Fix preview of certain tools in tiled mode (fix #2145)

Fixes #2145 and https://community.aseprite.org/t/3833
Regression introduced in: 6a88713213

src/app/ui/editor/editor.cpp

@@ -2692,6 +2692,26 @@ void Editor::expandRegionByTiledMode(gfx::Region& rgn,
   }
 }
 
+void Editor::collapseRegionByTiledMode(gfx::Region& rgn) const
+{
+  auto canvasSize = this->canvasSize();
+  rgn &= gfx::Region(gfx::Rect(canvasSize));
+
+  const int sprW = m_sprite->width();
+  const int sprH = m_sprite->height();
+
+  gfx::Region newRgn;
+  for (int v=0; v<canvasSize.h; v+=sprH) {
+    for (int u=0; u<canvasSize.w; u+=sprW) {
+      gfx::Region tmp(gfx::Rect(u, v, sprW, sprH));
+      tmp &= rgn;
+      tmp.offset(-u, -v);
+      newRgn |= tmp;
+    }
+  }
+  rgn = newRgn;
+}
+
 bool Editor::isMovingPixels() const
 {
   return (dynamic_cast<MovingPixelsState*>(m_state.get()) != nullptr);

src/app/ui/editor/editor.h

@@ -192,6 +192,7 @@ namespace app {
     gfx::Point mainTilePosition() const;
     void expandRegionByTiledMode(gfx::Region& rgn,
                                  const bool withProj) const;
+    void collapseRegionByTiledMode(gfx::Region& rgn) const;
 
     // Changes the scroll to see the given point as the center of the editor.
     void centerInSpritePoint(const gfx::Point& spritePos);

src/app/ui/editor/tool_loop_impl.cpp

@@ -279,8 +279,11 @@ public:
     for (auto e : UIContext::instance()->getAllEditorsIncludingPreview(m_document)) {
       gfx::Region viewportRegion;
       e->getDrawableRegion(viewportRegion, Widget::kCutTopWindows);
-      for (auto rc : viewportRegion)
-        allVisibleRgn |= gfx::Region(e->screenToEditor(rc).inflate(1, 1));
+      for (auto rc : viewportRegion) {
+        gfx::Region subrgn(e->screenToEditor(rc).inflate(1, 1));
+        e->collapseRegionByTiledMode(subrgn);
+        allVisibleRgn |= subrgn;
+      }
     }
 
     rgn &= allVisibleRgn;