Added BC5 saving

Author: radarhere

Tests/test_file_dds.py

@@ -402,7 +402,7 @@ def test_not_implemented(test_file: str) -> None:
 def test_save_unsupported_mode(tmp_path: Path) -> None:
     out = str(tmp_path / "temp.dds")
     im = hopper("HSV")
-    with pytest.raises(OSError):
+    with pytest.raises(OSError, match="cannot write mode HSV as DDS"):
         im.save(out)
 
 
@@ -424,6 +424,13 @@ def test_save(mode: str, test_file: str, tmp_path: Path) -> None:
         assert_image_equal_tofile(im, out)
 
 
+def test_save_unsupported_pixel_format(tmp_path: Path) -> None:
+    out = str(tmp_path / "temp.dds")
+    im = hopper()
+    with pytest.raises(OSError, match="cannot write pixel format UNKNOWN"):
+        im.save(out, pixel_format="UNKNOWN")
+
+
 def test_save_dxt1(tmp_path: Path) -> None:
     # RGB
     out = str(tmp_path / "temp.dds")
@@ -493,3 +500,14 @@ def test_save_dxt5(tmp_path: Path) -> None:
     im_la = im_rgba.convert("LA")
     im_la.save(out, pixel_format="DXT5")
     assert_image_similar_tofile(im_la.convert("RGBA"), out, 8.32)
+
+
+def test_save_dx10_bc5(tmp_path: Path) -> None:
+    out = str(tmp_path / "temp.dds")
+    with Image.open(TEST_FILE_DX10_BC5_TYPELESS) as im:
+        im.save(out, pixel_format="BC5")
+    assert_image_similar_tofile(im, out, 9.56)
+
+    im = hopper("L")
+    with pytest.raises(OSError, match="only RGB mode can be written as BC5"):
+        im.save(out, pixel_format="BC5")

src/PIL/DdsImagePlugin.py

@@ -530,7 +530,7 @@ def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
     bitcount = len(im.getbands()) * 8
     pixel_format = im.encoderinfo.get("pixel_format")
     args: tuple[int] | str
-    if pixel_format in ("DXT1", "BC2", "DXT3", "BC3", "DXT5"):
+    if pixel_format:
         codec_name = "bcn"
         flags |= DDSD.LINEARSIZE
         pitch = (im.width + 3) * 4
@@ -550,9 +550,18 @@ def _save(im: Image.Image, fp: IO[bytes], filename: str | bytes) -> None:
             if pixel_format == "BC2":
                 args = (2,)
                 dxgi_format = DXGI_FORMAT.BC2_TYPELESS
-            else:
+            elif pixel_format == "BC3":
                 args = (3,)
                 dxgi_format = DXGI_FORMAT.BC3_TYPELESS
+            elif pixel_format == "BC5":
+                args = (5,)
+                dxgi_format = DXGI_FORMAT.BC5_TYPELESS
+                if im.mode != "RGB":
+                    msg = "only RGB mode can be written as BC5"
+                    raise OSError(msg)
+            else:
+                msg = f"cannot write pixel format {pixel_format}"
+                raise OSError(msg)
     else:
         codec_name = "raw"
         flags |= DDSD.PITCH

src/libImaging/BcnEncode.c

@@ -185,7 +185,7 @@ encode_bc2_block(Imaging im, ImagingCodecState state, UINT8 *dst) {
 }
 
 static void
-encode_bc3_alpha(Imaging im, ImagingCodecState state, UINT8 *dst) {
+encode_bc3_alpha(Imaging im, ImagingCodecState state, UINT8 *dst, int o) {
     int i, j;
     UINT8 alpha_min = 0, alpha_max = 0;
     UINT8 block[16], current_alpha;
@@ -202,7 +202,7 @@ encode_bc3_alpha(Imaging im, ImagingCodecState state, UINT8 *dst) {
                 continue;
             }
 
-            current_alpha = (UINT8)im->image[y][x + 3];
+            current_alpha = (UINT8)im->image[y][x + o];
             block[i + j * 4] = current_alpha;
 
             if (first || current_alpha < alpha_min) {
@@ -226,12 +226,13 @@ encode_bc3_alpha(Imaging im, ImagingCodecState state, UINT8 *dst) {
             if (!current_alpha) {
                 l |= 6 << (j * 3);
                 continue;
-            } else if (current_alpha == 255 || denom == 0) {
+            } else if (current_alpha == 255) {
                 l |= 7 << (j * 3);
                 continue;
             }
 
-            float distance = abs(current_alpha - alpha_min) / denom * 10;
+            float distance =
+                denom == 0 ? 0 : abs(current_alpha - alpha_min) / denom * 10;
             if (distance < 3) {
                 l |= 2 << (j * 3);  // 4/5 * alpha_min + 1/5 * alpha_max
             } else if (distance < 5) {
@@ -257,21 +258,28 @@ ImagingBcnEncode(Imaging im, ImagingCodecState state, UINT8 *buf, int bytes) {
     UINT8 *dst = buf;
 
     for (;;) {
-        if (n == 2 || n == 3) {
-            if (has_alpha_channel) {
-                if (n == 2) {
-                    encode_bc2_block(im, state, dst);
+        if (n == 5) {
+            encode_bc3_alpha(im, state, dst, 0);
+            dst += 8;
+
+            encode_bc3_alpha(im, state, dst, 1);
+        } else {
+            if (n == 2 || n == 3) {
+                if (has_alpha_channel) {
+                    if (n == 2) {
+                        encode_bc2_block(im, state, dst);
+                    } else {
+                        encode_bc3_alpha(im, state, dst, 3);
+                    }
+                    dst += 8;
                 } else {
-                    encode_bc3_alpha(im, state, dst);
-                }
-                dst += 8;
-            } else {
-                for (int i = 0; i < 8; i++) {
-                    *dst++ = 0xff;
+                    for (int i = 0; i < 8; i++) {
+                        *dst++ = 0xff;
+                    }
                 }
             }
+            encode_bc1_color(im, state, dst, n == 1 && has_alpha_channel);
         }
-        encode_bc1_color(im, state, dst, n == 1 && has_alpha_channel);
         dst += 8;
 
         state->x += im->pixelsize * 4;