LibDraw: Support dotted lines in Painter::draw_line()

Painter::draw_line() now has an optional "bool dotted" parameter that
causes it to only render every other pixel.

Note that this only works with horizontal and vertical lines at the
moment and we'll assert if called with dotted=true for a diagonal line.

Libraries/LibDraw/Painter.cpp

@@ -71,7 +71,6 @@ void Painter::clear_rect(const Rect& a_rect, Color color)
     }
 }
 
-
 void Painter::fill_rect(const Rect& a_rect, Color color)
 {
     if (color.alpha() == 0)
@@ -774,7 +773,7 @@ void Painter::draw_pixel(const Point& position, Color color, int thickness)
     fill_rect(rect, color);
 }
 
-void Painter::draw_line(const Point& p1, const Point& p2, Color color, int thickness)
+void Painter::draw_line(const Point& p1, const Point& p2, Color color, int thickness, bool dotted)
 {
     auto clip_rect = this->clip_rect();
 
@@ -797,8 +796,13 @@ void Painter::draw_line(const Point& p1, const Point& p2, Color color, int thick
             return;
         int min_y = max(point1.y(), clip_rect.top());
         int max_y = min(point2.y(), clip_rect.bottom());
-        for (int y = min_y; y <= max_y; ++y)
-            draw_pixel({ x, y }, color, thickness);
+        if (dotted) {
+            for (int y = min_y; y <= max_y; y += 2)
+                draw_pixel({ x, y }, color, thickness);
+        } else {
+            for (int y = min_y; y <= max_y; ++y)
+                draw_pixel({ x, y }, color, thickness);
+        }
         return;
     }
 
@@ -815,11 +819,19 @@ void Painter::draw_line(const Point& p1, const Point& p2, Color color, int thick
             return;
         int min_x = max(point1.x(), clip_rect.left());
         int max_x = min(point2.x(), clip_rect.right());
-        for (int x = min_x; x <= max_x; ++x)
-            draw_pixel({ x, y }, color, thickness);
+        if (dotted) {
+            for (int x = min_x; x <= max_x; x += 2)
+                draw_pixel({ x, y }, color, thickness);
+        } else {
+            for (int x = min_x; x <= max_x; ++x)
+                draw_pixel({ x, y }, color, thickness);
+        }
         return;
     }
 
+    // FIXME: Implement dotted diagonal lines.
+    ASSERT(!dotted);
+
     const double adx = abs(point2.x() - point1.x());
     const double ady = abs(point2.y() - point1.y());
 

Libraries/LibDraw/Painter.h

@@ -26,7 +26,7 @@ public:
     void draw_bitmap(const Point&, const CharacterBitmap&, Color = Color());
     void draw_bitmap(const Point&, const GlyphBitmap&, Color = Color());
     void set_pixel(const Point&, Color);
-    void draw_line(const Point&, const Point&, Color, int thickness = 1);
+    void draw_line(const Point&, const Point&, Color, int thickness = 1, bool dotted = false);
     void draw_scaled_bitmap(const Rect& dst_rect, const GraphicsBitmap&, const Rect& src_rect);
     void blit(const Point&, const GraphicsBitmap&, const Rect& src_rect, float opacity = 1.0f);
     void blit_dimmed(const Point&, const GraphicsBitmap&, const Rect& src_rect);