Fix subtitle vertical position (#2367).

Previously we would not account for the differences in what vertical
position means between Interop and SMPTE.  For interop, vertical
position is the distance from the reference point to the text
baseline, whereas for SMPTE it is the distance from the reference
point to the top/middle/bottom of the subtitle (depending on the
reference).

This caused differences between the preview and the DCP for some
cases (notably, using SRT/SSA and making Interop DCPs, or converting
Interop DCP subs to SMPTE, or vice versa).

1 files changed, 64 insertions, 4 deletions

diff --git a/src/lib/render_text.cc b/src/lib/render_text.cc
index 9c1c233c2..d3db4ac19 100644
--- a/src/lib/render_text.cc
+++ b/src/lib/render_text.cc
@@ -171,12 +171,12 @@ create_surface (shared_ptr<Image> image)
 
 
 static string
-setup_font (StringText const& subtitle)
+setup_font(shared_ptr<const dcpomatic::Font> font)
 {
 	auto font_file = default_font_file ();
 
-	if (subtitle.font && subtitle.font->file()) {
-		font_file = *subtitle.font->file();
+	if (font && font->file()) {
+		font_file = *font->file();
 	}
 
 	return FontConfig::instance()->make_font_available(font_file);
@@ -299,7 +299,7 @@ render_line (list<StringText> subtitles, dcp::Size target, DCPTime time, int fra
 	DCPOMATIC_ASSERT (!subtitles.empty ());
 	auto const& first = subtitles.front ();
 
-	auto const font_name = setup_font (first);
+	auto const font_name = setup_font(first.font);
 	auto const fade_factor = calculate_fade_factor (first, time, frame_rate);
 	auto const markup = marked_up (subtitles, target.height, fade_factor, font_name);
 	auto layout = create_layout ();
@@ -402,3 +402,63 @@ render_text (list<StringText> subtitles, dcp::Size target, DCPTime time, int fra
 
 	return images;
 }
+
+
+float
+FontMetrics::height(StringText const& subtitle)
+{
+	return get(subtitle)->second.second;
+}
+
+
+float
+FontMetrics::baseline_to_bottom(StringText const& subtitle)
+{
+	return get(subtitle)->second.first;
+}
+
+
+FontMetrics::Cache::iterator
+FontMetrics::get(StringText const& subtitle)
+{
+	auto id = Identifier(subtitle);
+
+	auto iter = _cache.find(id);
+	if (iter != _cache.end()) {
+		return iter;
+	}
+
+	auto const font_name = setup_font(subtitle.font);
+	auto layout = create_layout();
+	auto copy = subtitle;
+	copy.set_text("Qypjg");
+	setup_layout(layout, font_name, marked_up({copy}, _target_height, 1, font_name));
+	auto ink = layout->get_ink_extents();
+	auto const scale = float(_target_height * Pango::SCALE);
+	return _cache.insert({id, { ink.get_y() / scale, ink.get_height() / scale}}).first;
+}
+
+
+FontMetrics::Identifier::Identifier(StringText const& subtitle)
+	: font(subtitle.font)
+	, size(subtitle.size())
+	, aspect_adjust(subtitle.aspect_adjust())
+{
+
+}
+
+
+bool
+FontMetrics::Identifier::operator<(FontMetrics::Identifier const& other) const
+{
+	if (font != other.font) {
+		return font < other.font;
+	}
+
+	if (size != other.size) {
+	    return size < other.size;
+	}
+
+	return aspect_adjust < other.aspect_adjust;
+}
+