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Image Manipulation In React With Konva Js

We set the ref prop for the Stage and Layer components so that we can access it directly. This is where we add the buttons to create the shapes. For the shapes provided by React Konva, we create the shapes by adding an object to the array for the shape and then map them to the shape with the properties specified by the object. We add a text area, and then we handle the events created by the text area. When the user clicks the text area, a box will with handles will be displayed to let the user move the text area around the canvas. This is what the click handler for the stage is doing.

If you have a complex or large map to render on your stage you may find that performance takes a nosedive as soon as you try to pan the stage. Panning is probably the easiest solution to implement, it requires you to add one prop to your Stage component which is draggable . In the code above, we used the useEffect Hook to load the image when our app first loads by passing an empty array to the second argument of useEffect. With React Konva, we can create a canvas with its Stage component, which has one or more Layer components nested inside. React Konva is a tool that allows us to manipulate the canvas.

Why Use Konva

Adding the transformation feature is a bit complex. We’ve to create a component that has the react konva shape, then make it draggable. Next, we have to add the onTransformationEnd prop with a function that scales the shape by the factor that the user transforms the shape to and set that as the width and height. To build the image upload feature, we add an input element which we don’t show, and we use the ref to write a function to let the user click on the hidden file input. Even better, we can add Transformers to let users change the size of the shape like they do in photo editors.

It lets us easily create shapes without calculating where each point will be, and it has lots of built-in shapes and animation features we can use to create more interactive canvases. Let’s create a separate component that contains our individual stickers which will be on the canvas. We’ll click this button whenever we want to add react konva a new sticker to the canvas. Currently you can use all Konva nodes and shapes as React components and all Konva events are supported on them in the same way. It is an attempt to make React work with the HTML5 canvas library. The goal is to have a similar declarative markup as normal React and also a similar data-flow model.

Events In Konva

In the code above, we have the handleDragStart function to set the shadow to a new color and offset as the original circle. We also expanded the shape slightly to indicate that it’s being dragged. In the code above, we referenced the Stage component, which creates the canvas. The width is set to the browser tab width, and the height is set to the browser tab height. In order to delete stickers from the canvas we add a cross icon to the top right corner of each sticker. In the KonvaImage we add the x and y properties to determine where the sticker appears on the canvas when the button is clicked.

This nested loop approach returns a nested array so you flatten it with a .reduce. We load one up, wait for the onload event to fire, add it to state, which triggers a re-render, and start the game loop timer. In this example, the red react konva line is the Stage, the blue rectangle is the image we wan’t to crop, the white dotted rectangle is the part of the image the user want’s to crop. To start, we will create a React app with the Create React App command line program.

Build Your Own Stickers Component With React

We loop through the marbles and declaratively add them to the Stage. I don’t fully understand why, but I’m sure there’s a reason. In theory, this combination has better performance than SVG+React but worse performance than raw canvas because of the additional abstraction layers.

stage and layer are the Konva Stage and Layer objects which we pass in when the addLine function is called. When the mousemove and touchend events are triggered, we set isPaint to false so we stop drawing the line. In this file, we use plain Konva since React Konva does not have a convenient way to make free drawing a line where a user drags the mouse. When the mousedown and touchstart is triggered, we set the color of the line depending on what the mode is. If it’s erase we draw a thick white line so that users can draw it over their content, letting users erase their changes. We use the Konva library to let us add the shapes/text and erase them.

Theming Vue Js With Styled

caching, event handling for desktop and mobile applications, and much more. element and use it as image attribute of ReactKonva.Image component. In the Stage component, we have a onMouseDown handler to deselect all shapes when the click is outside all the shapes. When the user clicks outside the text area, the box with handles will disappear, letting the user select other items. Using panning and zooming allows you to render content that is larger than the initial Stage while giving the user tools to interact with the content in a manner that feels familiar. The first event OnWheel will listen for a user scrolling up and down while the last two are used for touch screen devices in order to detect the user using two fingers to pinch and pull the stage.

How do I change states in react?

setState() . This is a function available to all React components that use state, and allows us to let React know that the component state has changed. This way the component knows it should re-render, because its state has changed and its UI will most likely also change.

In strict mode react-konva will update all properties of the nodes to the values that you provided in render() function, no matter changed they or not. An attempt to make React work with the HTML5 canvas library. The goal is to have similar declarative markup as normal React and to have similar data-flow model. Otherwise if x+vx is bigger than right edge, invert vx. Our game loop is a function that d3.timer calls on every requestAnimationFrame.

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