Make scale_for_display less likely to leave confusing gaps (#2589).

[dcpomatic.git] / src / lib / util.cc

diff --git a/src/lib/util.cc b/src/lib/util.cc
index 4ec425d40920b7d60b5bb555b4730c24bb28ed48..a80f86c3ec7fb6e9333511d002a4fe55d3dd2ad7 100644 (file)
--- a/src/lib/util.cc
+++ b/src/lib/util.cc
@@ -982,19 +982,25 @@ copy_in_bits (boost::filesystem::path from, boost::filesystem::path to, std::fun
 dcp::Size
 scale_for_display (dcp::Size s, dcp::Size display_container, dcp::Size film_container, PixelQuanta quanta)
 {
-       /* Now scale it down if the display container is smaller than the film container */
-       if (display_container != film_container) {
-               float const scale = min (
-                       float (display_container.width) / film_container.width,
-                       float (display_container.height) / film_container.height
+       if (std::abs(display_container.ratio() - film_container.ratio()) < 0.01) {
+               /* The display ratio is very close to what it should be, but it might not be exactly the same.
+                * Allow the image to stretch slightly (differently in x and y) so that we are less likely
+                * to get single pixel gaps in the preview.
+                */
+               return quanta.round(
+                       static_cast<float>(s.width) * display_container.width / film_container.width,
+                       static_cast<float>(s.height) * display_container.height / film_container.height
                        );
-
-               s.width = lrintf (s.width * scale);
-               s.height = lrintf (s.height * scale);
-               s = quanta.round (s);
+       } else {
+               /* The display ratio is quite different to the film, so scale it so that the dimension
+                * that needs to fit does fit.
+                */
+               auto const scale = min(
+                       static_cast<float>(display_container.width) / film_container.width,
+                       static_cast<float>(display_container.height) / film_container.height
+                       );
+               return quanta.round(s.width * scale, s.height * scale);
        }
-
-       return s;
 }