fix: wrong alpha while reading .dds and .tga

Signed-off-by: leo <[email protected]>

Author: love-linger

src/ViewModels/ImageSource.cs

@@ -109,9 +109,23 @@ private static ImageSource DecodeWithPfim(Stream stream, long size)
                         pixelFormat = PixelFormats.Gray8;
                         break;
                     case ImageFormat.R5g5b5:
-                    case ImageFormat.R5g5b5a1:
                         pixelFormat = PixelFormats.Bgr555;
                         break;
+                    case ImageFormat.R5g5b5a1:
+                        var pixels1 = pfiImage.DataLen / 2;
+                        data = new byte[pixels1 * 4];
+                        stride = pfiImage.Width * 4;
+                        for (var i = 0; i < pixels1; i++)
+                        {
+                            var src = BitConverter.ToUInt16(pfiImage.Data, i * 2);
+                            data[i * 4 + 0] = (byte)Math.Round((src & 0x1F) / 31F * 255); // B
+                            data[i * 4 + 1] = (byte)Math.Round(((src >> 5) & 0x1F) / 31F * 255); // G
+                            data[i * 4 + 2] = (byte)Math.Round(((src >> 10) & 0x1F) / 31F * 255); // R
+                            data[i * 4 + 3] = (byte)((src >> 15) * 255F); // A
+                        }
+
+                        alphaFormat = AlphaFormat.Unpremul;
+                        break;
                     case ImageFormat.R5g6b5:
                         pixelFormat = PixelFormats.Bgr565;
                         break;
@@ -131,10 +145,10 @@ private static ImageSource DecodeWithPfim(Stream stream, long size)
                             data[i * 4 + 3] = (byte)Math.Round(((src >> 12) & 0x0F) / 15F * 255); // A
                         }
 
-                        alphaFormat = AlphaFormat.Premul;
+                        alphaFormat = AlphaFormat.Unpremul;
                         break;
                     case ImageFormat.Rgba32:
-                        alphaFormat = AlphaFormat.Premul;
+                        alphaFormat = AlphaFormat.Unpremul;
                         break;
                     default:
                         return new ImageSource(null, 0);
@@ -165,7 +179,7 @@ private static ImageSource DecodeWithTiff(Stream stream, long size)
                 var ptr = Marshal.UnsafeAddrOfPinnedArrayElement(pixels, 0);
                 var pixelSize = new PixelSize(width, height);
                 var dpi = new Vector(96, 96);
-                var bitmap = new Bitmap(PixelFormats.Rgba8888, AlphaFormat.Premul, ptr, pixelSize, dpi, width * 4);
+                var bitmap = new Bitmap(PixelFormats.Rgba8888, AlphaFormat.Unpremul, ptr, pixelSize, dpi, width * 4);
                 return new ImageSource(bitmap, size);
             }
         }