why use c will be a lot faster, Is the dart vm the problem? Or something else?

[GanZhiXiong]

I looked at the code for your converter. C file，It is almost the same as the code I found from this issue（https://github.com/flutter/flutter/issues/26348#issuecomment-462321428）, why is the code of c fast Your code：

uint32_t *convertImage(uint8_t *plane0, uint8_t *plane1, uint8_t *plane2, int bytesPerRow, int bytesPerPixel, int width, int height){
     int hexFF = 255;
    int x, y, uvIndex, index;
    int yp, up, vp;
    int r, g, b;
    int rt, gt, bt;

    uint32_t *image = malloc(sizeof(uint32_t) * (width * height));

    for(x = 0; x < width; x++){
        for(y = 0; y < height; y++){
            
            uvIndex = bytesPerPixel * ((int) floor(x/2)) + bytesPerRow * ((int) floor(y/2));
            index = y*width+x;

            yp = plane0[index];
            up = plane1[uvIndex];
            vp = plane2[uvIndex];
            rt = round(yp + vp * 1436 / 1024 - 179);
            gt = round(yp - up * 46549 / 131072 + 44 - vp * 93604 / 131072 + 91);
            bt = round(yp + up * 1814 / 1024 - 227);
            r = clamp(0, 255, rt);
            g = clamp(0, 255, gt);
            b = clamp(0, 255, bt);
            image[getRotatedImageByteIndex(y, x, height)] = (hexFF << 24) | (b << 16) | (g << 8) | r;
        }
    }
    return image;
}

my code

Future<Image> convertYUV420toImageColor(CameraImage image) async {
      try {
        final int width = image.width;
        final int height = image.height;
        final int uvRowStride = image.planes[1].bytesPerRow;
        final int uvPixelStride = image.planes[1].bytesPerPixel;

        print("uvRowStride: " + uvRowStride.toString());
        print("uvPixelStride: " + uvPixelStride.toString());
        
        // imgLib -> Image package from https://pub.dartlang.org/packages/image
        var img = imglib.Image(width, height); // Create Image buffer

        // Fill image buffer with plane[0] from YUV420_888
        for(int x=0; x < width; x++) {
          for(int y=0; y < height; y++) {
            final int uvIndex = uvPixelStride * (x/2).floor() + uvRowStride*(y/2).floor();
            final int index = y * width + x;

            final yp = image.planes[0].bytes[index];
            final up = image.planes[1].bytes[uvIndex];
            final vp = image.planes[2].bytes[uvIndex];
            // Calculate pixel color
            int r = (yp + vp * 1436 / 1024 - 179).round().clamp(0, 255);
            int g = (yp - up * 46549 / 131072 + 44 -vp * 93604 / 131072 + 91).round().clamp(0, 255);
            int b = (yp + up * 1814 / 1024 - 227).round().clamp(0, 255);     
            // color: 0x FF  FF  FF  FF 
            //           A   B   G   R
            img.data[index] = (0xFF << 24) | (b << 16) | (g << 8) | r;
          }
        }

        imglib.PngEncoder pngEncoder = new imglib.PngEncoder(level: 0, filter: 0);
        List<int> png = pngEncoder.encodeImage(img);
        muteYUVProcessing = false;
        return Image.memory(png);  
      } catch (e) {
        print(">>>>>>>>>>>> ERROR:" + e.toString());
      }
      return null;
  }

[GanZhiXiong]

Looking forward to your reply, thanks for your code, thanks for your reply!😀

[ugu11]

You're welcome :)

I'm gonna be honest and I don't really know how the code is compiled in Flutter, but usually C code is faster because it is compiled to machine code which isn't the case with other languages and I believe that it is the case with Flutter. Also, notice that on my function I don't encode the image to png like on yours, so that also helps it being faster.

But once again, I'm not sure about that compiling aspect, so if anyone sees that it wrong feel free to share :)