Add support for saving animated icons

Add support for exporting animated DSi icons as GIF using the
header-only gif.h library.

6 files changed, 942 insertions, 29 deletions

diff --git a/src/frontend/qt_sdl/ROMInfoDialog.cpp b/src/frontend/qt_sdl/ROMInfoDialog.cpp
index b381803..34917d0 100644
--- a/src/frontend/qt_sdl/ROMInfoDialog.cpp
+++ b/src/frontend/qt_sdl/ROMInfoDialog.cpp
@@ -21,6 +21,8 @@
 

 #include <QFileDialog>

 

+#include "gif-h/gif.h"

+

 #include "NDS.h"

 #include "NDSCart.h"

 #include "Platform.h"

@@ -45,23 +47,24 @@ ROMInfoDialog::ROMInfoDialog(QWidget* parent) : QDialog(parent), ui(new Ui::ROMI
 

     const NDSBanner* banner = NDS::NDSCartSlot->GetCart()->Banner();

     const NDSHeader& header = NDS::NDSCartSlot->GetCart()->GetHeader();

+

     u32 iconData[32 * 32];

     ROMManager::ROMIcon(banner->Icon, banner->Palette, iconData);

-    iconImage = QImage(reinterpret_cast<unsigned char*>(iconData), 32, 32, QImage::Format_ARGB32).copy();

+    iconImage = QImage(reinterpret_cast<u8*>(iconData), 32, 32, QImage::Format_RGBA8888).copy();

     ui->iconImage->setPixmap(QPixmap::fromImage(iconImage));

 

     if (banner->Version == 0x103)

     {

-        u32 animatedIconData[32 * 32 * 64] = {0};

+        ui->saveAnimatedIconButton->setEnabled(true);

+

         ROMManager::AnimatedROMIcon(banner->DSiIcon, banner->DSiPalette, banner->DSiSequence, animatedIconData, animatedSequence);

 

-        for (int i = 0; i < 64; i++)

+        for (u32* image: animatedIconData)

         {

-            if (animatedIconData[32 * 32 * i] == 0)

+            if (!image)

                 break;

-            animatedIconImages.push_back(QPixmap::fromImage(QImage(reinterpret_cast<unsigned char*>(&animatedIconData[32 * 32 * i]), 32, 32, QImage::Format_ARGB32).copy()));

+            animatedIconImages.push_back(QPixmap::fromImage(QImage(reinterpret_cast<u8*>(image), 32, 32, QImage::Format_RGBA8888).copy()));

         }

-

         iconTimeline = new QTimeLine(animatedSequence.size() / 60 * 1000, this);

         iconTimeline->setFrameRange(0, animatedSequence.size() - 1);

         iconTimeline->setLoopCount(0);

@@ -139,6 +142,30 @@ void ROMInfoDialog::on_saveIconButton_clicked()
     iconImage.save(filename, "PNG");

 }

 

+void ROMInfoDialog::on_saveAnimatedIconButton_clicked()

+{

+    QString filename = QFileDialog::getSaveFileName(this,

+                                                    "Save Animated Icon",

+                                                    QString::fromStdString(Config::LastROMFolder),

+                                                    "GIF Images (*.gif)");

+    if (filename.isEmpty())

+        return;

+

+

+    GifWriter writer;

+

+    // The GIF format only supports delays of 0.01 seconds, so 0.0166... (60fps)

+    // is rounded up to 0.02 (50fps)

+    GifBegin(&writer, filename.toStdString().c_str(), 32, 32, 2);

+    for (int i: animatedSequence)

+    {

+        if (animatedIconData[i] == 0)

+            break;

+        GifWriteFrame(&writer, reinterpret_cast<u8*>(animatedIconData[i]), 32, 32, 2);

+    }

+    GifEnd(&writer);

+}

+

 void ROMInfoDialog::iconSetFrame(int frame)

 {

     ui->dsiIconImage->setPixmap(animatedIconImages[animatedSequence[frame]]);

diff --git a/src/frontend/qt_sdl/ROMInfoDialog.h b/src/frontend/qt_sdl/ROMInfoDialog.h
index 3963037..630ac22 100644
--- a/src/frontend/qt_sdl/ROMInfoDialog.h
+++ b/src/frontend/qt_sdl/ROMInfoDialog.h
@@ -60,6 +60,7 @@ private slots:
     void done(int r);

 

     void on_saveIconButton_clicked();

+    void on_saveAnimatedIconButton_clicked();

 

     void iconSetFrame(int frame);

 

@@ -68,6 +69,7 @@ private:
 

     QImage iconImage;

     QTimeLine* iconTimeline;

+    u32 animatedIconData[64][32*32] = {0};

     std::vector<QPixmap> animatedIconImages;

     std::vector<int> animatedSequence;

 };

