From: Carl Hetherington <cth@carlh.net>
Date: Sun, 3 Sep 2023 16:33:19 +0000 (+0200)
Subject: Make scale_for_display less likely to leave confusing gaps (#2589).
X-Git-Url: https://git.carlh.net/gitweb/?p=dcpomatic.git;a=commitdiff_plain;h=refs%2Fheads%2F2589-lines

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

diff --git a/src/lib/util.cc b/src/lib/util.cc
index 4ec425d40..a80f86c3e 100644
--- 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;
 }
 
 
diff --git a/test/util_test.cc b/test/util_test.cc
index 49d0b3bc2..59dfb5c90 100644
--- a/test/util_test.cc
+++ b/test/util_test.cc
@@ -155,3 +155,23 @@ BOOST_AUTO_TEST_CASE(word_wrap_test)
 	BOOST_CHECK(word_wrap("hello this is a longer bit of text and it should be word-wrapped", 31) == string{"hello this is a longer bit of \ntext and it should be word-\nwrapped\n"});
 	BOOST_CHECK_EQUAL(word_wrap("hellocan'twrapthissadly", 5), "hello\ncan't\nwrapt\nhissa\ndly\n");
 }
+
+
+BOOST_AUTO_TEST_CASE(scale_for_display_test)
+{
+	/* 1998x1076 image in a flat frame, displayed in 1104x596.
+	 * In the DCP there will be 2px black top and bottom.
+	 * So the display width should definitely be 1104, and it then follows that
+	 * the display height should be scaled by the same factor as the width has been.
+	 */
+	BOOST_CHECK(scale_for_display(dcp::Size(1998, 1076), dcp::Size(1104, 596), dcp::Size(1998, 1080), PixelQuanta(2, 2)) == dcp::Size(1104, 594));
+
+	/* 1800x1080 image in a flat frame, displayed in 1104x596.
+	 * In the DCP there should be 99px black left and right.
+	 * So the display height should definitely be 596.
+	 */
+	BOOST_CHECK(scale_for_display(dcp::Size(1800, 1080), dcp::Size(1104, 596), dcp::Size(1998, 1080), PixelQuanta(2, 2)) == dcp::Size(994, 596));
+
+	/* This happens sometimes as windows are getting resized */
+	BOOST_CHECK(scale_for_display(dcp::Size(1998, 1076), dcp::Size(64, 64), dcp::Size(1998, 1080), PixelQuanta(2, 2)) == dcp::Size(64, 34));
+}