KonvaJS crop and resize - konvajs

Question

I'm using KonvaJS to create a simple Image-Editor. As a base for the image resize function I used the code from the Konva Examples (Knonva JS Image Resize). But now I'm struggling with the implementation of a crop function. On a button click, I enable the user to draw a rectangle on the stage. I then use the built-in crop function on my image with the coordinates, width and height of the drawn rectangle and crop the image. But when I resize the image before I crop it the cropped area shows the part cropped from the original sized image.
Is there an easy, build in way I'm missing to be able to crop from the resized image? Or do I have to calculate the position and size of the drawn rectangle according to the resized values of the image, then crop that part and resize and reposition the result?
Crop Image:
function cropImage(x, y, width, height, activeLayer) {
var image = activeLayer.get('Image')[0], xDiff = 0, yDiff = 0, newWidth, newHeight, newX, newY;
// only Crop visible Parts of the Image
if(x < activeLayer.getX()) {
xDiff = activeLayer.getX() - x;
}
if(y < activeLayer.getY()) {
yDiff = activeLayer.getY() - y;
}
if (x + width > activeLayer.getX() + activeLayer.width()) {
width = width - ((x + width) - (activeLayer.getX() + activeLayer.width()));
}
if (y + height > activeLayer.getY() + activeLayer.height()) {
height = height - ((y + height) - (activeLayer.getY() + activeLayer.height()));
}
newHeight = height - yDiff;
newWidth = width - xDiff;
newX = (x - activeLayer.getX()) + image.cropX() + xDiff;
newY = (y - activeLayer.getY()) + image.cropY() + yDiff;
image.width(newWidth);
image.height(newHeight);
activeLayer.width(newWidth);
activeLayer.height(newHeight);
activeLayer.setX(newX + activeLayer.getX() - image.cropX());
activeLayer.setY(newY + activeLayer.getY() - image.cropY());
image.crop({
x : newX ,
y : newY ,
width : newWidth,
height : newHeight
});
//Reposition anchors so topLeft Anchor is always in 0/0 of the grouplayer
repositionAnchors(activeLayer);
activeLayer.draw();
}