diff --git a/src/frontend/qt_sdl/ROMInfoDialog.ui b/src/frontend/qt_sdl/ROMInfoDialog.ui
index 1c9d844..2559288 100644
--- a/src/frontend/qt_sdl/ROMInfoDialog.ui
+++ b/src/frontend/qt_sdl/ROMInfoDialog.ui
@@ -6,8 +6,8 @@
    <rect>
     <x>0</x>
     <y>0</y>
-    <width>559</width>
-    <height>532</height>
+    <width>557</width>
+    <height>547</height>
    </rect>
   </property>
   <property name="sizePolicy">
@@ -525,10 +525,17 @@
    <item row="0" column="0" colspan="2">
     <widget class="QGroupBox" name="groupBox_2">
      <layout class="QGridLayout" name="gridLayout_9">
+      <item row="1" column="1">
+       <widget class="QPushButton" name="saveIconButton">
+        <property name="text">
+         <string>Save icon</string>
+        </property>
+       </widget>
+      </item>
       <item row="0" column="1">
        <widget class="QGroupBox" name="iconBox">
         <property name="sizePolicy">
-         <sizepolicy hsizetype="Preferred" vsizetype="Preferred">
+         <sizepolicy hsizetype="Preferred" vsizetype="Fixed">
           <horstretch>0</horstretch>
           <verstretch>0</verstretch>
          </sizepolicy>
@@ -619,7 +626,7 @@
             <property name="bottomMargin">
              <number>1</number>
             </property>
-            <item row="0" column="0">
+            <item row="0" column="1">
              <widget class="QLabel" name="iconTitle">
               <property name="sizePolicy">
                <sizepolicy hsizetype="MinimumExpanding" vsizetype="MinimumExpanding">
@@ -644,16 +651,42 @@
               </property>
              </widget>
             </item>
+            <item row="0" column="2">
+             <spacer name="horizontalSpacer_2">
+              <property name="orientation">
+               <enum>Qt::Horizontal</enum>
+              </property>
+              <property name="sizeHint" stdset="0">
+               <size>
+                <width>20</width>
+                <height>20</height>
+               </size>
+              </property>
+             </spacer>
+            </item>
+            <item row="0" column="0">
+             <spacer name="horizontalSpacer_4">
+              <property name="orientation">
+               <enum>Qt::Horizontal</enum>
+              </property>
+              <property name="sizeHint" stdset="0">
+               <size>
+                <width>20</width>
+                <height>20</height>
+               </size>
+              </property>
+             </spacer>
+            </item>
            </layout>
           </widget>
          </item>
         </layout>
        </widget>
       </item>
-      <item row="0" column="2">
+      <item row="0" column="2" alignment="Qt::AlignHCenter">
        <widget class="QGroupBox" name="dsiIconBox">
         <property name="sizePolicy">
-         <sizepolicy hsizetype="Minimum" vsizetype="Minimum">
+         <sizepolicy hsizetype="Fixed" vsizetype="Fixed">
           <horstretch>0</horstretch>
           <verstretch>0</verstretch>
          </sizepolicy>
@@ -724,25 +757,40 @@
         </layout>
        </widget>
       </item>
-      <item row="0" column="3">
+      <item row="1" column="2">
+       <widget class="QPushButton" name="saveAnimatedIconButton">
+        <property name="enabled">
+         <bool>false</bool>
+        </property>
+        <property name="text">
+         <string>Save animated icon</string>
+        </property>
+       </widget>
+      </item>
+      <item row="0" column="3" rowspan="2">
        <spacer name="horizontalSpacer_3">
         <property name="orientation">
          <enum>Qt::Horizontal</enum>
         </property>
-       </spacer>
-      </item>
-      <item row="1" column="1">
-       <widget class="QPushButton" name="saveIconButton">
-        <property name="text">
-         <string>Save icon</string>
+        <property name="sizeHint" stdset="0">
+         <size>
+          <width>0</width>
+          <height>0</height>
+         </size>
         </property>
-       </widget>
+       </spacer>
       </item>
-      <item row="0" column="0">
+      <item row="0" column="0" rowspan="2">
        <spacer name="horizontalSpacer">
         <property name="orientation">
          <enum>Qt::Horizontal</enum>
         </property>
+        <property name="sizeHint" stdset="0">
+         <size>
+          <width>0</width>
+          <height>0</height>
+         </size>
+        </property>
        </spacer>
       </item>
      </layout>
diff --git a/src/frontend/qt_sdl/ROMManager.cpp b/src/frontend/qt_sdl/ROMManager.cpp
index 0bb6b7f..1c58055 100644
--- a/src/frontend/qt_sdl/ROMManager.cpp
+++ b/src/frontend/qt_sdl/ROMManager.cpp
@@ -1478,7 +1478,7 @@ QString GBACartLabel()
 }
 
 
-void ROMIcon(const u8 (&data)[512], const u16 (&palette)[16], u32* iconRef)
+void ROMIcon(const u8 (&data)[512], const u16 (&palette)[16], u32 (&iconRef)[32*32])
 {
     int index = 0;
     for (int i = 0; i < 4; i++)
@@ -1495,7 +1495,7 @@ void ROMIcon(const u8 (&data)[512], const u16 (&palette)[16], u32* iconRef)
                     u8 b = ((palette[pal_index] >> 10) & 0x1F) * 255 / 31;
                     u8 a = pal_index ? 255: 0;
                     u32* row = &iconRef[256 * i + 32 * k + 8 * j];
-                    row[l] = (a << 24) | (r << 16) | (g << 8) | b;
+                    row[l] = r | (g << 8) | (b << 16) | (a << 24);
                     index++;
                 }
             }
@@ -1509,14 +1509,15 @@ void ROMIcon(const u8 (&data)[512], const u16 (&palette)[16], u32* iconRef)
 #define SEQ_BMP(i) ((i & 0b0000011100000000) >> 8)
 #define SEQ_DUR(i) ((i & 0b0000000011111111) >> 0)
 
