In the course of toying with SVG for the first time (using the Raphael library), I've run into a problem positioning dynamic elements on the canvas in such a way that they're completely contained within the canvas. What I'm trying to do is randomly position n words/short phrases.

Since the text is variable, its position needs to be variable as well so what I'm doing is:

1. Initially creating the text at point 0,0 with no opacity.
2. Checking the width of the drawn text element using text.getBBox().width.
3. Setting a new x coordinate as Math.random() * (canvas_width - ( text_width/2 ) - pad).
4. Altering the x coordinate of the text to the newly set value (text.attr( 'x', x ) ).
5. Setting the opacity attribute of the text to 1.

I'll be the first to admit that my math acumen is limited, but this seems pretty straightforward. Somehow, I still end up with text running off beyond the right edge of my canvas. For simplicity above, I removed the bit that also sets a minimum x value by adding it to the Math.random() result. It is there, though, and I see the same problem on the leading edge of the canvas.

My understanding (such as it is), is that the Math.random() bits would generate a number between 0 and 1 which could then be multiplied by some number (in my case, the canvas width - half of the text width - some arbitrary padding) to get the outer bound. I'm dividing the width of the text in half because its position on the grid is set at its center.

I hope I've just been staring at this for too long, but is my math that rusty or am I misunderstanding something about the behavior of Math.random(), SVG, text or anything else that's under the hood of this solution?