Find corners of a rotated rectangle

Question

I'm trying to resize a rotated rectangle, you just drag the image out (or in) from 1 corner, and the corner diagonal of that 1 will stay in the old position.

So I know the angle(radians) of rotation and 2 corners diagonal of each other, now I would like to find the other two corners.

I've tried to calculate em with Trigonometry but I failed miserably, so how can u calculate those other 2 points.

oh, forgot to mention that the image is rotated around the top left corner — user1232990, Feb 26 '12 at 10:53

score 0 · Accepted Answer · answered Feb 26 '12 at 04:08

0

In pseudocode:

r = (x2 - x1)*sin(a) - (y2 - y1)*cos(a)
x3 = x1 + r*sin(a)
y3 = y1 - r*cos(a)
x4 = x2 - r*sin(a)
y4 = y2 + r*cos(a)

What this is doing is recovering the length r of the side of the rotated rectangle, then using that length to calculate where the two other points should be, relative to the two points that you have already.

answered Feb 26 '12 at 04:08

Emilio Silva

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I tried to implement this but failed,http://stackoverflow.com/questions/9454278/canvas-image-editor – user1232990 Feb 27 '12 at 00:36

Find corners of a rotated rectangle

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