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How to Get Image Mask In Canvas?

3 minutes read

To get an image mask in canvas, you can create a new canvas element and draw the image you want to use as the mask on this new canvas. Then, you can use the globalCompositeOperation property of the canvas context to set the source-in or source-atop mode, which will allow you to apply the mask to another image by drawing it on top of the masked image. Finally, you can draw the masked image on the main canvas to display the result.


How to create a circular image mask in canvas?

To create a circular image mask in canvas, you can follow these steps:

  1. Create a canvas element in your HTML:
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<canvas id="canvas" width="200" height="200"></canvas>


  1. Get the canvas context and load the image you want to use:
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const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');

const img = new Image();
img.onload = function() {
  ctx.drawImage(img, 0, 0, canvas.width, canvas.height);
}
img.src = 'image.jpg';


  1. Create a circular clipping path using the arc method:
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ctx.beginPath();
ctx.arc(canvas.width / 2, canvas.height / 2, canvas.width / 2, 0, Math.PI * 2);
ctx.clip();


  1. Draw the image within the circular clipping path:
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ctx.drawImage(img, 0, 0, canvas.width, canvas.height);


  1. Clear the clipping path to reset for future drawings:
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ctx.restore();


Your image should now be displayed within a circular mask on the canvas.


How to add transparency to an image mask in canvas?

To add transparency to an image mask in canvas, you can use the globalCompositeOperation property and set it to 'destination-out'. This will draw the image mask, but only where the mask is not transparent.


Here's an example code snippet to demonstrate how to add transparency to an image mask in canvas:

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<!DOCTYPE html>
<html>
<head>
    <title>Image Mask Transparency</title>
</head>
<body>
    <canvas id="myCanvas" width="400" height="400"></canvas>

    <script>
        const canvas = document.getElementById('myCanvas');
        const ctx = canvas.getContext('2d');

        // Load the image mask
        const img = new Image();
        img.src = 'image-mask.png';
        img.onload = () => {
            // Draw the image mask
            ctx.drawImage(img, 0, 0, canvas.width, canvas.height);

            // Add transparency to the image mask
            ctx.globalCompositeOperation = 'destination-out';
            ctx.fillStyle = 'rgba(0, 0, 0, 0.5)';
            ctx.fillRect(0, 0, canvas.width, canvas.height);
        };
    </script>
</body>
</html>


In this code snippet, we first load the image mask using the Image() constructor and draw it on the canvas using ctx.drawImage(). Then, we set the globalCompositeOperation to 'destination-out' to add transparency to the image mask. Finally, we fill a rectangle with a semi-transparent color using ctx.fillRect() to make the mask partially transparent.


You can adjust the opacity of the transparency by changing the alpha value in the rgba() function (e.g., 'rgba(0, 0, 0, 0.5)' for 50% opacity).


What is the effect of applying multiple image masks in canvas?

When multiple image masks are applied on a canvas, the resulting effect is a composite of all the masks. Each mask will contribute to determining which parts of the image are visible and which are hidden.


For example, if you have a canvas with an image and apply two different masks, one circular and one rectangular, the final image will be a combination of the two masks. The areas where both masks overlap will be fully visible, while the areas where only one mask overlaps will be partially visible or hidden depending on the opacity of the masks.


Overall, applying multiple image masks allows for complex and creative effects to be achieved on an image in a canvas.

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