add bitmap conversion to utils

thermion_dart/lib/src/utils/src/image.dart

@@ -0,0 +1,46 @@
+import 'dart:typed_data';
+
+Future<Uint8List> pixelBufferToBmp(
+    Uint8List pixelBuffer, int width, int height) async {
+  final rowSize = (width * 3 + 3) & ~3;
+  final padding = rowSize - (width * 3);
+  final fileSize = 54 + rowSize * height;
+
+  final data = Uint8List(fileSize);
+  final buffer = data.buffer;
+  final bd = ByteData.view(buffer);
+
+  // BMP file header (14 bytes)
+  bd.setUint16(0, 0x4D42, Endian.little); // 'BM'
+  bd.setUint32(2, fileSize, Endian.little);
+  bd.setUint32(10, 54, Endian.little); // Offset to pixel data
+
+  // BMP info header (40 bytes)
+  bd.setUint32(14, 40, Endian.little); // Info header size
+  bd.setInt32(18, width, Endian.little);
+  bd.setInt32(22, -height, Endian.little); // Negative for top-down
+  bd.setUint16(26, 1, Endian.little); // Number of color planes
+  bd.setUint16(28, 24, Endian.little); // Bits per pixel (RGB)
+  bd.setUint32(30, 0, Endian.little); // No compression
+  bd.setUint32(34, rowSize * height, Endian.little); // Image size
+  bd.setInt32(38, 2835, Endian.little); // X pixels per meter
+  bd.setInt32(42, 2835, Endian.little); // Y pixels per meter
+
+  // Pixel data (BMP stores in BGR format)
+  for (var y = 0; y < height; y++) {
+    for (var x = 0; x < width; x++) {
+      final srcIndex = (y * width + x) * 4; // RGBA format
+      final dstIndex = 54 + y * rowSize + x * 3; // BGR format
+      data[dstIndex] = pixelBuffer[srcIndex + 2]; // Blue
+      data[dstIndex + 1] = pixelBuffer[srcIndex + 1]; // Green
+      data[dstIndex + 2] = pixelBuffer[srcIndex]; // Red
+      // Alpha channel is discarded
+    }
+    // Add padding to the end of each row
+    for (var p = 0; p < padding; p++) {
+      data[54 + y * rowSize + width * 3 + p] = 0;
+    }
+  }
+
+  return data;
+}

thermion_dart/lib/src/utils/utils.dart

@@ -2,3 +2,4 @@ library;
 
 export 'src/geometry.dart';
 export 'src/axis.dart';
+export 'src/image.dart';