From 1fb463f931e8daae02e906c06ae4768cdfd77f7c Mon Sep 17 00:00:00 2001
From: David Capello <davidcapello@gmail.com>
Date: Fri, 16 Mar 2018 11:03:50 -0300
Subject: [PATCH] Add option to export GIF for Twitter (#1220, #1252)

---
 data/pref.xml                      |  1 +
 data/strings/en.ini                |  5 ++++
 data/widgets/export_file.xml       |  2 ++
 src/app/commands/cmd_save_file.cpp |  3 +++
 src/app/file/gif_format.cpp        | 43 +++++++++++++++++++++++++++---
 src/app/file/gif_format.h          | 21 +++++++++++++++
 src/app/ui/export_file_window.cpp  |  7 +++++
 src/app/ui/export_file_window.h    |  1 +
 8 files changed, 79 insertions(+), 4 deletions(-)
 create mode 100644 src/app/file/gif_format.h

diff --git a/data/pref.xml b/data/pref.xml
index 6133b7baf..a6847b35f 100644
--- a/data/pref.xml
+++ b/data/pref.xml
@@ -359,6 +359,7 @@
       <option id="frame_tag" type="std::string" />
       <option id="ani_dir" type="doc::AniDir" default="doc::AniDir::FORWARD" />
       <option id="apply_pixel_ratio" type="bool" default="false" />
+      <option id="for_twitter" type="bool" default="false" />
     </section>
     <section id="sprite_sheet">
       <option id="defined" type="bool" default="false" />
diff --git a/data/strings/en.ini b/data/strings/en.ini
index 3dc537e9e..023b0d408 100644
--- a/data/strings/en.ini
+++ b/data/strings/en.ini
@@ -463,6 +463,11 @@ layers = Layers:
 frames = Frames:
 anidir = Animation Direction:
 pixel_ratio = Apply pixel ratio
+for_twitter = Export for Twitter
+for_twitter_tooltip = <<<END
+Adjust the duration of the last frame to 1/4 so
+Twitter reproduces the animation correctly.
+END
 export = &Export
 cancel = &Cancel
 
diff --git a/data/widgets/export_file.xml b/data/widgets/export_file.xml
index 751649fa8..45702dc84 100644
--- a/data/widgets/export_file.xml
+++ b/data/widgets/export_file.xml
@@ -34,6 +34,8 @@
 
       <check id="pixel_ratio" text="@.pixel_ratio" cell_hspan="3" />
 
+      <check id="for_twitter" text="@.for_twitter" tooltip="@.for_twitter_tooltip" cell_hspan="3" />
+
       <hbox cell_hspan="3">
         <boxfiller />
         <hbox homogeneous="true">
diff --git a/src/app/commands/cmd_save_file.cpp b/src/app/commands/cmd_save_file.cpp
index 1b733353b..513a1f4d5 100644
--- a/src/app/commands/cmd_save_file.cpp
+++ b/src/app/commands/cmd_save_file.cpp
@@ -17,6 +17,7 @@
 #include "app/console.h"
 #include "app/context_access.h"
 #include "app/file/file.h"
+#include "app/file/gif_format.h"
 #include "app/file_selector.h"
 #include "app/i18n/strings.h"
 #include "app/job.h"
@@ -386,6 +387,8 @@ again:;
       case doc::AniDir::PING_PONG: m_aniDir = "ping-pong"; break;
     }
 
+    GifEncoderDurationFix fix(win.isForTwitter());
+
     saveDocumentInBackground(
       context, doc, outputFilename, false);
 
diff --git a/src/app/file/gif_format.cpp b/src/app/file/gif_format.cpp
index d0f8f0e4a..d796bf86d 100644
--- a/src/app/file/gif_format.cpp
+++ b/src/app/file/gif_format.cpp
@@ -14,6 +14,7 @@
 #include "app/file/file.h"
 #include "app/file/file_format.h"
 #include "app/file/format_options.h"
+#include "app/file/gif_format.h"
 #include "app/file/gif_options.h"
 #include "app/modules/gui.h"
 #include "app/pref/preferences.h"
@@ -102,6 +103,21 @@ FileFormat* CreateGifFormat()
 static int interlaced_offset[] = { 0, 4, 2, 1 };
 static int interlaced_jumps[] = { 8, 8, 4, 2 };
 
+// True if the GifEncoder should save the animation for Twitter:
+// * Frames duration >= 2, and
+// * Last frame 1/4 of its duration
+static bool fix_last_frame_duration = false;
+
+GifEncoderDurationFix::GifEncoderDurationFix(bool state)
+{
+  fix_last_frame_duration = state;
+}
+
+GifEncoderDurationFix::~GifEncoderDurationFix()
+{
+  fix_last_frame_duration = false;
+}
+
 struct GifFilePtr {
 public:
 #if GIFLIB_MAJOR >= 5
@@ -967,7 +983,9 @@ public:
       if (frameBounds.isEmpty())
         frameBounds = gfx::Rect(0, 0, 1, 1);
 
-      writeImage(gifFrame, frame, frameBounds, disposal);
+      writeImage(gifFrame, frame, frameBounds, disposal,
+                 // Only the last frame in the animation needs the fix
+                 (fix_last_frame_duration && gifFrame == nframes-1));
 
