Why Do CSS and HTML Attributes Produce Different Canvas Sizes?

Canvas Size Discrepancy in CSS vs. Element Attributes

When using HTML5 canvas, you may encounter different results depending on whether you set the size using CSS or element attributes. This discrepancy arises because CSS scales the canvas as if it were zoomed in, while element attributes determine the actual drawable area.

To illustrate, consider the following code:

<style>
#canvas {
    width: 800px;
    height: 600px;
}
</style>
<canvas>

This code will create a canvas that appears to be 800x600 pixels on the screen. However, the actual drawable area is only 300x150 pixels, as per the default canvas element dimensions in the HTML specification.

In contrast, the following code:

<canvas>

will create a canvas with an actual drawable area of 800x600 pixels. This is because the width and height attributes dictate the number of pixels available for drawing.

The distinction is important because CSS can distort the canvas if the display size and the actual size differ. For example, if you specify a canvas size of 32x32 pixels but set the CSS size to 800x16px, the browser will stretch and squash the canvas to fit the display. This can compromise the quality of any drawings or graphics rendered on the canvas.

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