Alternative to Graphics.ScaleTransform

Question

I am doing custom drawing using the GDI+.

Normally if I want to fit whatever I am drawing to the window, I calculate the appropriate ratio and I ScaleTransform everything by that ratio:

e.Graphics.ScaleTransform(ratio, ratio);

The problem with ScaleTransform is that it scales everything including pen strokes and brushes.

Hoe do I scale all of the pixel coordinates of what I'm drawing? Every line, rectangle, or path is basically a series of points. So I can multiply all of those points by the ratio manually, but is there an easy alternative to do this more seamlessly?

Answer 1

Try putting all your objects in a GraphicsPath instance first. It doesn't have a ScaleTransform method but you can transform the objects with GraphicsPath.Transform. You can pass a scaling matrix via Matrix.Scale.

Answer 2

You can wrap the GDI graphics object and store the scale factor

interface IDrawing
{
   void Scale(float sx, float sy);
   void Translate(float dx, float dy);
   void SetPen(Color col, float thickness);
   void DrawLine(Point from, Point to);
   // ... more methods
}

class GdiPlusDrawing : IDrawing
{
   private float scale;
   private Graphics graphics;
   private Pen pen;

   public GdiPlusDrawing(Graphics g)
   {
      float scale = 1.0f;
   }

   public void Scale(float s)
   {
       scale *= s;
       graphics.ScaleTransform(s,s);
   }

   public void SetPen(Color color, float thickness)
   {
       // Use scale to compensate pen thickness.
       float penThickness = thickness/scale;
       pen = new Pen(color, penThickness);   // Note, need to dispose.
   }

   // Implement rest of IDrawing
}