-void AnimatedROMIcon(const u8 (&data)[8][512], const u16 (&palette)[8][16], const u16 (&sequence)[64], u32 (&animatedTexRef)[32 * 32 * 64], std::vector<int> &animatedSequenceRef)
+void AnimatedROMIcon(const u8 (&data)[8][512], const u16 (&palette)[8][16], const u16 (&sequence)[64], u32 (&animatedIconRef)[64][32*32], std::vector<int> &animatedSequenceRef)
 {
     for (int i = 0; i < 64; i++)
     {
         if (!sequence[i])
             break;
-        u32* frame = &animatedTexRef[32 * 32 * i];
-        ROMIcon(data[SEQ_BMP(sequence[i])], palette[SEQ_PAL(sequence[i])], frame);
+
+        ROMIcon(data[SEQ_BMP(sequence[i])], palette[SEQ_PAL(sequence[i])], animatedIconRef[i]);
+        u32* frame = animatedIconRef[i];
 
         if (SEQ_FLIPH(sequence[i]))
         {
diff --git a/src/frontend/qt_sdl/ROMManager.h b/src/frontend/qt_sdl/ROMManager.h
index c4be23b..6d95763 100644
--- a/src/frontend/qt_sdl/ROMManager.h
+++ b/src/frontend/qt_sdl/ROMManager.h
@@ -62,11 +62,10 @@ void UndoStateLoad();
 void EnableCheats(bool enable);
 ARCodeFile* GetCheatFile();
 
-void ROMIcon(const u8 (&data)[512], const u16 (&palette)[16], u32* iconRef);
+void ROMIcon(const u8 (&data)[512], const u16 (&palette)[16], u32 (&iconRef)[32*32]);
 void AnimatedROMIcon(const u8 (&data)[8][512], const u16 (&palette)[8][16],
-                     const u16 (&sequence)[64], u32 (&animatedTexRef)[32 * 32 * 64],
+                     const u16 (&sequence)[64], u32 (&animatedIconRef)[64][32*32],
                      std::vector<int> &animatedSequenceRef);
-
 }
 
