Add dropAllAnimations feature

Original implementation by JustAMan, mostly in the following
three commits sans unrelated changes. Backported by Oneric.
jellyfin@d3bc472
jellyfin@a66e797
jellyfin@971a997

The commits have also been adjusted to apply on top of current upstream
master, to use the animations detection from the previous commit instead
of the faulty original logic and the scanned_events variable was added.
Also added documentation which was missing in the original commits.

Co-authored-by: Oneric <oneric@oneric.stub>

Author: JustAMan

README.md

@@ -140,6 +140,12 @@ When creating an instance of SubtitleOctopus, you can set the following options:
 - `maxRenderHeight`: The maximum rendering height of the subtitles canvas.
                      Beyond this subtitles will be upscaled by the browser.
                      (Default: `0` - no limit)
+- `dropAllAnimations`: If set to true, attempt to discard all animated tags.
+                       Enabling this may severly mangle complex subtitles and
+                       should only be considered as an last ditch effort of uncertain success
+                       for hardware otherwise incapable of displaing anything.
+                       Will not reliably work with manually edited or allocated events.
+                       (Default: `false` - do nothing)
 
 ### Rendering Modes
 #### JS Blending

src/SubtitleOctopus.cpp

@@ -228,6 +228,8 @@ class SubtitleOctopus {
 private:
     ReusableBuffer2D m_blend;
     RenderBlendResult m_blendResult;
+    bool drop_animations;
+    int scanned_events; // next unscanned event index
 public:
     ASS_Library* ass_library;
     ASS_Renderer* ass_renderer;
@@ -245,12 +247,34 @@ class SubtitleOctopus {
         track = NULL;
         canvas_w = 0;
         canvas_h = 0;
+        drop_animations = false;
+        scanned_events = 0;
     }
 
     void setLogLevel(int level) {
         log_level = level;
     }
 
+    void setDropAnimations(int value) {
+        drop_animations = !!value;
+        if (drop_animations)
+            scanAnimations(scanned_events);
+    }
+
+    /*
+     * \brief Scan events starting at index i for animations
+     * and discard animated tags when found.
+     * Note that once animated tags were dropped they cannot be restored.
+     * Updates the class memeber scanned_events to last scanned index.
+     */
+    void scanAnimations(int i) {
+        ASS_Event *cur = track->events;
+        for (; i < track->n_events; i++) {
+             _is_event_animated(track->events + i, drop_animations);
+        }
+        scanned_events = i;
+    }
+
     void initLibrary(int frame_w, int frame_h) {
         ass_library = ass_library_init();
         if (!ass_library) {
@@ -280,6 +304,7 @@ class SubtitleOctopus {
             fprintf(stderr, "jso: Failed to start a track\n");
             exit(4);
         }
+        scanAnimations(0);
     }
 
     void createTrackMem(char *buf, unsigned long bufsize) {
@@ -289,6 +314,7 @@ class SubtitleOctopus {
             fprintf(stderr, "jso: Failed to start a track\n");
             exit(4);
         }
+        scanAnimations(0);
     }
 
     void removeTrack() {

src/post-worker.js

@@ -8,6 +8,7 @@ self.nextIsRaf = false;
 self.lastCurrentTimeReceivedAt = Date.now();
 self.targetFps = 24;
 self.libassMemoryLimit = 0; // in MiB
+self.dropAllAnimations = false;
 
 self.width = 0;
 self.height = 0;
@@ -565,6 +566,7 @@ function onMessageFromMainEmscriptenThread(message) {
             self.targetFps = message.data.targetFps || self.targetFps;
             self.libassMemoryLimit = message.data.libassMemoryLimit || self.libassMemoryLimit;
             self.libassGlyphLimit = message.data.libassGlyphLimit || 0;
+            self.dropAllAnimations = !!message.data.dropAllAnimations || self.dropAllAnimations;
             removeRunDependency('worker-init');
             postMessage({
                 target: "ready",

src/pre-worker.js

@@ -108,6 +108,7 @@ Module['onRuntimeInitialized'] = function () {
     self.blendH = Module._malloc(4);
 
     self.octObj.initLibrary(screen.width, screen.height);
+    self.octObj.setDropAnimations(self.dropAllAnimations);
     self.octObj.createTrack("/sub.ass");
     self.ass_track = self.octObj.track;
     self.ass_library = self.octObj.ass_library;

src/subtitles-octopus.js

@@ -20,6 +20,7 @@ var SubtitlesOctopus = function (options) {
     self.prescaleFactor = options.prescaleFactor || 1.0;
     self.prescaleHeightLimit = options.prescaleHeightLimit || 1080;
     self.maxRenderHeight = options.maxRenderHeight || 0; // 0 - no limit
+    self.dropAllAnimations = options.dropAllAnimations || false; // attempt to remove all animations as a last ditch effort for displaying on weak hardware; may severly mangle subtitles if enabled
     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
@@ -113,7 +114,8 @@ var SubtitlesOctopus = function (options) {
             debug: self.debug,
             targetFps: self.targetFps,
             libassMemoryLimit: self.libassMemoryLimit,
-            libassGlyphLimit: self.libassGlyphLimit
+            libassGlyphLimit: self.libassGlyphLimit,
+            dropAllAnimations: self.dropAllAnimations
         });
     };