Answer 1

This is not yet a precise answer to your question but I am including here because it might show the way for you or others in the same territory of cropping.
Run the snippet full screen.
Left image is Konva, right is the original image.
Click-drag on the left image to make a selection. The left image changes to be the selection only whilst the right shows the position of the crop. Repeat the process to see how the crops build up.
I have NOT scaled the image on the canvas in this example, so it is not an exact answer to your needs at present, but useful for visualising what is happening. I can add scaling if folks think it would be useful.
// Useful frequently used variables.
var sX = 0, sY = 0, sW = 400, sH = 200; // drawing dimensions
var iW = 0, iH = 0; // image dimensions
var cropRect = {x: sX, y: sY, width: iW, height: iH}; // scaled rect
var imgRect = $('.imgRect');
var imgPtr = $('#imgPtr');
var scale = 1;
var img = $('#daImg');
var src = "https://dummyimage.com/400x200/e85de8/fff&text=SO Rocks!"
$('.container').css({width: sW, height: sH});
// Vars for mouse rect work.
var posStart, posNow, mode = '';
// Set up add a stage & layer
var s1 = new Konva.Stage({container: 'container', width: sW, height: sH});
var l1 = new Konva.Layer({});
s1.add(l1);
var image = new Konva.Image({}) // prepare an image to display the picture.
l1.add(image);
// I use a foreground rect to catch events - this covers the konva image completely - you can wire your events in your own way
var r1 = new Konva.Rect({x: 0, y: 0, width: sW, height: sH, fill: 'gold', opacity: 0 })
l1.add(r1)
// draw a rectangle to be used as the rubber-band area
var r2 = new Konva.Rect({x: 0, y: 0, width: 0, height: 0, stroke: 'red', dash: [2,2]})
r2.listening(false); // stop r2 catching our mouse events otherwise if we reverse mouse direction events may not fire
l1.add(r2)
// Mouse movement funcs
function startDrag(posIn){
posStart = {x: posIn.x, y: posIn.y};
posNow = {x: posIn.x, y: posIn.y};
}
// update rubber rect position
function updateDrag(posIn){
posNow = {x: posIn.x, y: posIn.y};
var posRect = reverse(posStart,posNow);
r2.x(posRect.x1);
r2.y(posRect.y1);
r2.width(posRect.x2 - posRect.x1);
r2.height(posRect.y2 - posRect.y1);
r2.visible(true);
s1.draw(); // redraw any changes.
sayRect(r2);
showImgRect(r2);
}
// start the rubber rect drawing on mouse down.
r1.on('mousedown', function(e){
mode = 'drawing';
startDrag({x: e.evt.layerX, y: e.evt.layerY})
})
// update the rubber rect on mouse move - note use of 'mode' var to avoid drawing after mouse released.
r1.on('mousemove', function(e){
if (mode === 'drawing'){
updateDrag({x: e.evt.layerX, y: e.evt.layerY})
}
showImgPtr(e.evt.layerX, e.evt.layerY);
sayPos(e.evt.layerX, e.evt.layerY);
})
// When user releases the mouse we note the size and modify the clip rect.
r1.on('mouseup', function(e){
mode = '';
r2.visible(false);
// leave a rect to show the target
imgRect.hide();
var imgRect2 = imgRect.clone();
imgRect2
.appendTo('#container2')
.addClass('deleteMe')
.show();
setCrop(r2);
sayInfo(img, image);
})
// Draw a rect on the original image to show location and size. Just using some simple jquery to manipulate a div.
function showImgRect(r){
imgRect.css({
left: r.x() + cropRect.x,
top: r.y() + cropRect.y,
width: r.width() * 1,
height: r.height() * 1
})
imgRect.show();
}
// show a mouse pointer on the original image so we get a sense of what is going on
function showImgPtr(x, y){
imgPtr.css({ left: cropRect.x + x, top: cropRect.y + y})
}
// Set the new crop rect, taking account of previous crops
function setCrop(r){
image.cropX(r.x() + cropRect.x);
image.cropY(r.y() + cropRect.y);
image.cropWidth(r.width() * scale);
image.cropHeight(r.height() * scale);
image.width(r.width());
image.height(r.height());
l1.draw();
cropRect = {x: cropRect.x + r.x(), y: cropRect.y + r.y(), width: r.width(), height: r.height()};
}
// This event listener is fired when the image is loaded - could be a few secs delay for a big image
// so this is effectively an async technique.
img.on('load', function() {
// note the dimensions
iW = img.width();
iH = img.height();
// set the konva image details
image.x(sX);
image.y(sY);
image.width(iW);
image.height(iH);
image.image(img[0]);
sayInfo(img, image);
l1.draw(); // redraw the layer to see what happened
});
// This innocent looking line intiates the image load and ultimately fires the event above.
img.prop('src', src);
/*
From here down is utility stuff
*/
// Say something useful
function sayInfo(img, image){
$('#imgInfo').html("HTML Image size " + img.width() + " x " + img.height());
$('#imageInfo').html("Konva.image " + image.x() + ", " + image.y() + " - " + image.width() + " x " + image.height());
var info = $('#info');
}
function sayRect(r){
var rectInfo = $('#rectInfo');
rectInfo.html("Clip rect on canvas " + r.x() + ", " + r.y() + " - " + r.width() + " x " + r.height());
}
function sayPos(x, y){
var posInfo = $('#posInfo');
posInfo.html("Pos on stage " + x + ", " + y);
}
// This is just to reverse co-ords if user drags left / up
function reverse(r1, r2){
var r1x = r1.x, r1y = r1.y, r2x = r2.x, r2y = r2.y, d;
if (r1x > r2x ){
d = Math.abs(r1x - r2x);
r1x = r2x; r2x = r1x + d;
}
if (r1y > r2y ){
d = Math.abs(r1y - r2y);
r1y = r2y; r2y = r1y + d;
}
return ({x1: r1x, y1: r1y, x2: r2x, y2: r2y}); // return the corrected rect.
}
// reset function
function reset(){
sX = 0; sY = 0; sW = 400; sH = 300; // drawing dimensions
iW = 0; iH = 0; // image dimensions
iW = img.width();
iH = img.height();
cropRect = {x: sX, y: sY, width: iW, height: iH}; // scaled rect
scale = 1;
if (image){
console.log('iH=' +iH);
image.x(sX);
image.y(sY);
image.width(iW);
image.height(iH);
image.cropX(sX);
image.cropY(sY);
image.cropWidth(iW);
image.cropHeight(iH);
}
$('.deleteMe').remove();
$('.imgRect').hide();
l1.draw();
}
$('#reset').on('click', function(){reset()});
p
{
padding: 5px;
}
.container {
position: relative;
display: inline-block;
width: 500px;
height: 400px;
background-color: transparent;
overflow: hidden;
border: 1px solid silver;
}
.imgRect {
position: absolute;
border: 1px dotted red;
background-color: Aqua;
opacity: 0.3;
}
#imgPtr {
position: absolute;
background-color: red;
width: 1px;
height: 1px;
border-radius: 50%;
border: 2px solid red;
}
a {
color: red;
cursor: pointer;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
<script src="https://cdn.rawgit.com/konvajs/konva/1.6.5/konva.min.js"></script>
<p>
<span id='text'>How crop rect relates to original image. First image is the Konva stage, second is the original image. Use click and drag to draw successive rects on the Konva image.</span> <a id='reset'>Reset</a>
</p>
<p>
<span id='imgInfo'></span><br />
<span id='imageInfo'></span>
<span id='rectInfo'>Rect info </span><br/>
<span id='posInfo'>Pos on stage </span><br/>
<span id='scaleInfo'>Scale 1:1 </span>
</p>
<div id='container' class='container'></div>
<div id='container2' class='container'>
<img id='daImg' />
<div class='imgRect'></div>
<div id='imgPtr'></div>
</div>

Answer 2

When resizing i preserve the ratio for width and height in an array and calculate the position and dimension of the rectangle which is drawn for the crop :
cropX = ((x / ratios[id].width) - (activeLayer.getX() / ratios[id].width)) + (image.cropX()) + (xDiff / ratios[id].width);
cropY = ((y / ratios[id].height)- (activeLayer.getY() / ratios[id].height)) + (image.cropY()) + (yDiff / ratios[id].height);
cropWidth = (width / ratios[id].width) - (xDiff / ratios[id].width),
cropHeight = (height / ratios[id].height) - (yDiff / ratios[id].height)