 #endif // ROMMANAGER_H
diff --git a/src/frontend/qt_sdl/gif-h/gif.h b/src/frontend/qt_sdl/gif-h/gif.h
new file mode 100644
index 0000000..d89ffc3
--- /dev/null
+++ b/src/frontend/qt_sdl/gif-h/gif.h
@@ -0,0 +1,836 @@
+//
+// gif.h
+// by Charlie Tangora
+// Public domain.
+// Email me : ctangora -at- gmail -dot- com
+//
+// This file offers a simple, very limited way to create animated GIFs directly in code.
+//
+// Those looking for particular cleverness are likely to be disappointed; it's pretty
+// much a straight-ahead implementation of the GIF format with optional Floyd-Steinberg
+// dithering. (It does at least use delta encoding - only the changed portions of each
+// frame are saved.)
+//
+// So resulting files are often quite large. The hope is that it will be handy nonetheless
+// as a quick and easily-integrated way for programs to spit out animations.
+//
+// Only RGBA8 is currently supported as an input format. (The alpha is ignored.)
+//
+// If capturing a buffer with a bottom-left origin (such as OpenGL), define GIF_FLIP_VERT
+// to automatically flip the buffer data when writing the image (the buffer itself is
+// unchanged.
+//
+// USAGE:
+// Create a GifWriter struct. Pass it to GifBegin() to initialize and write the header.
+// Pass subsequent frames to GifWriteFrame().
+// Finally, call GifEnd() to close the file handle and free memory.
+//
+
+#ifndef gif_h
+#define gif_h
+
+#include <stdio.h>   // for FILE*
+#include <string.h>  // for memcpy and bzero
+#include <stdint.h>  // for integer typedefs
+#include <stdbool.h> // for bool macros
+
+// Define these macros to hook into a custom memory allocator.
+// TEMP_MALLOC and TEMP_FREE will only be called in stack fashion - frees in the reverse order of mallocs
+// and any temp memory allocated by a function will be freed before it exits.
+// MALLOC and FREE are used only by GifBegin and GifEnd respectively (to allocate a buffer the size of the image, which
+// is used to find changed pixels for delta-encoding.)
+
+#ifndef GIF_TEMP_MALLOC
+#include <stdlib.h>
+#define GIF_TEMP_MALLOC malloc
+#endif
+
+#ifndef GIF_TEMP_FREE
+#include <stdlib.h>
+#define GIF_TEMP_FREE free
+#endif
+
+#ifndef GIF_MALLOC
+#include <stdlib.h>
+#define GIF_MALLOC malloc
+#endif
+
+#ifndef GIF_FREE
+#include <stdlib.h>
+#define GIF_FREE free
+#endif
+
+const int kGifTransIndex = 0;
+
+typedef struct
+{
+    int bitDepth;
+
+    uint8_t r[256];
+    uint8_t g[256];
+    uint8_t b[256];
+
+    // k-d tree over RGB space, organized in heap fashion
+    // i.e. left child of node i is node i*2, right child is node i*2+1
+    // nodes 256-511 are implicitly the leaves, containing a color
+    uint8_t treeSplitElt[256];
+    uint8_t treeSplit[256];
+} GifPalette;
+
+// max, min, and abs functions
+int GifIMax(int l, int r) { return l>r?l:r; }
+int GifIMin(int l, int r) { return l<r?l:r; }
+int GifIAbs(int i) { return i<0?-i:i; }
+
+// walks the k-d tree to pick the palette entry for a desired color.
+// Takes as in/out parameters the current best color and its error -
+// only changes them if it finds a better color in its subtree.
+// this is the major hotspot in the code at the moment.
+void GifGetClosestPaletteColor( GifPalette* pPal, int r, int g, int b, int* bestInd, int* bestDiff, int treeRoot )
+{
+    // base case, reached the bottom of the tree
+    if(treeRoot > (1<<pPal->bitDepth)-1)
+    {
+        int ind = treeRoot-(1<<pPal->bitDepth);
+        if(ind == kGifTransIndex) return;
+
+        // check whether this color is better than the current winner
+        int r_err = r - ((int32_t)pPal->r[ind]);
+        int g_err = g - ((int32_t)pPal->g[ind]);
+        int b_err = b - ((int32_t)pPal->b[ind]);
+        int diff = GifIAbs(r_err)+GifIAbs(g_err)+GifIAbs(b_err);
+
+        if(diff < *bestDiff)
+        {
+            *bestInd = ind;
+            *bestDiff = diff;
+        }
+
+        return;
+    }
+
+    // take the appropriate color (r, g, or b) for this node of the k-d tree
+    int comps[3]; comps[0] = r; comps[1] = g; comps[2] = b;
+    int splitComp = comps[pPal->treeSplitElt[treeRoot]];
+
+    int splitPos = pPal->treeSplit[treeRoot];
+    if(splitPos > splitComp)
+    {
+        // check the left subtree
+        GifGetClosestPaletteColor(pPal, r, g, b, bestInd, bestDiff, treeRoot*2);
+        if( *bestDiff > splitPos - splitComp )
+        {
+            // cannot prove there's not a better value in the right subtree, check that too
+            GifGetClosestPaletteColor(pPal, r, g, b, bestInd, bestDiff, treeRoot*2+1);
+        }
+    }
+    else
+    {
+        GifGetClosestPaletteColor(pPal, r, g, b, bestInd, bestDiff, treeRoot*2+1);
+        if( *bestDiff > splitComp - splitPos )
+        {
+            GifGetClosestPaletteColor(pPal, r, g, b, bestInd, bestDiff, treeRoot*2);
+        }
+    }
+}
+
+void GifSwapPixels(uint8_t* image, int pixA, int pixB)
+{
+    uint8_t rA = image[pixA*4];
+    uint8_t gA = image[pixA*4+1];
+    uint8_t bA = image[pixA*4+2];
+    uint8_t aA = image[pixA*4+3];
+
+    uint8_t rB = image[pixB*4];
+    uint8_t gB = image[pixB*4+1];
+    uint8_t bB = image[pixB*4+2];
+    uint8_t aB = image[pixA*4+3];
+
+    image[pixA*4] = rB;
+    image[pixA*4+1] = gB;
+    image[pixA*4+2] = bB;
+    image[pixA*4+3] = aB;
+
+    image[pixB*4] = rA;
+    image[pixB*4+1] = gA;
+    image[pixB*4+2] = bA;
+    image[pixB*4+3] = aA;
+}
+
+// just the partition operation from quicksort
+int GifPartition(uint8_t* image, const int left, const int right, const int elt, int pivotIndex)
+{
+    const int pivotValue = image[(pivotIndex)*4+elt];
+    GifSwapPixels(image, pivotIndex, right-1);
+    int storeIndex = left;
+    bool split = 0;
