Added RGBA saving

Tests/test_file_dds.py

@@ -251,10 +251,18 @@ def test_save_unsupported_mode(tmp_path):
         im.save(out)
 
 
-def test_save(tmp_path):
+@pytest.mark.parametrize(
+    ("mode", "test_file"),
+    [
+        ("RGB", "Tests/images/hopper.png"),
+        ("RGBA", "Tests/images/pil123rgba.png"),
+    ],
+)
+def test_save(mode, test_file, tmp_path):
     out = str(tmp_path / "temp.dds")
-    im = hopper()
+    with Image.open(test_file) as im:
-    im.save(out)
+        assert im.mode == mode
+        im.save(out)
 
-    with Image.open(out) as reloaded:
+        with Image.open(out) as reloaded:
-        assert_image_equal(im, reloaded)
+            assert_image_equal(im, reloaded)

src/PIL/DdsImagePlugin.py

@@ -203,7 +203,7 @@ class DdsImageFile(ImageFile.ImageFile):
 
 
 def _save(im, fp, filename):
-    if im.mode != "RGB":
+    if im.mode not in ("RGB", "RGBA"):
         raise OSError(f"cannot write mode {im.mode} as DDS")
 
     fp.write(
@@ -214,24 +214,27 @@ def _save(im, fp, filename):
         )  # flags
         + o32(im.height)
         + o32(im.width)
-        + o32((im.width * 24 + 7) // 8)  # pitch
+        + o32((im.width * (32 if im.mode == "RGBA" else 24) + 7) // 8)  # pitch
         + o32(0)  # depth
         + o32(0)  # mipmaps
         + o32(0) * 11  # reserved
         + o32(32)  # pfsize
-        + o32(DDPF_RGB)  # pfflags
+        + o32(DDS_RGBA if im.mode == "RGBA" else DDPF_RGB)  # pfflags
         + o32(0)  # fourcc
-        + o32(24)  # bitcount
+        + o32(32 if im.mode == "RGBA" else 24)  # bitcount
         + o32(0xFF0000)  # rbitmask
         + o32(0xFF00)  # gbitmask
         + o32(0xFF)  # bbitmask
-        + o32(0)  # abitmask
+        + o32(0xFF000000 if im.mode == "RGBA" else 0)  # abitmask
         + o32(DDSCAPS_TEXTURE)  # dwCaps
         + o32(0)  # dwCaps2
         + o32(0)  # dwCaps3
         + o32(0)  # dwCaps4
         + o32(0)  # dwReserved2
     )
+    if im.mode == "RGBA":
+        r, g, b, a = im.split()
+        im = Image.merge("RGBA", (a, r, g, b))
     ImageFile._save(im, fp, [("raw", (0, 0) + im.size, 0, (im.mode[::-1], 0, 1))])