-patterns: Take the distance between key colors into account.

[Alexandre Julliard]

Module: tools
Branch: master
Commit: e527645adc6e2b145428087afb1b68215f9e1840
URL:    https://source.winehq.org/git/tools.git/?a=commit;h=e527645adc6e2b145428087afb1b68215f9e1840

Author: Francois Gouget <fgouget at codeweavers.com>
Date:   Tue Aug 31 15:39:59 2021 +0200

winetest/build-patterns: Take the distance between key colors into account.

To get a uniform color gradient, fewer colors should be squeezed between
close key colors than between distant ones.

Signed-off-by: Francois Gouget <fgouget at codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard at winehq.org>

---

 winetest/build-patterns | 35 ++++++++++++++++++++++++++++-------
 1 file changed, 28 insertions(+), 7 deletions(-)

diff --git a/winetest/build-patterns b/winetest/build-patterns
index 2ee5d5b..ff72516 100755
--- a/winetest/build-patterns
+++ b/winetest/build-patterns
@@ -872,6 +872,13 @@ sub blend($$$)
     return $r;
 }
 
+sub distance($$)
+{
+    my ($a, $b) = @_;
+    return sqrt(($b->[0] - $a->[0])**2 +
+                ($b->[1] - $a->[1])**2 +
+                ($b->[2] - $a->[2])**2);
+}
 
 # Use colors to differentiate the set values. Each unique value is assigned
 # a color (in HTML format) picked along a series of gradients passing by the
@@ -897,19 +904,33 @@ sub compute_set_colors($)
         # when many colors are needed.
         $keycolors[0] = [0, 179, 179] if ($count > 10);
 
+        # Compute the total length of the path traced by the key colors through
+        # the colorspace. This is necessary so the gradient remains uniform
+        # even if two key colors are close to each other. This does assume that
+        # the path does not zigzag too much: (0,0,0)->(255,0,0)->(1,0,0) cannot
+        # produce a meaningful gradient.
+        my @keypos = (0);
+        for (my $i = 1; $i < @keycolors; $i++)
+        {
+            my $d = distance($keycolors[$i - 1], $keycolors[$i]);
+            $keypos[$i] = $keypos[$i - 1] + $d;
+        }
+
         my $k = 0;
-        my ($start, $end) = (-1, 0);
         for (0..$count-1)
         {
-            while (!$end or $_ > $end)
+            # Compute the position of the current item on the path
+            my $pos = $_ / ($count - 1) * $keypos[-1];
+
+            # Figure out which segment of the path this corresponds to
+            while ($pos > $keypos[$k+1] and $k+1 < @keycolors-1)
             {
                 $k++;
-                $start = $end;
-                $end = ($count-1) * $k / (@keycolors-1);
             }
-            $set->{$values[$_]} = color2html(blend(($_-$start)/($end-$start),
-                                                   $keycolors[$k-1],
-                                                   $keycolors[$k]));
+
+            # And blend
+            my $Rgb = blend(($pos - $keypos[$k]) / ($keypos[$k+1] - $keypos[$k]), $keycolors[$k], $keycolors[$k+1]);
+            $set->{$values[$_]} = color2html($Rgb);
         }
     }
 }