Added RGB saving

Tests/test_file_dds.py

@@ -5,7 +5,7 @@ import pytest
 
 from PIL import DdsImagePlugin, Image
 
-from .helper import assert_image_equal, assert_image_equal_tofile
+from .helper import assert_image_equal, assert_image_equal_tofile, hopper
 
 TEST_FILE_DXT1 = "Tests/images/dxt1-rgb-4bbp-noalpha_MipMaps-1.dds"
 TEST_FILE_DXT3 = "Tests/images/dxt3-argb-8bbp-explicitalpha_MipMaps-1.dds"
@@ -242,3 +242,19 @@ def test_unimplemented_pixel_format():
     with pytest.raises(NotImplementedError):
         with Image.open("Tests/images/unimplemented_pixel_format.dds"):
             pass
+
+
+def test_save_unsupported_mode(tmp_path):
+    out = str(tmp_path / "temp.dds")
+    im = hopper("HSV")
+    with pytest.raises(OSError):
+        im.save(out)
+
+
+def test_save(tmp_path):
+    out = str(tmp_path / "temp.dds")
+    im = hopper()
+    im.save(out)
+
+    with Image.open(out) as reloaded:
+        assert_image_equal(im, reloaded)

src/PIL/DdsImagePlugin.py

@@ -14,6 +14,7 @@ import struct
 from io import BytesIO
 
 from . import Image, ImageFile
+from ._binary import o32le as o32
 
 # Magic ("DDS ")
 DDS_MAGIC = 0x20534444
@@ -201,9 +202,43 @@ class DdsImageFile(ImageFile.ImageFile):
         pass
 
 
+def _save(im, fp, filename):
+    if im.mode != "RGB":
+        raise OSError(f"cannot write mode {im.mode} as DDS")
+
+    fp.write(
+        o32(DDS_MAGIC)
+        + o32(124)  # header size
+        + o32(
+            DDSD_CAPS | DDSD_HEIGHT | DDSD_WIDTH | DDSD_PITCH | DDSD_PIXELFORMAT
+        )  # flags
+        + o32(im.height)
+        + o32(im.width)
+        + o32((im.width * 24 + 7) // 8)  # pitch
+        + o32(0)  # depth
+        + o32(0)  # mipmaps
+        + o32(0) * 11  # reserved
+        + o32(32)  # pfsize
+        + o32(DDPF_RGB)  # pfflags
+        + o32(0)  # fourcc
+        + o32(24)  # bitcount
+        + o32(0xFF0000)  # rbitmask
+        + o32(0xFF00)  # gbitmask
+        + o32(0xFF)  # bbitmask
+        + o32(0)  # abitmask
+        + o32(DDSCAPS_TEXTURE)  # dwCaps
+        + o32(0)  # dwCaps2
+        + o32(0)  # dwCaps3
+        + o32(0)  # dwCaps4
+        + o32(0)  # dwReserved2
+    )
+    ImageFile._save(im, fp, [("raw", (0, 0) + im.size, 0, (im.mode[::-1], 0, 1))])
+
+
 def _accept(prefix):
     return prefix[:4] == b"DDS "
 
 
 Image.register_open(DdsImageFile.format, DdsImageFile, _accept)
+Image.register_save(DdsImageFile.format, _save)
 Image.register_extension(DdsImageFile.format, ".dds")