Canvas Images
Let’s have some knowledge of the canvas images by understanding its function for drawing the images. To draw a canvas image, the drawImage() method is used that requires an images object and a destination point. The destination point means the top-left corner of the images relative to the top-left corner of the canvas on which the image is to be drawn.
There are the following three variants of this method.
- drawImage(image, dx, dy).
- drawImage(image, dx, dy, dw, dh)
- drawImage(image, sx, sy, sw, sh, dx, dy, dw, dh,).
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First we should know about all the parameters given in the methods, so we can understand the use of all the parameters and can easily play with the images.
The parameter "images" is the image that is to be drawn.
The parameters "dx" and "dy" are known as "destinationX" and "destinationY" respectively and determine where the image is to be drawn on the canvas.
The parameters "dw" and "dh" are known as "destinationWidth" and "destinationHeight" respectively and determine the scale size of the image.
The parameters "sx" and "sy" are known as "sourceX" and "sourceY" respectively and determine the where in the source images to start copying the rectangle of the images onto the canvas.
The parameters "sw" and "sh" are known as "sourceWidth" and "sourceHeight" respectively and determine the scaling (extent of copying of width and height) of the source image.
As we all know, the drawImage() method needs an object, so first we should create an image object and should wait for it to load by applying the window.onload() function before the initiation of the drawImages() method.
Now let’s move to see the example of first variant, imageDraw(image, dx, dy).
Example : Drawing and loading
- <html>
- <body>
- <p>Image being used:</p>
- <img id="skullash" width="250" height="210"
- src="C:\Users\dddd\Desktop\cigarette-smoke-skull.jpg" alt="The Skull Ash">
- <p>Canvas Image:</p>
- <canvas id="smokeCanvas" width="325" height="225"
- style="border:3px solid red;">
- < script > window.onload = function ashSkull() {
- var newCanvas = document.getElementById("smokeCanvas");
- var context = newCanvas.getContext("2d");
- var image = document.getElementById("skullash");
- context.drawImage(image, 0, 0);
- }
- </script>
- </canvas>
- </body>
- </html>
Output
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We can observe the image drawn on the canvas (with a Red border).
Next we are going to discuss the second variant as in the following:
- drawImage(image, dx, dy, dw, dh)
Here we will change the image and the method in JavaScript for scaling the image.
- context.drawImage(image, 90, 60, 180, 150);
Here is the output after scaling.
Output
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We can see the scale size and the position of the image onto the canvas.
Now to draw the section of the image using the next variant method as in the following:
- drawImage(image, sx, sy, sw, sh, dx, dy, dw, dh,)
By changing the method in JavaScript:
- context.drawImage(image, 90, 90, 130, 110, 0, 0, 250, 200);
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Another section by:
- context.drawImage(image, 0, 0, 100, 250, 70, 70, 200, 180);
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The preceding output is the two different sections of the given image with its scale size as well as position of the image on the canvas.
Thank you, keep learning and sharing.