+    for(int ii=left; ii<right-1; ++ii)
+    {
+        int arrayVal = image[ii*4+elt];
+        if( arrayVal < pivotValue )
+        {
+            GifSwapPixels(image, ii, storeIndex);
+            ++storeIndex;
+        }
+        else if( arrayVal == pivotValue )
+        {
+            if(split)
+            {
+                GifSwapPixels(image, ii, storeIndex);
+                ++storeIndex;
+            }
+            split = !split;
+        }
+    }
+    GifSwapPixels(image, storeIndex, right-1);
+    return storeIndex;
+}
+
+// Perform an incomplete sort, finding all elements above and below the desired median
+void GifPartitionByMedian(uint8_t* image, int left, int right, int com, int neededCenter)
+{
+    if(left < right-1)
+    {
+        int pivotIndex = left + (right-left)/2;
+
+        pivotIndex = GifPartition(image, left, right, com, pivotIndex);
+
+        // Only "sort" the section of the array that contains the median
+        if(pivotIndex > neededCenter)
+            GifPartitionByMedian(image, left, pivotIndex, com, neededCenter);
+
+        if(pivotIndex < neededCenter)
+            GifPartitionByMedian(image, pivotIndex+1, right, com, neededCenter);
+    }
+}
+
+// Builds a palette by creating a balanced k-d tree of all pixels in the image
+void GifSplitPalette(uint8_t* image, int numPixels, int firstElt, int lastElt, int splitElt, int splitDist, int treeNode, bool buildForDither, GifPalette* pal)
+{
+    if(lastElt <= firstElt || numPixels == 0)
+        return;
+
+    // base case, bottom of the tree
+    if(lastElt == firstElt+1)
+    {
+        if(buildForDither)
+        {
+            // Dithering needs at least one color as dark as anything
+            // in the image and at least one brightest color -
+            // otherwise it builds up error and produces strange artifacts
+            if( firstElt == 1 )
+            {
+                // special case: the darkest color in the image
+                uint32_t r=255, g=255, b=255;
+                for(int ii=0; ii<numPixels; ++ii)
+                {
+                    r = (uint32_t)GifIMin((int32_t)r, image[ii * 4 + 0]);
+                    g = (uint32_t)GifIMin((int32_t)g, image[ii * 4 + 1]);
+                    b = (uint32_t)GifIMin((int32_t)b, image[ii * 4 + 2]);
+                }
+
+                pal->r[firstElt] = (uint8_t)r;
+                pal->g[firstElt] = (uint8_t)g;
+                pal->b[firstElt] = (uint8_t)b;
+
+                return;
+            }
+
+            if( firstElt == (1 << pal->bitDepth)-1 )
+            {
+                // special case: the lightest color in the image
+                uint32_t r=0, g=0, b=0;
+                for(int ii=0; ii<numPixels; ++ii)
+                {
+                    r = (uint32_t)GifIMax((int32_t)r, image[ii * 4 + 0]);
+                    g = (uint32_t)GifIMax((int32_t)g, image[ii * 4 + 1]);
+                    b = (uint32_t)GifIMax((int32_t)b, image[ii * 4 + 2]);
+                }
+
+                pal->r[firstElt] = (uint8_t)r;
+                pal->g[firstElt] = (uint8_t)g;
+                pal->b[firstElt] = (uint8_t)b;
+
+                return;
+            }
+        }
+
+        // otherwise, take the average of all colors in this subcube
+        uint64_t r=0, g=0, b=0;
+        for(int ii=0; ii<numPixels; ++ii)
+        {
+            r += image[ii*4+0];
+            g += image[ii*4+1];
+            b += image[ii*4+2];
+        }
+
+        r += (uint64_t)numPixels / 2;  // round to nearest
+        g += (uint64_t)numPixels / 2;
+        b += (uint64_t)numPixels / 2;
+
+        r /= (uint64_t)numPixels;
+        g /= (uint64_t)numPixels;
+        b /= (uint64_t)numPixels;
+
+        pal->r[firstElt] = (uint8_t)r;
+        pal->g[firstElt] = (uint8_t)g;
+        pal->b[firstElt] = (uint8_t)b;
+
+        return;
+    }
+
+    // Find the axis with the largest range
+    int minR = 255, maxR = 0;
+    int minG = 255, maxG = 0;
+    int minB = 255, maxB = 0;
+    for(int ii=0; ii<numPixels; ++ii)
+    {
+        int r = image[ii*4+0];
+        int g = image[ii*4+1];
+        int b = image[ii*4+2];
+
+        if(r > maxR) maxR = r;
+        if(r < minR) minR = r;
+
+        if(g > maxG) maxG = g;
+        if(g < minG) minG = g;
+
+        if(b > maxB) maxB = b;
+        if(b < minB) minB = b;
+    }
+
+    int rRange = maxR - minR;
+    int gRange = maxG - minG;
+    int bRange = maxB - minB;
+
+    // and split along that axis. (incidentally, this means this isn't a "proper" k-d tree but I don't know what else to call it)
+    int splitCom = 1;
+    if(bRange > gRange) splitCom = 2;
+    if(rRange > bRange && rRange > gRange) splitCom = 0;
+
+    int subPixelsA = numPixels * (splitElt - firstElt) / (lastElt - firstElt);
+    int subPixelsB = numPixels-subPixelsA;
+
+    GifPartitionByMedian(image, 0, numPixels, splitCom, subPixelsA);
+
+    pal->treeSplitElt[treeNode] = (uint8_t)splitCom;
+    pal->treeSplit[treeNode] = image[subPixelsA*4+splitCom];
+
+    GifSplitPalette(image,              subPixelsA, firstElt, splitElt, splitElt-splitDist, splitDist/2, treeNode*2,   buildForDither, pal);
+    GifSplitPalette(image+subPixelsA*4, subPixelsB, splitElt, lastElt,  splitElt+splitDist, splitDist/2, treeNode*2+1, buildForDither, pal);
+}
+
+// Finds all pixels that have changed from the previous image and
+// moves them to the fromt of th buffer.
+// This allows us to build a palette optimized for the colors of the
+// changed pixels only.
+int GifPickChangedPixels( const uint8_t* lastFrame, uint8_t* frame, int numPixels )
+{
+    int numChanged = 0;
+    uint8_t* writeIter = frame;
+
+    for (int ii=0; ii<numPixels; ++ii)
+    {
