Revert "[Web] Fix BMP encoder (#29448)"

This reverts commit 15d5a23.

Author: dkwingsmt

lib/web_ui/lib/src/ui/painting.dart

@@ -500,83 +500,71 @@ Future<void> _decodeImageFromListAsync(Uint8List list, ImageDecoderCallback call
   final FrameInfo frameInfo = await codec.getNextFrame();
   callback(frameInfo.image);
 }
-
-// Encodes the input pixels into a BMP file that supports transparency.
-//
-// The `pixels` should be the scanlined raw pixels, 4 bytes per pixel, from left
-// to right, then from top to down. The order of the 4 bytes of pixels is
-// decided by `format`.
 Future<Codec> _createBmp(
   Uint8List pixels,
   int width,
   int height,
   int rowBytes,
   PixelFormat format,
 ) {
-  late bool swapRedBlue;
-  switch (format) {
-    case PixelFormat.bgra8888:
-      swapRedBlue = true;
-      break;
-    case PixelFormat.rgba8888:
-      swapRedBlue = false;
-      break;
-  }
-
   // See https://en.wikipedia.org/wiki/BMP_file_format for format examples.
-  // The header is in the 108-byte BITMAPV4HEADER format, or as called by
-  // Chromium, WindowsV4. Do not use the 56-byte or 52-byte Adobe formats, since
-  // they're not supported.
-  const int dibSize = 0x6C /* 108: BITMAPV4HEADER */;
-  const int headerSize = dibSize + 0x0E;
-  final int bufferSize = headerSize + (width * height * 4);
+  final int bufferSize = 0x36 + (width * height * 4);
   final ByteData bmpData = ByteData(bufferSize);
   // 'BM' header
-  bmpData.setUint16(0x00, 0x424D, Endian.big);
+  bmpData.setUint8(0x00, 0x42);
+  bmpData.setUint8(0x01, 0x4D);
   // Size of data
   bmpData.setUint32(0x02, bufferSize, Endian.little);
   // Offset where pixel array begins
-  bmpData.setUint32(0x0A, headerSize, Endian.little);
+  bmpData.setUint32(0x0A, 0x36, Endian.little);
   // Bytes in DIB header
-  bmpData.setUint32(0x0E, dibSize, Endian.little);
-  // Width
+  bmpData.setUint32(0x0E, 0x28, Endian.little);
+  // width
   bmpData.setUint32(0x12, width, Endian.little);
-  // Height
+  // height
   bmpData.setUint32(0x16, height, Endian.little);
-  // Color panes (always 1)
+  // Color panes
   bmpData.setUint16(0x1A, 0x01, Endian.little);
-  // bpp: 32
-  bmpData.setUint16(0x1C, 32, Endian.little);
-  // Compression method is BITFIELDS to enable bit fields
-  bmpData.setUint32(0x1E, 3, Endian.little);
-  // Raw bitmap data size
+  // 32 bpp
+  bmpData.setUint16(0x1C, 0x20, Endian.little);
+  // no compression
+  bmpData.setUint32(0x1E, 0x00, Endian.little);
+  // raw bitmap data size
   bmpData.setUint32(0x22, width * height, Endian.little);
-  // Print DPI width
+  // print DPI width
   bmpData.setUint32(0x26, width, Endian.little);
-  // Print DPI height
+  // print DPI height
   bmpData.setUint32(0x2A, height, Endian.little);
-  // Colors in the palette
+  // colors in the palette
   bmpData.setUint32(0x2E, 0x00, Endian.little);
-  // Important colors
+  // important colors
   bmpData.setUint32(0x32, 0x00, Endian.little);
-  // Bitmask R
-  bmpData.setUint32(0x36, swapRedBlue ? 0x00FF0000 : 0x000000FF, Endian.little);
-  // Bitmask G
-  bmpData.setUint32(0x3A, 0x0000FF00, Endian.little);
-  // Bitmask B
-  bmpData.setUint32(0x3E, swapRedBlue ? 0x000000FF : 0x00FF0000, Endian.little);
-  // Bitmask A
-  bmpData.setUint32(0x42, 0xFF000000, Endian.little);
-
-  int destinationByte = headerSize;
-  final Uint32List combinedPixels = Uint32List.sublistView(pixels);
-  // BMP is scanlined from bottom to top. Rearrange here.
-  for (int rowCount = height - 1; rowCount >= 0; rowCount -= 1) {
-    int sourcePixel = rowCount * rowBytes;
-    for (int colCount = 0; colCount < width; colCount += 1) {
-      bmpData.setUint32(destinationByte, combinedPixels[sourcePixel], Endian.little);
-      destinationByte += 4;
-      sourcePixel += 1;
+
+
+  int pixelDestinationIndex = 0;
+  late bool swapRedBlue;
+  switch (format) {
+    case PixelFormat.bgra8888:
+      swapRedBlue = true;
+      break;
+    case PixelFormat.rgba8888:
+      swapRedBlue = false;
+      break;
+  }
+  for (int pixelSourceIndex = 0; pixelSourceIndex < pixels.length; pixelSourceIndex += 4) {
+    final int r = swapRedBlue ? pixels[pixelSourceIndex + 2] : pixels[pixelSourceIndex];
+    final int b = swapRedBlue ? pixels[pixelSourceIndex]     : pixels[pixelSourceIndex + 2];
+    final int g = pixels[pixelSourceIndex + 1];
+    final int a = pixels[pixelSourceIndex + 3];
+
+    // Set the pixel past the header data.
+    bmpData.setUint8(pixelDestinationIndex + 0x36, r);
+    bmpData.setUint8(pixelDestinationIndex + 0x37, g);
+    bmpData.setUint8(pixelDestinationIndex + 0x38, b);
+    bmpData.setUint8(pixelDestinationIndex + 0x39, a);
+    pixelDestinationIndex += 4;
+    if (rowBytes != width && pixelSourceIndex % width == 0) {
+      pixelSourceIndex += rowBytes - width;
     }
   }
 
@@ -815,3 +803,4 @@ class FragmentProgram {
     required Float32List floatUniforms,
   }) => throw UnsupportedError('FragmentProgram is not supported for the CanvasKit or HTML renderers.');
 }
+