javascript - Fabric.js background appears only after click - Stack Overflow

admin管理员组

文章数量:1389768

With the following code I create a Fabric canvas

canvas = new fabric.Canvas('canvas');
canvas.setWidth(660);
canvas.setHeight(590);

fabric.Image.fromURL('assets/img/materials/marble.bmp', function(image) {
    image.set({
        // I need this because the image size and the canvas size could be different
        // in this way the image always covers the canvas
        width:660,
        height:590
    });

    canvas.setBackgroundImage(image);
});

canvas.renderAll();

The canvas is created, but the background image doesn't appear unless I click inside the canvas, as I click inside the canvas the background appears.

I'm working on my local machine and the application will not be published online.

Why do you think that I'm having this problem? Am I doing anything wrong? How could I fix this behaviour?

With the following code I create a Fabric canvas

canvas = new fabric.Canvas('canvas');
canvas.setWidth(660);
canvas.setHeight(590);

fabric.Image.fromURL('assets/img/materials/marble.bmp', function(image) {
    image.set({
        // I need this because the image size and the canvas size could be different
        // in this way the image always covers the canvas
        width:660,
        height:590
    });

    canvas.setBackgroundImage(image);
});

canvas.renderAll();

The canvas is created, but the background image doesn't appear unless I click inside the canvas, as I click inside the canvas the background appears.

I'm working on my local machine and the application will not be published online.

Why do you think that I'm having this problem? Am I doing anything wrong? How could I fix this behaviour?

• javascript
• canvas
• fabricjs

Share Improve this question Follow asked Feb 6, 2016 at 14:56 Luigi CaradonnaLuigi Caradonna 1,06422 gold badges1515 silver badges3333 bronze badges 4

• 1 Try calling canvas.renderAll() in the callback function(image) - fabric.Image.fromURL is likely loading the image asynchronously, so the bottom line of of your code runs before the image is loaded. – Kenney Commented Feb 6, 2016 at 15:04
• Thank you, that works. As ment I can't set your answer as the correct one. – Luigi Caradonna Commented Feb 6, 2016 at 15:14
• You're wele! That's allright - there's gazillions questions like this; it's probably going to be marked a duplicate by someone who can find the best answer to link to ;-) – Kenney Commented Feb 6, 2016 at 15:16
• FYI, this issue pertains to image objects too (not just background images). The below solution using canvas.renderAll() within callback seems to work. – Kalnode Commented Sep 7, 2021 at 15:23

Add a ment  | 

2 Answers 2

Sorted by: Reset to default 5

fabric.image.fromURL is asyncronous. You have to call the renderAll() inside the callback if you want to show the backgroundimage asap.

Otherwise your mouse click will trigger a renderAll some fraction of second after the load is finished and the background will be rendered.

canvas = new fabric.Canvas('canvas');
canvas.setWidth(660);
canvas.setHeight(590);

    fabric.Image.fromURL('assets/img/materials/marble.bmp', function(image) {
        image.set({
            // I need this because the image size and the canvas size could be different
            // in this way the image always covers the canvas
            width:660,
            height:590
        });

        canvas.setBackgroundImage(image);
        canvas.renderAll();
    });

In my case, Safari iOS would not render the background ~20-60% of the time (version "fabric": "^4.3.1"). Waiting did not resolve. Tapping the canvas would activate/render the background. Adding renderAll() in various places did not resolve it for me. Did not happen on Chrome, only Safari iOS (ver. 14.1 at the time)

B64 workaround:

Dropping the fabric.Image.fromURL and instead providing a b64 image to setBackgroundImage worked for me consistently with all browsers.

let myImg = `data:image/jpeg;charset=utf-8;base64,<- base64 data->`

this.canvasObj.setBackgroundImage(
  myImg, //b64
  this.canvasObj.renderAll.bind(this.canvasObj)
);

本文标签： javascriptFabricjs background appears only after clickStack Overflow