add shade function

Author: moononournation

src/canvas/Arduino_Canvas.cpp

@@ -613,6 +613,46 @@ void Arduino_Canvas::flushQuad(bool force_flush)
   }
 }
 
+void Arduino_Canvas::shade(int16_t x, int16_t y, int16_t w, int16_t h, uint16_t shade_mask)
+{
+  if (_rotation > 0)
+  {
+    int16_t t = x;
+    switch (_rotation)
+    {
+    case 1:
+      x = WIDTH - y - h;
+      y = t;
+      t = w;
+      w = h;
+      h = t;
+      break;
+    case 2:
+      x = WIDTH - x - w;
+      y = HEIGHT - y - h;
+      break;
+    case 3:
+      x = y;
+      y = HEIGHT - t - w;
+      t = w;
+      w = h;
+      h = t;
+      break;
+    }
+  }
+  uint16_t *row = _framebuffer;
+  row += y * WIDTH;
+  row += x;
+  for (int j = 0; j < h; j++)
+  {
+    for (int i = 0; i < w; i++)
+    {
+      row[i] &= shade_mask;
+    }
+    row += WIDTH;
+  }
+}
+
 uint16_t *Arduino_Canvas::getFramebuffer()
 {
   return _framebuffer;

src/canvas/Arduino_Canvas.h

@@ -25,8 +25,9 @@ class Arduino_Canvas : public Arduino_GFX
   void draw16bitRGBBitmapWithTranColor(int16_t x, int16_t y, uint16_t *bitmap, uint16_t transparent_color, int16_t w, int16_t h) override;
   void draw16bitBeRGBBitmap(int16_t x, int16_t y, uint16_t *bitmap, int16_t w, int16_t h) override;
   void flush(bool force_flush = false) override;
-  void flushQuad(bool force_flush = false);
 
+  void flushQuad(bool force_flush = false);
+  void shade(int16_t x, int16_t y, int16_t w, int16_t h, uint16_t shade_mask);
   uint16_t *getFramebuffer();
 
 protected: