Question

If I have these rules:

width:50px;
height:100px;
-moz-transform: rotate(0deg)

and then an event changes the transform to:

-moz-transform: rotate(90deg)

logically, shouldn’t that automatically exchange the width and the height? I need the rotate to switch width and height for accurate position detection.

Thanks,

Joe

Answer 1

It seems like the transform is applied after everything else, so the width and height aren’t updated. The best solution I can think of is to calculate the rotated dimensions yourself, using the rotation matrix:

[ cos X     -sin X ] [ width  ]
[ sin X      cos X ] [ height ]

It’s straightforward to translate this into JavaScript. You need to rotate all four corners (0,0) (w,0) (0,h) (w,h) and then the rotated dimensions are the width and height of the rotated bounding rectangle.

var angle = angle_in_degrees * Math.PI / 180,
    sin   = Math.sin(angle),
    cos   = Math.cos(angle);

// (0,0) stays as (0, 0)

// (w,0) rotation
var x1 = cos * width,
    y1 = sin * width;

// (0,h) rotation
var x2 = -sin * height,
    y2 = cos * height;

// (w,h) rotation
var x3 = cos * width - sin * height,
    y3 = sin * width + cos * height;

var minX = Math.min(0, x1, x2, x3),
    maxX = Math.max(0, x1, x2, x3),
    minY = Math.min(0, y1, y2, y3),
    maxY = Math.max(0, y1, y2, y3);

var rotatedWidth  = maxX - minX,
    rotatedHeight = maxY - minY;