+        if(lastFrame[0] != frame[0] ||
+           lastFrame[1] != frame[1] ||
+           lastFrame[2] != frame[2])
+        {
+            writeIter[0] = frame[0];
+            writeIter[1] = frame[1];
+            writeIter[2] = frame[2];
+            ++numChanged;
+            writeIter += 4;
+        }
+        lastFrame += 4;
+        frame += 4;
+    }
+
+    return numChanged;
+}
+
+// Creates a palette by placing all the image pixels in a k-d tree and then averaging the blocks at the bottom.
+// This is known as the "modified median split" technique
+void GifMakePalette( const uint8_t* lastFrame, const uint8_t* nextFrame, uint32_t width, uint32_t height, int bitDepth, bool buildForDither, GifPalette* pPal )
+{
+    pPal->bitDepth = bitDepth;
+
+    // SplitPalette is destructive (it sorts the pixels by color) so
+    // we must create a copy of the image for it to destroy
+    size_t imageSize = (size_t)(width * height * 4 * sizeof(uint8_t));
+    uint8_t* destroyableImage = (uint8_t*)GIF_TEMP_MALLOC(imageSize);
+    memcpy(destroyableImage, nextFrame, imageSize);
+
+    int numPixels = (int)(width * height);
+    if(lastFrame)
+        numPixels = GifPickChangedPixels(lastFrame, destroyableImage, numPixels);
+
+    const int lastElt = 1 << bitDepth;
+    const int splitElt = lastElt/2;
+    const int splitDist = splitElt/2;
+
+    GifSplitPalette(destroyableImage, numPixels, 1, lastElt, splitElt, splitDist, 1, buildForDither, pPal);
+
+    GIF_TEMP_FREE(destroyableImage);
+
+    // add the bottom node for the transparency index
+    pPal->treeSplit[1 << (bitDepth-1)] = 0;
+    pPal->treeSplitElt[1 << (bitDepth-1)] = 0;
+
+    pPal->r[0] = pPal->g[0] = pPal->b[0] = 0;
+}
+
+// Implements Floyd-Steinberg dithering, writes palette value to alpha
+void GifDitherImage( const uint8_t* lastFrame, const uint8_t* nextFrame, uint8_t* outFrame, uint32_t width, uint32_t height, GifPalette* pPal )
+{
+    int numPixels = (int)(width * height);
+
+    // quantPixels initially holds color*256 for all pixels
+    // The extra 8 bits of precision allow for sub-single-color error values
+    // to be propagated
+    int32_t *quantPixels = (int32_t *)GIF_TEMP_MALLOC(sizeof(int32_t) * (size_t)numPixels * 4);
+
+    for( int ii=0; ii<numPixels*4; ++ii )
+    {
+        uint8_t pix = nextFrame[ii];
+        int32_t pix16 = (int32_t)(pix) * 256;
+        quantPixels[ii] = pix16;
+    }
+
+    for( uint32_t yy=0; yy<height; ++yy )
+    {
+        for( uint32_t xx=0; xx<width; ++xx )
+        {
+            int32_t* nextPix = quantPixels + 4*(yy*width+xx);
+            const uint8_t* lastPix = lastFrame? lastFrame + 4*(yy*width+xx) : NULL;
+
+            // Compute the colors we want (rounding to nearest)
+            int32_t rr = (nextPix[0] + 127) / 256;
+            int32_t gg = (nextPix[1] + 127) / 256;
+            int32_t bb = (nextPix[2] + 127) / 256;
+
+            // if it happens that we want the color from last frame, then just write out
+            // a transparent pixel
+            if( lastFrame &&
+               lastPix[0] == rr &&
+               lastPix[1] == gg &&
+               lastPix[2] == bb )
+            {
+                nextPix[0] = rr;
+                nextPix[1] = gg;
+                nextPix[2] = bb;
+                nextPix[3] = kGifTransIndex;
+                continue;
+            }
+
+            int32_t bestDiff = 1000000;
+            int32_t bestInd = kGifTransIndex;
+
+            // Search the palete
+            GifGetClosestPaletteColor(pPal, rr, gg, bb, &bestInd, &bestDiff, 1);
+
+            // Write the result to the temp buffer
+            int32_t r_err = nextPix[0] - (int32_t)(pPal->r[bestInd]) * 256;
+            int32_t g_err = nextPix[1] - (int32_t)(pPal->g[bestInd]) * 256;
+            int32_t b_err = nextPix[2] - (int32_t)(pPal->b[bestInd]) * 256;
+
+            nextPix[0] = pPal->r[bestInd];
+            nextPix[1] = pPal->g[bestInd];
+            nextPix[2] = pPal->b[bestInd];
+            nextPix[3] = bestInd;
+
+            // Propagate the error to the four adjacent locations
+            // that we haven't touched yet
+            int quantloc_7 = (int)(yy * width + xx + 1);
+            int quantloc_3 = (int)(yy * width + width + xx - 1);
+            int quantloc_5 = (int)(yy * width + width + xx);
+            int quantloc_1 = (int)(yy * width + width + xx + 1);
+
+            if(quantloc_7 < numPixels)
+            {
+                int32_t* pix7 = quantPixels+4*quantloc_7;
+                pix7[0] += GifIMax( -pix7[0], r_err * 7 / 16 );
+                pix7[1] += GifIMax( -pix7[1], g_err * 7 / 16 );
+                pix7[2] += GifIMax( -pix7[2], b_err * 7 / 16 );
+            }
+
+            if(quantloc_3 < numPixels)
+            {
+                int32_t* pix3 = quantPixels+4*quantloc_3;
+                pix3[0] += GifIMax( -pix3[0], r_err * 3 / 16 );
+                pix3[1] += GifIMax( -pix3[1], g_err * 3 / 16 );
+                pix3[2] += GifIMax( -pix3[2], b_err * 3 / 16 );
+            }
+
+            if(quantloc_5 < numPixels)
+            {
+                int32_t* pix5 = quantPixels+4*quantloc_5;
+                pix5[0] += GifIMax( -pix5[0], r_err * 5 / 16 );
+                pix5[1] += GifIMax( -pix5[1], g_err * 5 / 16 );
+                pix5[2] += GifIMax( -pix5[2], b_err * 5 / 16 );
+            }
+
+            if(quantloc_1 < numPixels)
+            {
+                int32_t* pix1 = quantPixels+4*quantloc_1;
+                pix1[0] += GifIMax( -pix1[0], r_err / 16 );
+                pix1[1] += GifIMax( -pix1[1], g_err / 16 );
+                pix1[2] += GifIMax( -pix1[2], b_err / 16 );
+            }
+        }
+    }
+
