Flutter - How to rotate an image around the center with canvas

Question

I am trying to implement a custom painter that can draw an image (scaled down version) on the canvas and the drawn image can be rotated and scaled.

I get to know that to scale the image I have to scale the canvas using scale method.

Now the questions is how to rotate the scaled image on its center (or any other point). The rotate method of canvas allow only to rotate on top left corner.

Here is my implementation that can be extended

Answer 1

Had the same problem, Solution was simply making your own rotation method in three lines

void rotate(Canvas canvas, double cx, double cy, double angle) {
  canvas.translate(cx, cy);
  canvas.rotate(angle);
  canvas.translate(-cx, -cy);
}

We thus first move the canvas towards the point you want to pivot around. We then rotate along the the topleft (default for Flutter) which in coordinate space is the pivot you want and then put the canvas back to the desired position, with the rotation applied. Method is very efficient, requiring only 4 additions for the translation and the rotation cost is identical to the original one.