Returns the diagonal screen size in inches

display_get_diagonal_inches.gml

/**
 * Calculates the diagonal length of the display in inches based on the display's width, height, and DPI values.
 *
 * @returns {number} The diagonal length of the display in inches.
 */
 
function display_get_diagonal_inches()
{
   	return sqrt(sqr(display_get_width()) + sqr(display_get_height())) / max(display_get_dpi_x(), display_get_dpi_y());
}