Optimize CompressedImage to get only bitmap information

When we create a CompressedImage from a Brush image, we want to know what
pixels are != the mask color, just to generate the PointShape (we don't
care the specific color of the scaneline/each pixel, that information is
used in the "ink processing" step).

src/app/tools/point_shapes.h

@@ -39,7 +39,7 @@ public:
 
   void preparePointShape(ToolLoop* loop) override {
     m_brush = loop->getBrush();
-    m_compressedImage.reset(new CompressedImage(m_brush->image()));
+    m_compressedImage.reset(new CompressedImage(m_brush->image(), false));
     m_firstPoint = true;
   }
 

src/doc/compressed_image.cpp

@@ -14,27 +14,33 @@
 
 namespace doc {
 
-CompressedImage::CompressedImage(const Image* image)
+CompressedImage::CompressedImage(const Image* image, bool diffColors)
   : m_image(image)
 {
-  color_t mask = image->maskColor();
+  color_t c1, c2, mask = image->maskColor();
 
   for (int y=0; y<image->height(); ++y) {
     Scanline scanline(y);
 
-    for (int x=0; x<image->width(); ++x) {
-      scanline.color = get_pixel(image, x, y);
-
-      if (scanline.color != mask) {
+    for (int x=0; x<image->width(); ) {
+      c1 = get_pixel(image, x, y);
+      if (c1 != mask) {
+        scanline.color = c1;
         scanline.x = x;
 
-        for (; x<image->width(); ++x)
-          if (!get_pixel(image, x, y))
+        for (++x; x<image->width(); ++x) {
+          c2 = get_pixel(image, x, y);
+
+          if ((diffColors && c1 != c2) ||
+              (!diffColors && c2 == mask))
             break;
+        }
 
         scanline.w = x - scanline.x;
         m_scanlines.push_back(scanline);
       }
+      else
+        ++x;
     }
   }
 }

src/doc/compressed_image.h

@@ -26,7 +26,11 @@ namespace doc {
     typedef std::vector<Scanline> Scanlines;
     typedef Scanlines::const_iterator const_iterator;
 
-    CompressedImage(const Image* image);
+    // If diffColors is true, it generates one Scanline instance for
+    // each different color. If it's false, it generates a scanline
+    // for each row of consecutive pixels different than the mask
+    // color.
+    CompressedImage(const Image* image, bool diffColors);
 
     const_iterator begin() const { return m_scanlines.begin(); }
     const_iterator end() const { return m_scanlines.end(); }