Global, Local, and Composite Transformations

Transformations can be divided into two categories based on their scope: global and local. In addition, there are composite transformations. A global transformation is applicable to all items of a Graphics object. The Transform property of the Graphics class is used to set global transformations.

A composite transformation is a sequence of transformations. For example, scaling followed by translation and rotation is a composite translation. The MultiplyTransform, RotateTransform, ScaleTransform, and TranslateTransform methods are used to generate composite transformations.

Listing 10.14 draws two ellipses and a rectangle, then calls ScaleTransform, TranslateTransform, and RotateTransform (a composite transformation). The items are drawn again after the composite transformation.

Listing 10.14 Applying a composite transformation

private void GlobalTransformation_Click(object sender, System.EventArgs e) { // Create a Graphics object Graphics g = this.CreateGraphics(); g.Clear(this.BackColor); // Create a blue pen with width of 2 Pen bluePen = new Pen(Color.Blue, 2); Point pt1 = new Point(10, 10); Point pt2 = new Point(20, 20); Color [] lnColors = {Color.Black, Color.Red}; Rectangle rect1 = new Rectangle(10, 10, 15, 15); // Create two linear gradient brushes LinearGradientBrush lgBrush1 = new LinearGradientBrush (rect1, Color.Blue, Color.Green, LinearGradientMode.BackwardDiagonal); LinearGradientBrush lgBrush = new LinearGradientBrush (pt1, pt2, Color.Red, Color.Green); // Set linear colors lgBrush.LinearColors = lnColors; // Set gamma correction lgBrush.GammaCorrection = true; // Fill and draw rectangle and ellipses g.FillRectangle(lgBrush, 150, 0, 50, 100); g.DrawEllipse(bluePen, 0, 0, 100, 50); g.FillEllipse(lgBrush1, 300, 0, 100, 100); // Apply scale transformation g.ScaleTransform(1, 0.5f); // Apply translate transformation g.TranslateTransform(50, 0, MatrixOrder.Append); // Apply rotate transformation g.RotateTransform(30.0f, MatrixOrder.Append); // Fill ellipse g.FillEllipse(lgBrush1, 300, 0, 100, 100); // Rotate again g.RotateTransform(15.0f, MatrixOrder.Append); // Fill rectangle g.FillRectangle(lgBrush, 150, 0, 50, 100); // Rotate again g.RotateTransform(15.0f, MatrixOrder.Append); // Draw ellipse g.DrawEllipse(bluePen, 0, 0, 100, 50); // Dispose of objects lgBrush1.Dispose(); lgBrush.Dispose(); bluePen.Dispose(); g.Dispose(); }

Figure 10.15 shows the output from Listing 10.14.

Figure 10.15. Composite transformation

A local transformation is applicable to only a specific item of a Graphics object. The best example of local transformation is transforming a graphics path. The Translate method of the GraphicsPath class translates only the items of a graphics path. Listing 10.15 translates a graphics path. We create a Matrix object and apply rotate and translate transformations to it.

Listing 10.15 Translating graphics path items

private void LocalTransformation_Click(object sender, System.EventArgs e) { // Create a Graphics object Graphics g = this.CreateGraphics(); g.Clear(this.BackColor); // Create a GraphicsPath object GraphicsPath path = new GraphicsPath(); // Add an ellipse and a line to the // graphics path path.AddEllipse(50, 50, 100, 150); path.AddLine(20, 20, 200, 20); // Create a blue pen with a width of 2 Pen bluePen = new Pen(Color.Blue, 2); // Create a Matrix object Matrix X = new Matrix(); // Rotate 30 degrees X.Rotate(30); // Translate with 50 offset in x direction X.Translate(50.0f, 0); // Apply transformation on the path path.Transform(X); // Draw a rectangle, a line, and the path g.DrawRectangle(Pens.Green, 200, 50, 100, 100); g.DrawLine(Pens.Green, 30, 20, 200, 20); g.DrawPath(bluePen, path); // Dispose of objects bluePen.Dispose(); path.Dispose(); g.Dispose(); }

Figure 10.16 shows the output from Listing 10.15. The transformation affects only graphics path items (the ellipse and the blue [dark] line).

Figure 10.16. Local transformation