I am currently trying to make an image upload tool, which allows you to crop an image before uploading it as a profile image. The crop box is resizable, and whatever is within the bounds of the box is shown as a preview in a seperate canvas on the webpage. At the moment, I have the following code, which takes the area within the cropper on the first canvas (context) and places it on the second canvas (previewContext).
function previewCroppedImage() {
var max_height = 100;
var max_width = 100;
var height = cropper.height;
var width = cropper.width;
var scale = Math.min(max_height/height, max_width/width)
if (scale < 1) {
height *= scale;
width *= scale;
}
previewCropCanvas.width = width;
previewCropCanvas.height = height;
imgData = context.getImageData(cropper.x, cropper.y, width, height);
previewContext.putImageData(imgData, 0, 0);
}
Using other questions, i have created this code. However this code only takes the 100px X 100px area at the top left of the crop box, when that box is larger than 100 pixels. Instead, I want it to scale down the image data that it finds within the crop box, to 100 by 100px. I have shown what the tool currently looks like in the image below.
Try using the canvas ctx.scale function like this.
ScaleHeight=maxHeight/height;
ScaleWidth=maxWidth/width;
Then either before you copy the picture to the new canvas or after its in the new canvas you can run
ctx.scale(ScaleWidth,ScaleHeight);
ctx being the context of your canvas element The documentation for it can be found on the w3schools site
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