       // Dispose/clear frame content
       process_disposal_method(m_previousImage,
@@ -1035,10 +1053,22 @@ private:
 
   // Writes graphics extension record (to save the duration of the
   // frame and maybe the transparency index).
-  void writeExtension(gifframe_t gifFrame, frame_t frame, int transparentIndex, DisposalMethod disposalMethod) {
+  void writeExtension(const gifframe_t gifFrame,
+                      const frame_t frame,
+                      const int transparentIndex,
+                      const DisposalMethod disposalMethod,
+                      const bool fixDuration) {
     unsigned char extension_bytes[5];
     int frameDelay = m_sprite->frameDuration(frame) / 10;
 
+    // Fix duration for Twitter. It looks like the last frame must be
+    // 1/4 of its duration for some strange reason in the Twitter
+    // conversion from GIF to video.
+    if (fixDuration)
+      frameDelay = MAX(2, frameDelay/4);
+    if (fix_last_frame_duration)
+      frameDelay = MAX(2, frameDelay);
+
     extension_bytes[0] = (((int(disposalMethod) & 7) << 2) |
                           (transparentIndex >= 0 ? 1: 0));
     extension_bytes[1] = (frameDelay & 0xff);
@@ -1106,7 +1136,11 @@ private:
     }
   }
 
-  void writeImage(gifframe_t gifFrame, frame_t frame, const gfx::Rect& frameBounds, DisposalMethod disposal) {
+  void writeImage(const gifframe_t gifFrame,
+                  const frame_t frame,
+                  const gfx::Rect& frameBounds,
+                  const DisposalMethod disposal,
+                  const bool fixDuration) {
     UniquePtr<Palette> framePaletteRef;
     UniquePtr<RgbMap> rgbmapRef;
     Palette* framePalette = m_sprite->palette(frame);
@@ -1227,7 +1261,8 @@ private:
       remap.map(m_transparentIndex, localTransparent);
 
     // Write extension record.
-    writeExtension(gifFrame, frame, localTransparent, disposal);
+    writeExtension(gifFrame, frame, localTransparent,
+                   disposal, fixDuration);
 
     // Write the image record.
     if (EGifPutImageDesc(m_gifFile,
diff --git a/src/app/file/gif_format.h b/src/app/file/gif_format.h
new file mode 100644
index 000000000..91cb0d15d
--- /dev/null
+++ b/src/app/file/gif_format.h
@@ -0,0 +1,21 @@
+// Aseprite
+// Copyright (C) 2018  David Capello
+//
+// This program is distributed under the terms of
+// the End-User License Agreement for Aseprite.
+
+#ifndef APP_FILE_GIF_FORMAT_H_INCLUDED
+#define APP_FILE_GIF_FORMAT_H_INCLUDED
+#pragma once
+
+namespace app {
+
+  class GifEncoderDurationFix {
+  public:
+    GifEncoderDurationFix(bool state);
+    ~GifEncoderDurationFix();
+  };
+
+} // namespace app
+
+#endif
diff --git a/src/app/ui/export_file_window.cpp b/src/app/ui/export_file_window.cpp
index 310058fbf..0d90ffb6b 100644
--- a/src/app/ui/export_file_window.cpp
+++ b/src/app/ui/export_file_window.cpp
@@ -49,6 +49,7 @@ ExportFileWindow::ExportFileWindow(const Document* doc)
   fill_frames_combobox(m_doc->sprite(), frames(), m_docPref.saveCopy.frameTag());
   fill_anidir_combobox(anidir(), m_docPref.saveCopy.aniDir());
   pixelRatio()->setSelected(m_docPref.saveCopy.applyPixelRatio());
+  forTwitter()->setSelected(m_docPref.saveCopy.forTwitter());
 
   updateAniDir();
 
@@ -83,6 +84,7 @@ void ExportFileWindow::savePref()
   m_docPref.saveCopy.layer(layersValue());
   m_docPref.saveCopy.frameTag(framesValue());
   m_docPref.saveCopy.applyPixelRatio(applyPixelRatio());
+  m_docPref.saveCopy.forTwitter(isForTwitter());
 }
 
 std::string ExportFileWindow::outputFilenameValue() const
@@ -116,6 +118,11 @@ bool ExportFileWindow::applyPixelRatio() const
   return pixelRatio()->isSelected();
 }
 
+bool ExportFileWindow::isForTwitter() const
+{
+  return forTwitter()->isSelected();
+}
+
 void ExportFileWindow::setOutputFilename(const std::string& pathAndFilename)
 {
   m_outputPath = base::get_file_path(pathAndFilename);
diff --git a/src/app/ui/export_file_window.h b/src/app/ui/export_file_window.h
index 1d47afc9b..3ce0e05a2 100644
--- a/src/app/ui/export_file_window.h
+++ b/src/app/ui/export_file_window.h
@@ -31,6 +31,7 @@ namespace app {
     std::string framesValue() const;
     doc::AniDir aniDirValue() const;
     bool applyPixelRatio() const;
+    bool isForTwitter() const;
 
     obs::signal<std::string()> SelectOutputFile;