Speed up GIF animations

* src/image.c (anim_prune_animation_cache): Tweak the destructor
API.
(gif_destroy): New function.
(gif_load): Use a cache to avoid quadratic CPU usage for animated
images (bug#45224).
(webp_destroy): New function.
(webp_load): Use it.

1 files changed, 179 insertions, 111 deletions

diff --git a/src/image.c b/src/image.c
index a3c98684261..967263e2c60 100644
--- a/src/image.c
+++ b/src/image.c
@@ -8484,7 +8484,7 @@ anim_prune_animation_cache (void)
       else
         {
           if (cache->handle)
-            cache->destructor (cache->handle);
+            cache->destructor (cache);
           if (cache->temp)
             xfree (cache->temp);
           *pcache = cache->next;
@@ -8754,127 +8754,187 @@ static const int interlace_increment[] = {8, 8, 4, 2};
 
 #define GIF_LOCAL_DESCRIPTOR_EXTENSION 249
 
+static void
+gif_destroy (struct anim_cache* cache)
+{
+  int gif_err;
+  gif_close (cache->handle, &gif_err);
+}
+
 static bool
 gif_load (struct frame *f, struct image *img)
 {
   int rc, width, height, x, y, i, j;
   ColorMapObject *gif_color_map;
-  GifFileType *gif;
+  GifFileType *gif = NULL;
   gif_memory_source memsrc;
   Lisp_Object specified_bg = image_spec_value (img->spec, QCbackground, NULL);
   Lisp_Object specified_file = image_spec_value (img->spec, QCfile, NULL);
   Lisp_Object specified_data = image_spec_value (img->spec, QCdata, NULL);
-  EMACS_INT idx;
+  EMACS_INT idx = -1;
   int gif_err;
+  struct anim_cache* cache = NULL;
 
-  if (NILP (specified_data))
+  /* Which sub-image are we to display?  */
+  {
+    Lisp_Object image_number = image_spec_value (img->spec, QCindex, NULL);
+    idx = FIXNUMP (image_number) ? XFIXNAT (image_number) : 0;
+  }
+
+  if (idx != -1)
     {
-      Lisp_Object file = image_find_image_file (specified_file);
-      if (!STRINGP (file))
+      /* If this is an animated image, create a cache for it.  */
+      cache = anim_get_animation_cache (img->spec);
+      if (cache->handle)
         {
-          image_error ("Cannot find image file `%s'", specified_file);
-          return false;
+          /* We have an old cache entry, and it looks correct, so use
+             it.  */
+          if (cache->index == idx - 1)
+            gif = cache->handle;
         }
+    }
 
-      Lisp_Object encoded_file = ENCODE_FILE (file);
+  /* If we don't have a cached entry, read the image.  */
+  if (! gif)
+    {
+      if (NILP (specified_data))
+        {
+          Lisp_Object file = image_find_image_file (specified_file);
+          if (!STRINGP (file))
+            {
+              image_error ("Cannot find image file `%s'", specified_file);
+              return false;
+            }
+
+          Lisp_Object encoded_file = ENCODE_FILE (file);
 #ifdef WINDOWSNT
-      encoded_file = ansi_encode_filename (encoded_file);
+          encoded_file = ansi_encode_filename (encoded_file);
 #endif
 
-      /* Open the GIF file.  */
+          /* Open the GIF file.  */
 #if GIFLIB_MAJOR < 5
-      gif = DGifOpenFileName (SSDATA (encoded_file));
+          gif = DGifOpenFileName (SSDATA (encoded_file));
 #else
-      gif = DGifOpenFileName (SSDATA (encoded_file), &gif_err);
+          gif = DGifOpenFileName (SSDATA (encoded_file), &gif_err);
 #endif
-      if (gif == NULL)
-        {
+          if (gif == NULL)
+            {
 #if HAVE_GIFERRORSTRING
-          const char *errstr = GifErrorString (gif_err);
-          if (errstr)
-            image_error ("Cannot open `%s': %s", file, build_string (errstr));
-          else
+              const char *errstr = GifErrorString (gif_err);
+              if (errstr)
+                image_error ("Cannot open `%s': %s", file,
+                             build_string (errstr));
+              else
 #endif
-          image_error ("Cannot open `%s'", file);
-          return false;
+                image_error ("Cannot open `%s'", file);
+              return false;
+            }
         }
-    }
-  else
-    {
-      if (!STRINGP (specified_data))
+      else
         {
-          image_error ("Invalid image data `%s'", specified_data);
-          return false;
-        }
+          if (!STRINGP (specified_data))
+            {
+              image_error ("Invalid image data `%s'", specified_data);
+              return false;
+            }
 
-      /* Read from memory! */
-      current_gif_memory_src = &memsrc;
-      memsrc.bytes = SDATA (specified_data);
-      memsrc.len = SBYTES (specified_data);
-      memsrc.index = 0;
+          /* Read from memory! */
+          current_gif_memory_src = &memsrc;
+          memsrc.bytes = SDATA (specified_data);
+          memsrc.len = SBYTES (specified_data);
+          memsrc.index = 0;
 
 #if GIFLIB_MAJOR < 5
-      gif = DGifOpen (&memsrc, gif_read_from_memory);
+          gif = DGifOpen (&memsrc, gif_read_from_memory);
 #else
-      gif = DGifOpen (&memsrc, gif_read_from_memory, &gif_err);
+          gif = DGifOpen (&memsrc, gif_read_from_memory, &gif_err);
+#endif
+          if (!gif)
+            {
+#if HAVE_GIFERRORSTRING
+              const char *errstr = GifErrorString (gif_err);
+              if (errstr)
+                image_error ("Cannot open memory source `%s': %s",
+                             img->spec, build_string (errstr));
+              else
 #endif
-      if (!gif)
+                image_error ("Cannot open memory source `%s'", img->spec);
+              return false;
+            }
+        }
+
+      /* Before reading entire contents, check the declared image size. */
+      if (!check_image_size (f, gif->SWidth, gif->SHeight))
+        {
+          image_size_error ();
+          goto gif_error;
+        }
+
+      /* Read entire contents.  */
+      rc = DGifSlurp (gif);
+      if (rc == GIF_ERROR || gif->ImageCount <= 0)
         {
 #if HAVE_GIFERRORSTRING
-          const char *errstr = GifErrorString (gif_err);
+          const char *errstr = GifErrorString (gif->Error);
           if (errstr)
-            image_error ("Cannot open memory source `%s': %s",
-                         img->spec, build_string (errstr));
+            if (NILP (specified_data))
+              image_error ("Error reading `%s' (%s)", img->spec,
+                           build_string (errstr));
+            else
+              image_error ("Error reading GIF data: %s",
+                           build_string (errstr));
           else
 #endif
-          image_error ("Cannot open memory source `%s'", img->spec);
-          return false;
+            if (NILP (specified_data))
+              image_error ("Error reading `%s'", img->spec);
+            else
+              image_error ("Error reading GIF data");
+          goto gif_error;
         }
-    }
 
-  /* Before reading entire contents, check the declared image size. */
-  if (!check_image_size (f, gif->SWidth, gif->SHeight))
+      width = img->width = gif->SWidth;
+      height = img->height = gif->SHeight;
+
+      /* Check that the selected subimages fit.  It's not clear whether
+         the GIF spec requires this, but Emacs can crash if they don't fit.  */
+      for (j = 0; j <= idx; ++j)
+        {
+          struct SavedImage *subimage = gif->SavedImages + j;
+          int subimg_width = subimage->ImageDesc.Width;
+          int subimg_height = subimage->ImageDesc.Height;
+          int subimg_top = subimage->ImageDesc.Top;
+          int subimg_left = subimage->ImageDesc.Left;
+          if (! (subimg_width >= 0 && subimg_height >= 0
+                 && 0 <= subimg_top && subimg_top <= height - subimg_height
+                 && 0 <= subimg_left && subimg_left <= width - subimg_width))
+            {
+              image_error ("Subimage does not fit in image");
+              goto gif_error;
+            }
+        }
+    }
+  else
     {
-      image_size_error ();
-      goto gif_error;
+      /* Cached image; set data.  */
+      width = img->width = gif->SWidth;
+      height = img->height = gif->SHeight;
     }
 
-  /* Read entire contents.  */
-  rc = DGifSlurp (gif);
-  if (rc == GIF_ERROR || gif->ImageCount <= 0)
+  if (idx < 0 || idx >= gif->ImageCount)
     {
-#if HAVE_GIFERRORSTRING
-      const char *errstr = GifErrorString (gif->Error);
-      if (errstr)
-        if (NILP (specified_data))
-          image_error ("Error reading `%s' (%s)", img->spec,
-                       build_string (errstr));
-        else
-          image_error ("Error reading GIF data: %s",
-                       build_string (errstr));
-      else
-#endif
-        if (NILP (specified_data))
-          image_error ("Error reading `%s'", img->spec);
-        else
-          image_error ("Error reading GIF data");
+      image_error ("Invalid image number `%s' in image `%s'",
+                   make_fixnum (idx), img->spec);
       goto gif_error;
     }
 
-  /* Which sub-image are we to display?  */
-  {
-    Lisp_Object image_number = image_spec_value (img->spec, QCindex, NULL);
-    idx = FIXNUMP (image_number) ? XFIXNAT (image_number) : 0;
-    if (idx < 0 || idx >= gif->ImageCount)
-      {
-        image_error ("Invalid image number `%s' in image `%s'",
-                     image_number, img->spec);
-        goto gif_error;
-      }
-  }
-
-  width = img->width = gif->SWidth;
-  height = img->height = gif->SHeight;
+  /* It's an animated image, so initalize the cache.  */
+  if (cache && !cache->handle)
+    {
+      cache->handle = gif;
+      cache->destructor = (void (*)(void *)) &gif_destroy;
+      cache->width = width;
+      cache->height = height;
+    }
 
   img->corners[TOP_CORNER] = gif->SavedImages[0].ImageDesc.Top;
   img->corners[LEFT_CORNER] = gif->SavedImages[0].ImageDesc.Left;
@@ -8889,24 +8949,6 @@ gif_load (struct frame *f, struct image *img)
       goto gif_error;
     }
 
