Merge pull request #1 from nulano/fix-alpha-for-overlapping-glyphs

Add tests for glyph alpha blending

Tests/fonts/LICENSE.txt

@@ -2,7 +2,6 @@
 NotoNastaliqUrdu-Regular.ttf and NotoSansSymbols-Regular.ttf, from https://github.com/googlei18n/noto-fonts
 NotoSans-Regular.ttf, from https://www.google.com/get/noto/
 NotoSansJP-Thin.otf, from https://www.google.com/get/noto/help/cjk/
-NotoColorEmoji.ttf, from https://github.com/googlefonts/noto-emoji
 AdobeVFPrototype.ttf, from https://github.com/adobe-fonts/adobe-variable-font-prototype
 TINY5x3GX.ttf, from http://velvetyne.fr/fonts/tiny
 ArefRuqaa-Regular.ttf, from https://github.com/google/fonts/tree/master/ofl/arefruqaa
@@ -25,3 +24,5 @@ FreeMono.ttf is licensed under GPLv3.
 10x20-ISO8859-1.pcf, from https://packages.ubuntu.com/xenial/xfonts-base
 
 "Public domain font.  Share and enjoy."
+
+CBDTTestFont.ttf and EBDTTestFont.ttf from https://github.com/nulano/font-tests are public domain.

Tests/test_imagefont.py

@@ -856,6 +856,19 @@ def test_bitmap_font_stroke(layout_engine):
     assert_image_similar_tofile(im, target, 0.03)
 
 
+@pytest.mark.parametrize("embedded_color", (False, True))
+def test_bitmap_blend(layout_engine, embedded_color):
+    font = ImageFont.truetype(
+        "Tests/fonts/EBDTTestFont.ttf", size=64, layout_engine=layout_engine
+    )
+
+    im = Image.new("RGBA", (128, 96), "white")
+    d = ImageDraw.Draw(im)
+    d.text((16, 16), "AA", font=font, embedded_color=embedded_color, fill="#8E2F52")
+
+    assert_image_equal_tofile(im, "Tests/images/bitmap_font_blend.png")
+
+
 def test_standard_embedded_color(layout_engine):
     txt = "Hello World!"
     ttf = ImageFont.truetype(FONT_PATH, 40, layout_engine=layout_engine)
@@ -894,15 +907,15 @@ def test_float_coord(layout_engine, fontmode):
 def test_cbdt(layout_engine):
     try:
         font = ImageFont.truetype(
-            "Tests/fonts/NotoColorEmoji.ttf", size=109, layout_engine=layout_engine
+            "Tests/fonts/CBDTTestFont.ttf", size=64, layout_engine=layout_engine
         )
 
-        im = Image.new("RGB", (150, 150), "white")
+        im = Image.new("RGB", (128, 96), "white")
         d = ImageDraw.Draw(im)
 
-        d.text((10, 10), "\U0001f469", font=font, embedded_color=True)
+        d.text((16, 16), "AB", font=font, embedded_color=True)
 
-        assert_image_similar_tofile(im, "Tests/images/cbdt_notocoloremoji.png", 6.2)
+        assert_image_equal_tofile(im, "Tests/images/cbdt.png")
     except OSError as e:  # pragma: no cover
         assert str(e) in ("unimplemented feature", "unknown file format")
         pytest.skip("freetype compiled without libpng or CBDT support")
@@ -911,17 +924,15 @@ def test_cbdt(layout_engine):
 def test_cbdt_mask(layout_engine):
     try:
         font = ImageFont.truetype(
-            "Tests/fonts/NotoColorEmoji.ttf", size=109, layout_engine=layout_engine
+            "Tests/fonts/CBDTTestFont.ttf", size=64, layout_engine=layout_engine
         )
 
-        im = Image.new("RGB", (150, 150), "white")
+        im = Image.new("RGB", (128, 96), "white")
         d = ImageDraw.Draw(im)
 
-        d.text((10, 10), "\U0001f469", "black", font=font)
+        d.text((16, 16), "AB", "green", font=font)
 
-        assert_image_similar_tofile(
+        assert_image_equal_tofile(im, "Tests/images/cbdt_mask.png")
-            im, "Tests/images/cbdt_notocoloremoji_mask.png", 6.2
-        )
     except OSError as e:  # pragma: no cover
         assert str(e) in ("unimplemented feature", "unknown file format")
         pytest.skip("freetype compiled without libpng or CBDT support")

src/PIL/ImageDraw.py

@@ -32,6 +32,7 @@
 
 import math
 import numbers
+import struct
 
 from . import Image, ImageColor
 
@@ -542,7 +543,8 @@ class ImageDraw:
                 # font.getmask2(mode="RGBA") returns color in RGB bands and mask in A
                 # extract mask and set text alpha
                 color, mask = mask, mask.getband(3)
-                color.fillband(3, (ink >> 24) & 0xFF)
+                ink_alpha = struct.pack("=i", ink)[3]
+                color.fillband(3, ink_alpha)
                 x, y = coord
                 self.im.paste(color, (x, y, x + mask.size[0], y + mask.size[1]), mask)
             else: