Why Do CSS and Element Attributes Produce Different HTML5 Canvas Sizes?

Size of HTML5 Canvas Discrepancy: CSS vs. Element Attributes

When setting the size of an HTML5 canvas, you may encounter unexpected results depending on whether you use CSS or element attributes.

Observed Difference:

The following code snippets produce different canvas sizes:

<!-- Using CSS -->
<style>
#canvas {
    width: 800px;
    height: 600px;
}
</style>
<canvas></canvas>

Explanation:

This difference arises from the distinct roles of CSS and element attributes.

• CSS properties (width, height): Control the visual size of the element on the screen, scaling it up or down as specified. However, the actual number of pixels available for drawing on the canvas is not affected.
• Element attributes (width, height): Determine the physical size of the canvas itself, establishing the number of pixels that can be drawn upon. If these attributes are not set, the default dimensions are 300px by 150px.

Example:

Consider an image with actual dimensions of 32x32 pixels. If you use CSS to display it with dimensions of 800px by 16px, the browser must stretch or compress the image to fit the specified size. The same principle applies to HTML Canvas.

When using CSS dimensions that differ from the actual canvas size, the browser scales the canvas for display. This can result in pixel distortion or unintended behavior. Therefore, it is recommended to set both the CSS properties and element attributes to match the desired canvas dimensions to ensure accurate rendering.

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