+    // Copy the palettized result to the output buffer
+    for( int ii=0; ii<numPixels*4; ++ii )
+    {
+        outFrame[ii] = (uint8_t)quantPixels[ii];
+    }
+
+    GIF_TEMP_FREE(quantPixels);
+}
+
+// Picks palette colors for the image using simple thresholding, no dithering
+void GifThresholdImage( const uint8_t* lastFrame, const uint8_t* nextFrame, uint8_t* outFrame, uint32_t width, uint32_t height, GifPalette* pPal )
+{
+    uint32_t numPixels = width*height;
+    for( uint32_t ii=0; ii<numPixels; ++ii )
+    {
+        // if a previous color is available, and it matches the current color,
+        // set the pixel to transparent
+        if(lastFrame &&
+           lastFrame[0] == nextFrame[0] &&
+           lastFrame[1] == nextFrame[1] &&
+           lastFrame[2] == nextFrame[2])
+        {
+            outFrame[0] = lastFrame[0];
+            outFrame[1] = lastFrame[1];
+            outFrame[2] = lastFrame[2];
+            outFrame[3] = kGifTransIndex;
+        }
+        else
+        {
+            // palettize the pixel
+            int32_t bestDiff = 1000000;
+            int32_t bestInd = 1;
+            GifGetClosestPaletteColor(pPal, nextFrame[0], nextFrame[1], nextFrame[2], &bestInd, &bestDiff, 1);
+
+            // Write the resulting color to the output buffer
+            outFrame[0] = pPal->r[bestInd];
+            outFrame[1] = pPal->g[bestInd];
+            outFrame[2] = pPal->b[bestInd];
+            outFrame[3] = (uint8_t)bestInd;
+        }
+
+        if(lastFrame) lastFrame += 4;
+        outFrame += 4;
+        nextFrame += 4;
+    }
+}
+
+// Simple structure to write out the LZW-compressed portion of the image
+// one bit at a time
+typedef struct
+{
+    uint8_t bitIndex;  // how many bits in the partial byte written so far
+    uint8_t byte;      // current partial byte
+
+    uint32_t chunkIndex;
+    uint8_t chunk[256];   // bytes are written in here until we have 256 of them, then written to the file
+} GifBitStatus;
+
+// insert a single bit
+void GifWriteBit( GifBitStatus* stat, uint32_t bit )
+{
+    bit = bit & 1;
+    bit = bit << stat->bitIndex;
+    stat->byte |= bit;
+
+    ++stat->bitIndex;
+    if( stat->bitIndex > 7 )
+    {
+        // move the newly-finished byte to the chunk buffer
+        stat->chunk[stat->chunkIndex++] = stat->byte;
+        // and start a new byte
+        stat->bitIndex = 0;
+        stat->byte = 0;
+    }
+}
+
+// write all bytes so far to the file
+void GifWriteChunk( FILE* f, GifBitStatus* stat )
+{
+    fputc((int)stat->chunkIndex, f);
+    fwrite(stat->chunk, 1, stat->chunkIndex, f);
+
+    stat->bitIndex = 0;
+    stat->byte = 0;
+    stat->chunkIndex = 0;
+}
+
+void GifWriteCode( FILE* f, GifBitStatus* stat, uint32_t code, uint32_t length )
+{
+    for( uint32_t ii=0; ii<length; ++ii )
+    {
+        GifWriteBit(stat, code);
+        code = code >> 1;
+
+        if( stat->chunkIndex == 255 )
+        {
+            GifWriteChunk(f, stat);
+        }
+    }
+}
+
+// The LZW dictionary is a 256-ary tree constructed as the file is encoded,
+// this is one node
+typedef struct
+{
+    uint16_t m_next[256];
+} GifLzwNode;
+
+// write a 256-color (8-bit) image palette to the file
+void GifWritePalette( const GifPalette* pPal, FILE* f )
+{
+    fputc(0, f);  // first color: transparency
+    fputc(0, f);
+    fputc(0, f);
+
+    for(int ii=1; ii<(1 << pPal->bitDepth); ++ii)
+    {
+        uint32_t r = pPal->r[ii];
+        uint32_t g = pPal->g[ii];
+        uint32_t b = pPal->b[ii];
+
+        fputc((int)r, f);
+        fputc((int)g, f);
+        fputc((int)b, f);
+    }
+}
+
+// write the image header, LZW-compress and write out the image
+void GifWriteLzwImage(FILE* f, uint8_t* image, uint32_t left, uint32_t top,  uint32_t width, uint32_t height, uint32_t delay, GifPalette* pPal)
+{
+    // graphics control extension
+    fputc(0x21, f);
+    fputc(0xf9, f);
+    fputc(0x04, f);
+    fputc(0x05, f); // leave prev frame in place, this frame has transparency
+    fputc(delay & 0xff, f);
+    fputc((delay >> 8) & 0xff, f);
+    fputc(kGifTransIndex, f); // transparent color index
+    fputc(0, f);
+
+    fputc(0x2c, f); // image descriptor block
+
+    fputc(left & 0xff, f);           // corner of image in canvas space
+    fputc((left >> 8) & 0xff, f);
+    fputc(top & 0xff, f);
+    fputc((top >> 8) & 0xff, f);
+
+    fputc(width & 0xff, f);          // width and height of image
+    fputc((width >> 8) & 0xff, f);
+    fputc(height & 0xff, f);
+    fputc((height >> 8) & 0xff, f);
+
+    //fputc(0, f); // no local color table, no transparency
+    //fputc(0x80, f); // no local color table, but transparency
+
+    fputc(0x80 + pPal->bitDepth-1, f); // local color table present, 2 ^ bitDepth entries
+    GifWritePalette(pPal, f);
+
+    const int minCodeSize = pPal->bitDepth;
+    const uint32_t clearCode = 1 << pPal->bitDepth;
+
+    fputc(minCodeSize, f); // min code size 8 bits
+
+    GifLzwNode* codetree = (GifLzwNode*)GIF_TEMP_MALLOC(sizeof(GifLzwNode)*4096);
+
+    memset(codetree, 0, sizeof(GifLzwNode)*4096);
+    int32_t curCode = -1;
+    uint32_t codeSize = (uint32_t)minCodeSize + 1;
+    uint32_t maxCode = clearCode+1;
+
+    GifBitStatus stat;
+    stat.byte = 0;
+    stat.bitIndex = 0;
+    stat.chunkIndex = 0;
+
+    GifWriteCode(f, &stat, clearCode, codeSize);  // start with a fresh LZW dictionary
+
+    for(uint32_t yy=0; yy<height; ++yy)
+    {
+        for(uint32_t xx=0; xx<width; ++xx)
+        {
+    #ifdef GIF_FLIP_VERT
+            // bottom-left origin image (such as an OpenGL capture)
+            uint8_t nextValue = image[((height-1-yy)*width+xx)*4+3];
+    #else
+            // top-left origin
