如何在 HTML Canvas 圆中居中图像？

Question

I am very new to the canvas so I have very little idea how it works. This is the code for the circle that I have drawn in the middle of the screen.

      ctx.save();
      ctx.beginPath();
      ctx.arc(canvas.width / 2, canvas.height / 2, radius, 0, 2 * Math.PI);

      ctx.strokeStyle = "#2465D3";
      ctx.stroke();
      ctx.clip();

      ctx.drawImage(imageFile, 200, 200, 500, 500);
      ctx.restore();
      ctx.stroke();

I want to show a picture inside of the circle. The picture shows up in the circle in the wrong position with this code. I want the picture to be in the center of the circle like:

According to the syntax of drawImage() , I need dx and dy in this ctx.drawImage(image, dx, dy, dWidth, dHeight) to position the image correctly on the canvas (at the center of the circle).

Is there anything I can do to put the picture in the center of the circle without doing all sorts of Pythagoras calculations?

Why I am doing it this way?

I cannot find one good coordinate for the picture and move on because the radius of the circle is not constant so that would not work. I would need to find the appropriate coordinate for the picture every time the radius of the circle changes to keep the picture in the middle of the circle.

My thought process was to find the corner coordinate of the square that the circle would make like in this picture

then to measure the distance between that point and the width of the canvas.

I think there must be a better way to do this. Is there a better way to do this? I am using this in a React App.

Answer 1

Your imagem must have the x and y position equals circle. The height and width imagem must have 2r.

x = canvas.width / 2;
y = canvas.height / 2
ctx.save();
ctx.beginPath();
ctx.arc(x,y, radius, 0, 2 * Math.PI);

ctx.strokeStyle = "#2465D3";
ctx.stroke();
ctx.clip();

ctx.drawImage(imageFile, x, y, 2 * radius, 2 * radius);
ctx.restore();
ctx.stroke();

Answer 2

Here canvas.width / 2 and canvas.height/ 2 are the coordinates for the center of the circle.

      ctx.drawImage(
        oneMoreRound,
        canvas.width / 2,
        canvas.height / 2,
        radius * 2,
        radius * 2
      );

Only passing the above code puts the top left corner of the image to the center of the circle like this:

Subtracting the radius from the x and y coordinates puts that top left corner of the image in the top left corner of the square that the circle will create. That would put the image in the right position if the image is a square.

This is the solution

      ctx.drawImage(
        oneMoreRound,
        canvas.width / 2 - radius,
        canvas.height / 2 - radius,
        radius * 2,
        radius * 2
      );