Canvas: Handle drawing images with opacity < 1

tmxlib/canvas.py

@@ -43,7 +43,7 @@ class Canvas(PilImage):
 
     def __init__(self, size=(0, 0), commands=()):
         self.size = size
-        self.pil_image = Image.new('RGBA', size)
+        self.pil_image = Image.new('RGBA', size, color=(0, 0, 0, 0))
 
         for command in commands:
             command.draw(self)
@@ -67,9 +67,11 @@ def trans(self, new_trans):
     def _parent_info(self):
         return 0, 0, self.to_image()
 
-    def draw_image(self, image, pos=(0, 0)):
+    def draw_image(self, image, pos=(0, 0), opacity=1):
         """Paste the given image at the given position
         """
+        if not opacity:
+            return
         x, y = pos
 
         try:
@@ -82,10 +84,30 @@ def draw_image(self, image, pos=(0, 0)):
             pil_image = parent.pil_image
         except AttributeError:
             input = BytesIO(parent._repr_png_())
-            pil_image = Image.open(input)
+            pil_image = Image.open(input).convert('RGBA')
         if crop:
             pil_image = pil_image.crop((image.x, image.y,
                                         image.x + image.width,
                                         image.y + image.height))
 
-        self.pil_image.paste(pil_image, (x, y))
+        if opacity == 1:
+            alpha_channel = pil_image
+            self.pil_image.paste(pil_image, (x, y), mask=alpha_channel)
+        else:
+            # Create temporary image the same size as the canvas
+            bigger_image = Image.new('RGBA',
+                                     (self.width, self.height),
+                                     color=(0, 0, 0, 0))
+            # Blit into it
+            bigger_image.paste(pil_image, (x, y))
+            # Reduce its alpha
+            bands = bigger_image.split()
+            alpha_channel = bands[3]
+            alpha_channel = alpha_channel.point(
+                lambda x: int(x * opacity))
+            bigger_image = Image.merge('RGBA', bands[:3] + (alpha_channel, ))
+            # Finally, blit it to the canvas
+            self.pil_image = Image.alpha_composite(
+                self.pil_image,
+                bigger_image)
+            # Thanks, PIL, for making this so easy!

tmxlib/draw.py

@@ -35,9 +35,11 @@ class DrawImageCommand(DrawCommand):
     """
     x, y = helpers.unpacked_properties('pos')
 
-    def __init__(self, image, pos=(0, 0)):
+    def __init__(self, image, pos=(0, 0), opacity=1):
         self.image = image
         self.pos = pos
+        self.opacity = opacity
 
     def draw(self, canvas):
-        canvas.draw_image(self.image, self.pos)
+        canvas.draw_image(self.image, self.pos,
+                          opacity=self.opacity)

tmxlib/layer.py

@@ -248,6 +248,7 @@ def generate_draw_commands(self):
                 yield draw.DrawImageCommand(
                     image=tile.image,
                     pos=(tile.pixel_x, tile.pixel_y - tile.pixel_height),
+                    opacity=self.opacity,
                 )
 
     def _repr_png_(self):

tmxlib_test/test_image.py

@@ -356,6 +356,33 @@ def test_canvas_draw_image(colorcorners_image, canvas_mod):
     assert_png_repr_equal(canvas, 'colorcorners-x4.png')
 
 
+def test_canvas_draw_image_alpha(image_class, colorcorners_image, canvas_mod):
+    canvas = canvas_mod.Canvas((32, 32))
+    scribble = load_image(image_class, 'scribble.png')
+    canvas.draw_image(scribble, opacity=0.5)
+    canvas.draw_image(colorcorners_image, pos=(8, 8), opacity=0.5)
+
+    assert_png_repr_equal(canvas, 'colorcorners-mid-alpha.png', epsilon=1)
+
+    canvas.draw_image(scribble, opacity=0)
+    assert_png_repr_equal(canvas, 'colorcorners-mid-alpha.png', epsilon=1)
+
+
+def test_canvas_command_img_alpha(image_class, colorcorners_image, canvas_mod):
+    canvas = canvas_mod.Canvas((32, 32))
+    scribble = load_image(image_class, 'scribble.png')
+    for command in (
+            tmxlib.draw.DrawImageCommand(scribble, opacity=0.5),
+            tmxlib.draw.DrawImageCommand(colorcorners_image, pos=(8, 8),
+                                         opacity=0.5)):
+        command.draw(canvas)
+
+    assert_png_repr_equal(canvas, 'colorcorners-mid-alpha.png', epsilon=1)
+
+    tmxlib.draw.DrawImageCommand(scribble, opacity=0).draw(canvas)
+    assert_png_repr_equal(canvas, 'colorcorners-mid-alpha.png', epsilon=1)
+
+
 def test_canvas_draw_overlap(image_class, canvas_mod):
     canvas = canvas_mod.Canvas((32, 32))
     canvas.draw_image(load_image(image_class, 'scribble.png'))