Cache trimmed bounds calculation on DocExporter

The cache of the whole sprite trimmed bounds makes sense only in the
UI preview mode.

src/app/doc_exporter.cpp

@@ -561,6 +561,7 @@ DocExporter::DocExporter()
   : m_docBuf(std::make_shared<doc::ImageBuffer>())
   , m_sampleBuf(std::make_shared<doc::ImageBuffer>())
 {
+  m_cache.spriteId = doc::NullId;
   reset();
 }
 
@@ -833,8 +834,23 @@ void DocExporter::captureSamples(Samples& samples,
     }
 
     gfx::Rect spriteBounds = sprite->bounds();
-    if (m_trimSprite)
-      spriteBounds = get_trimmed_bounds(sprite, m_trimByGrid);
+    if (m_trimSprite) {
+      if (m_cache.spriteId == sprite->id() &&
+          m_cache.spriteVer == sprite->version() &&
+          m_cache.trimmedByGrid == m_trimByGrid) {
+        spriteBounds = m_cache.trimmedBounds;
+      }
+      else {
+        spriteBounds = get_trimmed_bounds(sprite, m_trimByGrid);
+
+        // Cache trimmed bounds so we don't have to recalculate them
+        // in the next iteration/preview.
+        m_cache.spriteId = sprite->id();
+        m_cache.spriteVer = sprite->version();
+        m_cache.trimmedByGrid = m_trimByGrid;
+        m_cache.trimmedBounds = spriteBounds;
+      }
+    }
 
     frame_t outputFrame = 0;
     for (frame_t frame : item.getSelectedFrames()) {

src/app/doc_exporter.h

@@ -16,7 +16,9 @@
 #include "doc/frame.h"
 #include "doc/image_buffer.h"
 #include "doc/object_id.h"
+#include "doc/object_version.h"
 #include "gfx/fwd.h"
+#include "gfx/rect.h"
 
 #include <iosfwd>
 #include <map>
@@ -167,6 +169,15 @@ namespace app {
     doc::ImageBufferPtr m_docBuf;
     doc::ImageBufferPtr m_sampleBuf;
 
+    // Trimmed bounds of a specific sprite (to avoid recalculating
+    // this)
+    struct Cache {
+      doc::ObjectId spriteId;
+      doc::ObjectVersion spriteVer;
+      gfx::Rect trimmedBounds;
+      bool trimmedByGrid;
+    } m_cache;
+
     DISABLE_COPYING(DocExporter);
   };
 

src/doc/object.h

@@ -10,11 +10,10 @@
 
 #include "doc/object_id.h"
 #include "doc/object_type.h"
+#include "doc/object_version.h"
 
 namespace doc {
 
-  typedef uint32_t ObjectVersion;
-
   class Object {
   public:
     Object(ObjectType type);

src/doc/object_version.h

@@ -0,0 +1,19 @@
+// Aseprite Document Library
+// Copyright (C) 2019  Igara Studio S.A.
+//
+// This file is released under the terms of the MIT license.
+// Read LICENSE.txt for more information.
+
+#ifndef DOC_OBJECT_VERSION_H_INCLUDED
+#define DOC_OBJECT_VERSION_H_INCLUDED
+#pragma once
+
+#include "base/ints.h"
+
+namespace doc {
+
+  typedef uint32_t ObjectVersion;
+
+} // namespace doc
+
+#endif