Pass storage size to libass to fix rendering

Since ASS rendering depends on the storage size of the video libass
needs to know about it to render the subtitles correctly. If it isn't
told about the storage size libass uses the value from PlayRes{X,Y} as
a guess, but this isn't always correct.
With Aegisub currently always rendering at storage resolution
this ends up the same as the frame size.

Author: TheOneric

src/subtitles_provider_libass.cpp

@@ -170,6 +170,8 @@ LibassSubtitlesProvider::~LibassSubtitlesProvider() {
 
 void LibassSubtitlesProvider::DrawSubtitles(VideoFrame &frame,double time) {
 	ass_set_frame_size(renderer(), frame.width, frame.height);
+	// Note: this relies on Aegisub always rendering at video storage res
+	ass_set_storage_size(renderer(), frame.width, frame.height);
 
 	ASS_Image* img = ass_render_frame(renderer(), ass_track, int(time * 1000), nullptr);
 

vendor/csri/backends/libass/libass_csri.c

@@ -105,6 +105,8 @@ int csri_request_fmt(csri_inst *inst, const struct csri_fmt *fmt)
 	if (!csri_is_rgb(fmt->pixfmt) || csri_has_alpha(fmt->pixfmt))
 		return -1;
 	ass_set_frame_size(inst->ass_renderer, fmt->width, fmt->height);
+	// Note: this relies on CSRI always rendering at video storage res
+	ass_set_storage_size(inst->ass_renderer, fmt->width, fmt->height);
 	return 0;
 }