Change the opacity outside of a cropping rectangle in konva - reactjs

Question

I'm trying to build a image cropping tool with React and konva. I'd like to change the opacity outside of the cropping rectangle to blur the rest of the image.
I have so far tried to set different opacities to the rectangle and the image but failed. I have looked up and there is no direct way to doing this
Here's the cropping function that I adapted to react with the help of this answer
import React, { useState, useEffect, useRef } from "react";
import { render } from "react-dom";
import { Stage, Layer, Rect, Image } from "react-konva";
import Konva from "konva";
const App = () => {
// Stage dims
let sW = 720,
sH = 720,
sX = 0,
sY = 0;
let src = "https://dummyimage.com/720x720/e85de8/fff&text=SO Rocks!";
let img = document.createElement("img");
useEffect(() => {
img.src = src;
function loadStatus() {
setloading(false);
}
img.addEventListener("load", loadStatus);
return () => {
img.removeEventListener("load", loadStatus);
};
}, [img, src]);
let scale = 1;
const [loading, setloading] = useState(true);
const [posStart, setposStart] = useState({});
const [posNow, setposNow] = useState({});
const [mode, setmode] = useState("");
/**
* Sets the state of posStart and posNow for tracking the coordinates of the cropping rectangle
* #param {Object} posIn - Coordinates of the pointer when MouseDown is fired
*/
function startDrag(posIn) {
setposStart({ x: posIn.x, y: posIn.y });
setposNow({ x: posIn.x, y: posIn.y });
}
/**
* Updates the state accordingly when the MouseMove event is fired
* #param {Object} posIn - Coordiantes of the current position of the pointer
*/
function updateDrag(posIn) {
setposNow({ x: posIn.x, y: posIn.y });
let posRect = reverse(posStart, posNow);
r2.current.x(posRect.x1);
r2.current.y(posRect.y1);
r2.current.width(posRect.x2 - posRect.x1);
r2.current.height(posRect.y2 - posRect.y1);
r2.current.visible(true);
}
/**
* Reverse coordinates if dragged left or up
* #param {Object} r1 - Coordinates of the starting position of cropping rectangle
* #param {Object} r2 - Coordinates of the current position of cropping rectangle
*/
function reverse(r1, r2) {
let 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.
}
/**
* Crops the image and saves it in jpeg format
* #param {Konva.Rect} r - Ref of the cropping rectangle
*/
function setCrop(r) {
let jpeg = new Konva.Image({
image: img,
x: sX,
y: sY
});
jpeg.cropX(r.x());
jpeg.cropY(r.y());
jpeg.cropWidth(r.width() * scale);
jpeg.cropHeight(r.height() * scale);
jpeg.width(r.width());
jpeg.height(r.height());
const url = jpeg.toDataURL({ mimeType: "image/jpeg", quality: "1.0" });
const a = document.createElement("a");
a.href = url;
a.download = "cropped.jpg";
a.click();
}
// Foreground rect to capture events
const r1 = useRef();
// Cropping rect
const r2 = useRef();
const image = useRef();
return (
<div className="container">
<Stage width={sW} height={sH}>
<Layer>
{!loading && (
<Image
ref={image}
{...{
image: img,
x: sX,
y: sY
}}
/>
)}
<Rect
ref={r1}
{...{
x: 0,
y: 0,
width: sW,
height: sH,
fill: "white",
opacity: 0
}}
onMouseDown={function (e) {
setmode("drawing");
startDrag({ x: e.evt.layerX, y: e.evt.layerY });
}}
onMouseMove={function (e) {
if (mode === "drawing") {
updateDrag({ x: e.evt.layerX, y: e.evt.layerY });
image.current.opacity(0.5);
r2.current.opacity(1);
}
}}
onMouseUp={function (e) {
setmode("");
r2.current.visible(false);
setCrop(r2.current);
image.current.opacity(1);
}}
/>
<Rect
ref={r2}
listening={false}
{...{
x: 0,
y: 0,
width: 0,
height: 0,
stroke: "white",
dash: [5, 5]
}}
/>
</Layer>
</Stage>
</div>
);
};
render(<App />, document.getElementById("root"));
Demo for the above code

