function get_brush_canvas_size(brush_size, brush_shape) {
	// brush_shape optional, only matters if it's circle
	// @TODO: does it actually still matter? the ellipse drawing code has changed

	// round to nearest even number in order for the canvas to be drawn centered at a point reasonably
	return Math.ceil(brush_size * (brush_shape === "circle" ? 2.1 : 1) / 2) * 2;
}
Calculates the canvas size required for a brush based on the brush size and shape.

@param {number} brush_size - The size of the brush.
@param {BrushShape} [brush_shape] - The shape of the brush.
@returns {number} The canvas width/height required for the brush.