Question

so i have drawn a few objects , circles squares or even lines. This is the code i use to draw the images:

Graphics surface = this.splitContainer1.Panel2.CreateGraphics();
Pen pen1 = new Pen(ColorR.BackColor, float.Parse(boxWidth.Text));

switch (currentObject)
{
case "line":
    if (step == 1)
    {
        splitContainer1.Panel2.Focus();
        one.X = e.X;
        one.Y = e.Y;
        boxX.Text = one.X.ToString();
        boxY.Text = one.Y.ToString();
        step = 2;
    }
    else
    {
        two.X = e.X;
        two.Y = e.Y;
        boxX2.Text = two.X.ToString();
        boxY2.Text = two.Y.ToString();
        surface.DrawLine(pen1, one, two);
        step = 1;
    }
    break;

case "circle":
    if (step == 1)
    {
        boxX.Text = e.X.ToString();
        boxY.Text = e.Y.ToString();
        step = 2;
    }
    else
    {
        int tempX = int.Parse(boxX.Text);
        int tempY = int.Parse(boxY.Text);
        int tempX2 = e.X;
        int tempY2 = e.Y;
        int sideX, sideY;
        if (tempX > tempX2)
        {
            sideX = tempX - tempX2;
        }
        else
        {
            sideX = tempX2 - tempX;
        }

        if (tempY > tempY2)
        {
            sideY = tempY - tempY2;
        }
        else
        {
            sideY = tempY2 - tempY;
        }

        double tempRadius;
        tempRadius = Math.Sqrt(sideX * sideX + sideY * sideY);
        tempRadius *= 2;

        bWidth.Text = bHeight.Text = Convert.ToInt32(tempRadius).ToString();

        surface.DrawEllipse(
           pen1,
           int.Parse(boxX.Text) - int.Parse(bWidth.Text) / 2, 
           int.Parse(boxY.Text) - int.Parse(bHeight.Text) / 2,
           float.Parse(bWidth.Text), float.Parse(bHeight.Text));
        step = 1;
    }
    break;

case "square":
    if (step == 1)
    {
        boxX.Text = e.X.ToString();
        boxY.Text = e.Y.ToString();
        step = 2;
    }
    else if (step == 2)
    {
        int tempX = e.X;
        if (tempX > int.Parse(boxX.Text))
        {
            bWidth.Text = (tempX - int.Parse(boxX.Text)).ToString();
        }
        else
        {
            bWidth.Text = (int.Parse(boxX.Text) - tempX).ToString();
        }

        step = 3;
    }
    else
    {
        int tempY = e.Y;
        if (tempY > int.Parse(boxY.Text))
        {
            bHeight.Text = (tempY - int.Parse(boxY.Text)).ToString();
        }
        else
        {
            bHeight.Text = (int.Parse(boxY.Text) - tempY).ToString();
        }

        surface.DrawRectangle(
            pen1,
            int.Parse(boxX.Text),
            int.Parse(boxY.Text),
            int.Parse(bWidth.Text),
            int.Parse(bHeight.Text));
        step = 1;
    }

    break;
}

So after I draw the images, I want to be able to select a figure and–for example–change the color or rotate it. But I cant seem to figure it out how to do it.

Answer 1

I suggest defining a base abstract shape class that has methods all shapes should provide, such as a method to draw itself on a graphics object, a method that says whether a point is within it / should could as selecting it, a method to rotate it by a given amount and a method to change the color.

Once you’ve got your shape class then you’ve got to work out how to fill in the methods for each derived shape. For drawing you’ve already got the code. For selecting it, that will be dependent on the shape. For something like a circle it’s fairly easy, just calculate the distance between the center of the circle, and the point clicked, for something like a line it’s harder as you don’t want the user to have to click it exactly.

That leaves rotating and changing the colour. Changing the colour is easy, just have a Color property on the Shape class, then when you draw your shapes, use that colour to create a brush or pen.

As for rotation, take a look at Graphics.RotateTransform.

---

public abstract class Shape
{
    public Color Color { get; set; }
    public float Rotation { get; set; }
    public Point Position { get; set; }

    public Shape(Color color, float rotation, Point position)
    {
        Color = color;
        Rotation = rotation;
        Position = position;
    }

    public void ChangeRotation(float amount)
    {
        Rotation += amount;
    }

    public abstract void Draw(Graphics graphics);
    public abstract bool WithinBounds(Point point);
}

public class Circle : Shape
{
    public float Radius { get; set; }

    public Circle(Color color, float rotation, Point position)
        :base(color, rotation, position)
    {

    }

    public override void Draw(Graphics graphics)
    {

    }

    public override bool WithinBounds(Point point)
    {
        if (Math.Sqrt(Math.Pow(point.X - Position.X, 2) + Math.Pow(point.Y - Position.Y, 2)) <= Radius)
            return true;
        else
            return false;

        // Note, if statement could be removed to become the below:
        //return Math.Sqrt(Math.Pow(point.X - Position.X, 2) + Math.Pow(point.Y - Position.Y, 2)) <= Radius;
    }
}