Rotate Image on Itself With Matrix Object?

Dan

15y4.8kGDI+

Hi guys,

I hope you can help?

I'm trying to rotate a circle graphically in C# so that it just spins round (with no movement side to side or up or down) just like a wheel does.

I'm using the Matrix.Rotate(), Matrix.Translate() and Graphics.Transform() methods. I can get the object to rotate no problem but not so that it stays in one place & rotates on itself. I think it's probably just a case of getting the correct parameters for the Matrix.Translate() method. My best guess for it so far is below:

(It's a try at using the Rectangle object I used to create my Ellipse drawing to try & centre the rotation)

matrix1.Translate((float)rectangle1.Width / 2, (float)rectangle1.Height / 2);

I understand well all the basics about Graphics, Image, Bitmap, Rectangle and Brush objects etc and their associated methods. However, if honest, the Matrix class & various Rotation & Transform methods are new to me. I've been searching the web & feel like I've tried everything without success.

Below is an abbreviation of my best code so far. It rotates the image but not on itself. Any help is very much appreciated:

(Note: I've tried the simpler Graphics.TranslateTransform() and Graphics. RotateTransform() but unfortunately these don't seem to work with the Graphics.FillEllipse() method)

public Form1()

{

InitializeComponent();

CreateCircleSupportElements();

}

Graphics graphics1;

Image image1;

Brush brush1;

Rectangle rectangle1;

Matrix matrix1;

private void Form1_Paint(object sender, PaintEventArgs e)

{

graphics1 = e.Graphics;

graphics1.Transform = matrix1;

graphics1.FillEllipse(brush1, rectangle1);

}

private void CreateCircleSupportElements()

{

image1 = Image.FromFile(@"C:\APicture.jpg");

brush1 = new TextureBrush(image1);

rectangle1 = new Rectangle(100, 100, 100, 100);

matrix1 = new Matrix();

}

private void button1_Click(object sender, EventArgs e)

{

matrix1.Translate((float)rectangle1.Width / 2, (float)rectangle1.Height / 2);

matrix1.Rotate(5);

this.Invalidate();

}

Thank you,

Dan.

3 Replies

Know the answer? Post it — somebody with the same question will find it here.

Dan15y ago
Hi Sascha,

Yes, that worked brilliantly : )

Thanks very much again.

Just for anyone's info, for my own use, I basically combined the code very kindly provided by Sacha, with the principles found in the example at:

http://www.dreamincode.net/code/snippet2640.htm

Thanks again,

Dan :)
Dan15y ago
Thanks Sascha,

Just to let you know, I'm in the process of checking that out and I'll let you know how I got on.

Thanks very much indeed for taking the time to reply. I very much appreciate it : )

Regards,

Dan : )
Sascha B15y ago
I made something like this in my programm

//- First rotate the matrix
   Matrix matrix = new Matrix();
   matrix.Translate(0, 0);
   matrix.RotateAt((float)22.5, new PointF(w / 2, h / 2)); // here you can specifiy a point (in your case the middle) it is rotated by 22,5°
// then assign the drawn grafik to the matrix
   bmpgrafik.Transform = matrix;
// then everything that is draw will be rotated by 22,5°
   float x0 = w / 2, y0 = h / 2, x1, y1;
   for (double i = 1; i < 8; i++)
   {
   double winkel1 = Math.PI / 2 - i * 2 * Math.PI / 8;
   x1 = (float)(x0 + w * 1 * Math.Cos(winkel1));
   y1 = (float)(y0 - w * 1 * Math.Sin(winkel1));

   bmpgrafik.DrawLine(new Pen(Color.FromArgb(50, Color.Black)), x1, y1, w - x1, h - y1);
   }
// try it out :)