Add option to limit canvas size

JSO struggles with complex subtitles on HiDPI canvasses,
so limiting the size can make sense if such subtitles are expected.

This was ported from jellyfin's fork and jellyfin-web uses this on at
least some devices. In the original implementation prescaleHeightLimit
would override hardHeightLimit if it was larger. This undocumentend
behaviour was dropped here as it seemed unintuitive and unhelpful.

[Vasily <[email protected]>]
  Original implementation together with prescaling in
  jellyfin@345d701
  jellyfin@4c5f018
[Dmitry Lyzo]
  Rebased for upstream; seperated from the prescaling;
  removed default height limit and added docs
[Oneric]
  Removed prescaleHeightLimit overriding hardHeightLimit if larger;
  split hard height limit from prescaling.

Co-Authored-By: Dmitry Lyzo <[email protected]>

Author: 2 people

README.md

@@ -137,6 +137,9 @@ When creating an instance of SubtitleOctopus, you can set the following options:
                     (Default: `1.0` - no scaling; must be a number > 0)
 - `prescaleHeightLimit`: The height beyond which the subtitles canvas won't be prescaled.
                          (Default: `1080`)
+- `hardHeightLimit`: The maximum rendering height of the subtitles canvas.
+                     Beyond this subtitles will be upscaled by the browser.
+                     (Default: `0` - no limit)
 
 ### Rendering Modes
 #### JS Blending

src/subtitles-octopus.js

@@ -19,6 +19,7 @@ var SubtitlesOctopus = function (options) {
     self.targetFps = options.targetFps || 24;
     self.prescaleFactor = options.prescaleFactor || 1.0;
     self.prescaleHeightLimit = options.prescaleHeightLimit || 1080;
+    self.hardHeightLimit = options.hardHeightLimit || 0; // 0 - no limit
     self.isOurCanvas = false; // (internal) we created canvas and manage it
     self.video = options.video; // HTML video element (optional if canvas specified)
     self.canvasParent = null; // (internal) HTML canvas parent element
@@ -408,6 +409,7 @@ var SubtitlesOctopus = function (options) {
 
     function _computeCanvasSize(width, height) {
         var scalefactor = self.prescaleFactor <= 0 ? 1.0 : self.prescaleFactor;
+        var hardHeightLimit = self.hardHeightLimit <= 0 ? height : self.hardHeightLimit;
 
         if (height == 0) {
             width = 0;
@@ -418,6 +420,8 @@ var SubtitlesOctopus = function (options) {
                 newH *= self.prescaleFactor;
             else if (sgn * newH < sgn * self.prescaleHeightLimit)
                 newH = self.prescaleHeightLimit;
+            if (newH > hardHeightLimit)
+                newH = hardHeightLimit;
 
             width *= newH / height;
             height = newH;