I developing a HTML5 Canvas App and it involves reading a xml file that describes the position of arrows, rectanges and other shapes I need to to draw on the canvas.
Example of the XML layout:
<arrow left="10" top="20" width="100" height="200" rotation="-40" background-color="red"/>
<rect left="10" top="20" width="100" height="200" rotation="300" background-color="red"/>
If the object is rotated it involves calculating the position of a point(called P the new position of the object after rotation) when rotated around another point(left,top). I am attempting to come up with a general function/formula I can use to calculate this point P but my Maths is a little weak & I cannot identify what arc/tangent formula I am meant to use.
Can you assist me to come up with a formula I can use to calculate point P for rotations that can be both positive & negative?
In the above example: point(14,446) is the left,top point & point(226,496) is the mid point of the object when NOT rotated so the point=(left+width/2,top+height/2) and the blue dot is the mid point when rotated. I know how to calulate the length of the line between points (14,446) & (226,496) but not how to calculate the blue point x,y position - BTW: the length of this line is the same as the line between the blue point & (14,446)
len = sqrt( (496-446)^2 + (226-14)^2 );
= 227.56;