Rotate

Hi all, first let me say that I'm a huge fan of this website I scan it's tutorial section on a dailey bases and I have found it to be of great help to me. But I'm stuck on a certain problem using the gdi+ graphics class. In c#, I have drawn a figure using a graphicsPath, now when I want to rotate this figure, it does this using 0,0 as the pivoting point. But this is not what I would like, I would like to set the pivot point to the center of the figure. I have googled and found a few articles about this but none of these I understand fully.

What you want to do is use the RotateAt method in the graphics path using a Matrix object. The subject of the Matrix object is too complex to get into but believe me it works. Here some sample code that will illustrate the "RotateAt" method. First create a 300x300 form. Switch to code view and paste this code: Good Luck!

GraphicsPath gp = null;

Matrix myRotateMatrix = null;

protected override void OnPaintBackground(PaintEventArgs e)
{
e.Graphics.Clear(Color.White);

//ensure the graphicsPath object is created
if (gp == null) CreateGraphicsPathObject();

//draw the gp object
e.Graphics.FillPath(Brushes.Blue, gp);

}

private void btnRotate_Click(object sender, EventArgs e)

{

//transform (in this case the transformation is a rotation) the
//graphics path object by the amount specified by myRotateMatrix
gp.Transform(myRotateMatrix);

//Tell the Form that it needs to repaint itself
this.Invalidate();

}

private void CreateGraphicsPathObject()

{

gp = new GraphicsPath();

StringFormat sf = new StringFormat();
sf.Alignment = StringAlignment.Near;
gp.AddString("Click To Rotate Me!", this.Font.FontFamily, 1, 20, new Point(50, 100), sf);

//Since we are creating the GraphicsPath object
//we need to initialze our matrix object that will
//control the rotation
myRotateMatrix = new Matrix();

PointF myCenterPoint = gp.GetBounds().Location;
myCenterPoint.X = myCenterPoint.X + gp.GetBounds().Width / 2;
myCenterPoint.Y = myCenterPoint.Y + gp.GetBounds().Height / 2;

myRotateMatrix.RotateAt(20F, myCenterPoint);

}

2 Replies

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Edwin Blommaerts19y ago
Great, that's just what I needed to know, thanks a lot.
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Richard Blythe19y ago
What you want to do is use the RotateAt method in the graphics path using a Matrix object. The subject of the Matrix object is too complex to get into but believe me it works. Here some sample code that will illustrate the "RotateAt" method. First create a 300x300 form. Switch to code view and paste this code: Good Luck!

GraphicsPath gp = null;

Matrix myRotateMatrix = null;

protected override void OnPaintBackground(PaintEventArgs e)
{
e.Graphics.Clear(Color.White);

//ensure the graphicsPath object is created
if (gp == null) CreateGraphicsPathObject();

//draw the gp object
e.Graphics.FillPath(Brushes.Blue, gp);

}

private void btnRotate_Click(object sender, EventArgs e)

{

//transform (in this case the transformation is a rotation) the
//graphics path object by the amount specified by myRotateMatrix
gp.Transform(myRotateMatrix);

//Tell the Form that it needs to repaint itself
this.Invalidate();

}

private void CreateGraphicsPathObject()

{

gp = new GraphicsPath();

StringFormat sf = new StringFormat();
sf.Alignment = StringAlignment.Near;
gp.AddString("Click To Rotate Me!", this.Font.FontFamily, 1, 20, new Point(50, 100), sf);

//Since we are creating the GraphicsPath object
//we need to initialze our matrix object that will
//control the rotation
myRotateMatrix = new Matrix();

PointF myCenterPoint = gp.GetBounds().Location;
myCenterPoint.X = myCenterPoint.X + gp.GetBounds().Width / 2;
myCenterPoint.Y = myCenterPoint.Y + gp.GetBounds().Height / 2;

myRotateMatrix.RotateAt(20F, myCenterPoint);

}

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