Answer 1

It can be done using Konva.Group and its clip property. Add a new Konva.Image to the group and set its clipping positions and size to be the same as the cropping rectangle. Don't forget to set the listening prop of the group to false otherwise it will complicate things. Here's the final result
import { render } from "react-dom";
import React, { useLayoutEffect, useRef, useState } from "react";
import { Stage, Layer, Image, Rect, Group } from "react-konva";
/**
* Crops a portion of image in Konva stage and saves it in jpeg format
* #param {*} props - Takes no props
*/
function Cropper(props) {
// Stage dims
let sW = 720,
sH = 720,
sX = 0,
sY = 0;
let src = "https://dummyimage.com/720x720/e85de8/fff&text=SO Rocks!";
let img = new window.Image();
useLayoutEffect(() => {
img.src = src;
function loadStatus() {
// img.crossOrigin = "Anonymous";
setloading(false);
}
img.addEventListener("load", loadStatus);
return () => {
img.removeEventListener("load", loadStatus);
};
}, [img, src]);
let i = new Konva.Image({
x: 0,
y: 0,
width: 0,
height: 0
});
let scale = 1;
const [loading, setloading] = useState(true);
const [posStart, setposStart] = useState({});
const [posNow, setposNow] = useState({});
const [mode, setmode] = useState("");
/**
* Sets the state of posStart and posNow for tracking the coordinates of the cropping rectangle
* #param {Object} posIn - Coordinates of the pointer when MouseDown is fired
*/
function startDrag(posIn) {
setposStart({ x: posIn.x, y: posIn.y });
setposNow({ x: posIn.x, y: posIn.y });
}
/**
* Updates the state accordingly when the MouseMove event is fired
* #param {Object} posIn - Coordiantes of the current position of the pointer
*/
function updateDrag(posIn) {
setposNow({ x: posIn.x, y: posIn.y });
let posRect = reverse(posStart, posNow);
r2.current.x(posRect.x1);
r2.current.y(posRect.y1);
r2.current.width(posRect.x2 - posRect.x1);
r2.current.height(posRect.y2 - posRect.y1);
r2.current.visible(true);
grp.current.clip({
x: posRect.x1,
y: posRect.y1,
width: posRect.x2 - posRect.x1,
height: posRect.y2 - posRect.y1
});
grp.current.add(i);
i.image(img);
i.width(img.width);
i.height(img.height);
i.opacity(1);
}
/**
* Reverse coordinates if dragged left or up
* #param {Object} r1 - Coordinates of the starting position of cropping rectangle
* #param {Object} r2 - Coordinates of the current position of cropping rectangle
*/
function reverse(r1, r2) {
let 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.
}
/**
* Crops the image and saves it in jpeg format
* #param {Konva.Rect} r - Ref of the cropping rectangle
*/
function setCrop(r) {
let jpeg = new Konva.Image({
image: img,
x: sX,
y: sY
});
jpeg.cropX(r.x());
jpeg.cropY(r.y());
jpeg.cropWidth(r.width() * scale);
jpeg.cropHeight(r.height() * scale);
jpeg.width(r.width());
jpeg.height(r.height());
const url = jpeg.toDataURL({ mimeType: "image/jpeg", quality: "1.0" });
const a = document.createElement("a");
a.href = url;
a.download = "cropped.jpg";
a.click();
}
// Foreground rect to capture events
const r1 = useRef();
// Cropping rect
const r2 = useRef();
const image = useRef();
const grp = useRef();
return (
<div className="container">
<Stage width={sW} height={sH}>
<Layer>
{!loading && (
<Image
ref={image}
listening={false}
{...{
image: img,
x: sX,
y: sY
}}
/>
)}
<Rect
ref={r1}
{...{
x: 0,
y: 0,
width: sW,
height: sH,
fill: "white",
opacity: 0
}}
onMouseDown={function (e) {
setmode("drawing");
startDrag({ x: e.evt.layerX, y: e.evt.layerY });
image.current.opacity(0.2);
}}
onMouseMove={function (e) {
if (mode === "drawing") {
updateDrag({ x: e.evt.layerX, y: e.evt.layerY });
}
}}
onMouseUp={function (e) {
setmode("");
r2.current.visible(false);
setCrop(r2.current);
image.current.opacity(1);
grp.current.removeChildren(i);
}}
/>
<Group listening={false} ref={grp}></Group>
<Rect
ref={r2}
listening={false}
{...{
x: 0,
y: 0,
width: 0,
height: 0,
stroke: "white",
dash: [5, 10]
}}
/>
</Layer>
</Stage>
</div>
);
}
render(<Cropper />, document.getElementById("root"));
Thanks to #Vanquished Wombat for all the precious inputs. This is an adaptation of his answer here
Demo of the above code