Once the image is loaded, cropped, and displayed on the canvas, what is the best way to implement image rotation functionality for the user before converting it to base64?

Question

Once the image is loaded, cropped, and displayed on the canvas, what is the best way to implement image rotation functionality for the user before converting it to base64?

My process involves cropping images to a square shape and drawing them onto a canvas.

    if(img.height >= img.width) {
        ctx.drawImage(img, 0, 0, 110, 110 * img.height / img.width);
    } else {
        ctx.drawImage(img, 0 , 0, 110 * img.width / img.height, 110);
    }

Once the image is drawn, I then convert it to base64 using canvas.toDataURL(); before sending it to the server via a POST request.

However, I also want to give users the option to rotate the image by 90 degrees prior to conversion and submission.

To see a test setup of my process, click HERE

javascript jquery html css canvas

Answer 1

Answer №1

Follow these steps to rotate a cropped image on a temporary canvas:

After that, you can use tempCanvas.toDataURL for your POST request.

Start by creating a temporary offscreen canvas
Adjust the size of the temp canvas to fit the resized and rotated image
Move to the center of the temp canvas
Rotate the image by 90 degrees
Draw the resized image on the temp canvas

Demonstration: http://jsfiddle.net/m1erickson/VrV38/

Example code:

// Create a temporary canvas

var tempCanvas=document.createElement('canvas');
var tempCtx=tempCanvas.getContext('2d');

// Resize the tempCanvas

tempCanvas.width=h;
tempCanvas.height=w;

// Translate, rotate, and draw the resized image on tempCanvas

tempCtx.translate(h/2,w/2);
tempCtx.rotate(Math.PI/2);
tempCtx.drawImage(canvas, 0,0,w,h, -w/2,-h/2,w,h);

Answer 2

Follow these steps to rotate a cropped image on a temporary canvas:

After that, you can use tempCanvas.toDataURL for your POST request.

Start by creating a temporary offscreen canvas
Adjust the size of the temp canvas to fit the resized and rotated image
Move to the center of the temp canvas
Rotate the image by 90 degrees
Draw the resized image on the temp canvas

Demonstration: http://jsfiddle.net/m1erickson/VrV38/

Example code:

// Create a temporary canvas

var tempCanvas=document.createElement('canvas');
var tempCtx=tempCanvas.getContext('2d');

// Resize the tempCanvas

tempCanvas.width=h;
tempCanvas.height=w;

// Translate, rotate, and draw the resized image on tempCanvas

tempCtx.translate(h/2,w/2);
tempCtx.rotate(Math.PI/2);
tempCtx.drawImage(canvas, 0,0,w,h, -w/2,-h/2,w,h);

Once the image is loaded, cropped, and displayed on the canvas, what is the best way to implement image rotation functionality for the user before converting it to base64?

Answer №1

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