-  /* Check that the selected subimages fit.  It's not clear whether
-     the GIF spec requires this, but Emacs can crash if they don't fit.  */
-  for (j = 0; j <= idx; ++j)
-    {
-      struct SavedImage *subimage = gif->SavedImages + j;
-      int subimg_width = subimage->ImageDesc.Width;
-      int subimg_height = subimage->ImageDesc.Height;
-      int subimg_top = subimage->ImageDesc.Top;
-      int subimg_left = subimage->ImageDesc.Left;
-      if (! (subimg_width >= 0 && subimg_height >= 0
-             && 0 <= subimg_top && subimg_top <= height - subimg_height
-             && 0 <= subimg_left && subimg_left <= width - subimg_width))
-        {
-          image_error ("Subimage does not fit in image");
-          goto gif_error;
-        }
-    }
-
   /* Create the X image and pixmap.  */
   Emacs_Pix_Container ximg;
   if (!image_create_x_image_and_pixmap (f, img, width, height, 0, &ximg, 0))
@@ -8944,11 +8986,6 @@ gif_load (struct frame *f, struct image *img)
 
   /* Read the GIF image into the X image.   */
 
-  /* FIXME: With the current implementation, loading an animated gif
-     is quadratic in the number of animation frames, since each frame
-     is a separate struct image.  We must provide a way for a single
-     gif_load call to construct and save all animation frames.  */
-
   init_color_table ();
 
   unsigned long bgcolor UNINIT;
@@ -8963,7 +9000,19 @@ gif_load (struct frame *f, struct image *img)
 #endif
     }
 
-  for (j = 0; j <= idx; ++j)
+  int start_frame = 0;
+
+  /* We have animation data in the cache, so copy it over so that we
+     can alter it.  */
+  int cache_image_size = width * height * ximg->bits_per_pixel / 8;
+  if (cache && cache->temp)
+    {
+      memcpy (ximg->data, cache->temp, cache_image_size);
+      start_frame = cache->index;
+      cache->index = idx;
+    }
+
+  for (j = start_frame; j <= idx; ++j)
     {
       /* We use a local variable `raster' here because RasterBits is a
          char *, which invites problems with bytes >= 0x80.  */
@@ -9074,6 +9123,15 @@ gif_load (struct frame *f, struct image *img)
         }
     }
 
+  if (cache)
+    {
+      /* Allocate an area to store what we have computed so far.  */
+      if (! cache->temp)
+        cache->temp = xmalloc (cache_image_size);
+      /* Copy over the data to the cache.  */
+      memcpy (cache->temp, ximg->data, cache_image_size);
+    }
+
 #ifdef COLOR_TABLE_SUPPORT
   img->colors = colors_in_color_table (&img->ncolors);
   free_color_table ();
@@ -9114,17 +9172,20 @@ gif_load (struct frame *f, struct image *img)
                             Fcons (make_fixnum (gif->ImageCount),
                                    img->lisp_data));
 
-  if (gif_close (gif, &gif_err) == GIF_ERROR)
+  if (!cache)
     {
+      if (gif_close (gif, &gif_err) == GIF_ERROR)
+        {
 #if HAVE_GIFERRORSTRING
-      char const *error_text = GifErrorString (gif_err);
+          char const *error_text = GifErrorString (gif_err);
 
-      if (error_text)
-        image_error ("Error closing `%s': %s",
-                     img->spec, build_string (error_text));
-      else
+          if (error_text)
+            image_error ("Error closing `%s': %s",
+                         img->spec, build_string (error_text));
+          else
 #endif
-      image_error ("Error closing `%s'", img->spec);
+            image_error ("Error closing `%s'", img->spec);
+        }
     }
 
   /* Maybe fill in the background field while we have ximg handy. */
@@ -9138,7 +9199,8 @@ gif_load (struct frame *f, struct image *img)
   return true;
 
  gif_error:
-  gif_close (gif, NULL);
+  if (!cache)
+    gif_close (gif, NULL);
   return false;
 }
 
@@ -9292,6 +9354,12 @@ init_webp_functions (void)
 
 #endif /* WINDOWSNT */
 
+static void
+webp_destroy (struct anim_cache* cache)
+{
+  WebPAnimDecoderDelete (cache->handle);
+}
+
 /* Load WebP image IMG for use on frame F.  Value is true if
    successful.  */
 
@@ -9408,7 +9476,7 @@ webp_load (struct frame *f, struct image *img)
           cache->height = height = WebPDemuxGetI (demux,
                                                   WEBP_FF_CANVAS_HEIGHT);
           cache->frames = frames = WebPDemuxGetI (demux, WEBP_FF_FRAME_COUNT);
-          cache->destructor = (void (*)(void *)) &WebPAnimDecoderDelete;
+          cache->destructor = (void (*)(void *)) webp_destroy;
           WebPDemuxDelete (demux);
 
           WebPAnimDecoderOptions dec_options;