CODEWITHSUNDEEP
c#mathrotationangle
James
James

Reputation: 3625

Rotate a point by another point in 2D

I want to know how to work out the new co-ordinates for a point when rotated by an angle relative to another point.

I have a block arrow and want to rotate it by an angle theta relative to a point in the middle of the base of the arrow.

This is required to allow me to draw a polygon between 2 onscreen controls. I can't use and rotate an image.

From what I have considered so far what complicates the matter further is that the origin of a screen is in the top left hand corner.

Upvotes: 56

Views: 55237

Answers (4)

Spinstaz
Spinstaz

Reputation: 331

This takes a layout transform command on your image in the WPF, and rotates it the degree you want.

progress_image.LayoutTransform = new RotateTransform(90);

Upvotes: 0

thumbmunkeys
thumbmunkeys

Reputation: 20764

If you have the System.Windows.Media namespace available, then you can use the built in transformations:

    using System.Windows.Media;

    var transform = new RotateTransform() {Angle = angleInDegrees, CenterX = center.X, CenterY = center.Y};
    var transformedPoint = transform.Transform(point);

Upvotes: 2

Sophie Alpert
Sophie Alpert

Reputation: 143204

If you rotate point (px, py) around point (ox, oy) by angle theta you'll get:

p'x = cos(theta) * (px-ox) - sin(theta) * (py-oy) + ox
p'y = sin(theta) * (px-ox) + cos(theta) * (py-oy) + oy

Upvotes: 138

Mehrdad Afshari
Mehrdad Afshari

Reputation: 422172

If you are using GDI+ to do that, you can use Transform methods of the Graphics object:

graphics.TranslateTransform(point of origin);
graphics.RotateTransform(rotation angle);

Then draw the actual stuff.

Upvotes: 7

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