+            uint8_t nextValue = image[(yy*width+xx)*4+3];
+    #endif
+
+            // "loser mode" - no compression, every single code is followed immediately by a clear
+            //WriteCode( f, stat, nextValue, codeSize );
+            //WriteCode( f, stat, 256, codeSize );
+
+            if( curCode < 0 )
+            {
+                // first value in a new run
+                curCode = nextValue;
+            }
+            else if( codetree[curCode].m_next[nextValue] )
+            {
+                // current run already in the dictionary
+                curCode = codetree[curCode].m_next[nextValue];
+            }
+            else
+            {
+                // finish the current run, write a code
+                GifWriteCode(f, &stat, (uint32_t)curCode, codeSize);
+
+                // insert the new run into the dictionary
+                codetree[curCode].m_next[nextValue] = (uint16_t)++maxCode;
+
+                if( maxCode >= (1ul << codeSize) )
+                {
+                    // dictionary entry count has broken a size barrier,
+                    // we need more bits for codes
+                    codeSize++;
+                }
+                if( maxCode == 4095 )
+                {
+                    // the dictionary is full, clear it out and begin anew
+                    GifWriteCode(f, &stat, clearCode, codeSize); // clear tree
+
+                    memset(codetree, 0, sizeof(GifLzwNode)*4096);
+                    codeSize = (uint32_t)(minCodeSize + 1);
+                    maxCode = clearCode+1;
+                }
+
+                curCode = nextValue;
+            }
+        }
+    }
+
+    // compression footer
+    GifWriteCode(f, &stat, (uint32_t)curCode, codeSize);
+    GifWriteCode(f, &stat, clearCode, codeSize);
+    GifWriteCode(f, &stat, clearCode + 1, (uint32_t)minCodeSize + 1);
+
+    // write out the last partial chunk
+    while( stat.bitIndex ) GifWriteBit(&stat, 0);
+    if( stat.chunkIndex ) GifWriteChunk(f, &stat);
+
+    fputc(0, f); // image block terminator
+
+    GIF_TEMP_FREE(codetree);
+}
+
+typedef struct
+{
+    FILE* f;
+    uint8_t* oldImage;
+    bool firstFrame;
+} GifWriter;
+
+// Creates a gif file.
+// The input GIFWriter is assumed to be uninitialized.
+// The delay value is the time between frames in hundredths of a second - note that not all viewers pay much attention to this value.
+bool GifBegin( GifWriter* writer, const char* filename, uint32_t width, uint32_t height, uint32_t delay, int32_t bitDepth = 8, bool dither = false )
+{
+    (void)bitDepth; (void)dither; // Mute "Unused argument" warnings
+#if defined(_MSC_VER) && (_MSC_VER >= 1400)
+	writer->f = 0;
+    fopen_s(&writer->f, filename, "wb");
+#else
+    writer->f = fopen(filename, "wb");
+#endif
+    if(!writer->f) return false;
+
+    writer->firstFrame = true;
+
+    // allocate
+    writer->oldImage = (uint8_t*)GIF_MALLOC(width*height*4);
+
+    fputs("GIF89a", writer->f);
+
+    // screen descriptor
+    fputc(width & 0xff, writer->f);
+    fputc((width >> 8) & 0xff, writer->f);
+    fputc(height & 0xff, writer->f);
+    fputc((height >> 8) & 0xff, writer->f);
+
+    fputc(0xf0, writer->f);  // there is an unsorted global color table of 2 entries
+    fputc(0, writer->f);     // background color
+    fputc(0, writer->f);     // pixels are square (we need to specify this because it's 1989)
+
+    // now the "global" palette (really just a dummy palette)
+    // color 0: black
+    fputc(0, writer->f);
+    fputc(0, writer->f);
+    fputc(0, writer->f);
+    // color 1: also black
+    fputc(0, writer->f);
+    fputc(0, writer->f);
+    fputc(0, writer->f);
+
+    if( delay != 0 )
+    {
+        // animation header
+        fputc(0x21, writer->f); // extension
+        fputc(0xff, writer->f); // application specific
+        fputc(11, writer->f); // length 11
+        fputs("NETSCAPE2.0", writer->f); // yes, really
+        fputc(3, writer->f); // 3 bytes of NETSCAPE2.0 data
+
+        fputc(1, writer->f); // JUST BECAUSE
+        fputc(0, writer->f); // loop infinitely (byte 0)
+        fputc(0, writer->f); // loop infinitely (byte 1)
+
+        fputc(0, writer->f); // block terminator
+    }
+
+    return true;
+}
+
+// Writes out a new frame to a GIF in progress.
+// The GIFWriter should have been created by GIFBegin.
+// AFAIK, it is legal to use different bit depths for different frames of an image -
+// this may be handy to save bits in animations that don't change much.
+bool GifWriteFrame( GifWriter* writer, const uint8_t* image, uint32_t width, uint32_t height, uint32_t delay, int bitDepth = 8, bool dither = false )
+{
+    if(!writer->f) return false;
+
+    const uint8_t* oldImage = writer->firstFrame? NULL : writer->oldImage;
+    writer->firstFrame = false;
+
+    GifPalette pal;
+    GifMakePalette((dither? NULL : oldImage), image, width, height, bitDepth, dither, &pal);
+
+    if(dither)
+        GifDitherImage(oldImage, image, writer->oldImage, width, height, &pal);
+    else
+        GifThresholdImage(oldImage, image, writer->oldImage, width, height, &pal);
+
+    GifWriteLzwImage(writer->f, writer->oldImage, 0, 0, width, height, delay, &pal);
+
+    return true;
+}
+
+// Writes the EOF code, closes the file handle, and frees temp memory used by a GIF.
+// Many if not most viewers will still display a GIF properly if the EOF code is missing,
+// but it's still a good idea to write it out.
+bool GifEnd( GifWriter* writer )
+{
+    if(!writer->f) return false;
+
+    fputc(0x3b, writer->f); // end of file
+    fclose(writer->f);
+    GIF_FREE(writer->oldImage);
+
+    writer->f = NULL;
+    writer->oldImage = NULL;
+
+    return true;
+}
+
+#endif