[gameprogrammer] Re: Constraining a line to a rectangle

["Alan Wolfe" <atrix2@cox.net>]

I think your best solution is what you were saying, test the line against
each of the edges of the rectangle.

finding out if you should set a or b to the intersected point is as easy as
seeing which side is on the inside of the edge.

if your testing the right edge and the lines intersect, you set the line's
point that has a higher X value to the intersection point.

that oughta work shouldnt it?

----- Original Message ----- 
From: "Kevin Jenkins" <gameprogrammer@rakkar.org>
To: <gameprogrammer@freelists.org>
Sent: Monday, April 12, 2004 9:35 PM
Subject: [gameprogrammer] Constraining a line to a rectangle


> In my game I have a series of lines.  For each line, it is possible that
one
> or both of the endpoints is outside the viewport, which is smaller than
the
> screen.  Given the endpoints of the line, I want to modify these endpoints
> so I when I render a line between the two endpoints, all rendering is done
> inside the viewport.
>
> I want to write a function that takes the following parameters:
> Point A by reference.  As input, one of the endpoints of the line.  As
> output, the modified endpoint.
> Point B by reference.  As input, one of the endpoints of the line.  As
> output, the modified endpoint.
> Viewport upper left coordinate
> Viewport lower right coordinate.
>
> The function should modify point A and point B such that when a line is
> drawn from A to B, the line is only drawn within the viewport.
>
> My initial thought as to the solution is to solve for line intersection
for
> each of the 4 edges of the viewport.  If the line intersects the edge of
the
> viewport, then set the endpoint of the line at that point.  Of course
there
> are still annoying issues, such as that I don't know whether to set Point
A
> or Point B to the point of intersection.
>
> While I can brute force it, I think there must be a much simpler and more
> elegant solution.
>
> Ideas?
>
>