Added BLP1 saving

Tests/test_file_blp.py

@@ -31,19 +31,21 @@ def test_load_blp2_dxt1a():
 
 
 def test_save(tmp_path):
-    im = hopper("P")
     f = str(tmp_path / "temp.blp")
-    im.save(f)
 
-    with Image.open(f) as reloaded:
-        assert_image_equal(im.convert("RGB"), reloaded)
-
-    with Image.open("Tests/images/transparent.png") as im:
-        f = str(tmp_path / "temp.blp")
-        im.convert("P").save(f)
+    for version in ("BLP1", "BLP2"):
+        im = hopper("P")
+        im.save(f, blp_version=version)
 
         with Image.open(f) as reloaded:
-            assert_image_similar(im, reloaded, 8)
+            assert_image_equal(im.convert("RGB"), reloaded)
+
+        with Image.open("Tests/images/transparent.png") as im:
+            f = str(tmp_path / "temp.blp")
+            im.convert("P").save(f, blp_version=version)
+
+            with Image.open(f) as reloaded:
+                assert_image_similar(im, reloaded, 8)
 
     im = hopper()
     with pytest.raises(ValueError):

src/PIL/BlpImagePlugin.py

@@ -479,13 +479,18 @@ def _save(im, fp, filename, save_all=False):
     if im.mode != "P":
         raise ValueError("Unsupported BLP image mode")
 
-    fp.write(b"BLP2")
+    magic = b"BLP1" if im.encoderinfo.get("blp_version") == "BLP1" else b"BLP2"
+    fp.write(magic)
+
     fp.write(struct.pack("<i", 1))  # Uncompressed or DirectX compression
     fp.write(struct.pack("<b", Encoding.UNCOMPRESSED))
     fp.write(struct.pack("<b", 1 if im.palette.mode == "RGBA" else 0))
     fp.write(struct.pack("<b", 0))  # alpha encoding
     fp.write(struct.pack("<b", 0))  # mips
     fp.write(struct.pack("<II", *im.size))
+    if magic == b"BLP1":
+        fp.write(struct.pack("<i", 5))
+        fp.write(struct.pack("<i", 0))
 
     ImageFile._save(im, fp, [("BLP2", (0, 0) + im.size, 0, im.mode)])