CODEWITHSUNDEEP
c#winformsdrawpictureboxlines
Matimont
Matimont

Reputation: 759

Draw line in picturebox and redraw on zoom

I'm drawing a line in a picturebox this way:

horizontalstart = new Point(0, e.Y); //Start point of Horizontal line.
horizontalend = new Point(picbox_mpr.Width, e.Y); //End point of Horizontal line.
verticalstart = new Point(e.X, 0); //Start point of Vertical line
verticalend = new Point(e.X, picbox_mpr.Height); //End point of Vertical line.

Then on the paint event I do this:

e.Graphics.DrawLine(redline, horizontalstart, horizontalend); //Draw Horizontal line.
e.Graphics.DrawLine(redline, verticalstart, verticalend); //Draw Vertical line.

Pretty simple, now, my image can zoom and here's where I struggle..

How do I keep the line in the same spot that was drawn even if I zoom the image?

Upvotes: 0

Views: 2454

Answers (1)

Idle_Mind
Idle_Mind

Reputation: 39122

Instead of storing an absolute integer coordinate, store a decimal value representing the "percentage" of that coord with respect to the width/height of the image. So if the X value was 10 and the width was 100, you store 0.1. Let's say the image was zoomed and it was now 300 wide. The 0.1 would now translate to 0.1 * 300 = 30. You can store the "percentage" X,Y pairs in PointF() instead of Point().

Here's a quick example to play with:

public partial class Form1 : Form
{

    private List<Tuple<PointF, PointF>> Points = new List<Tuple<PointF, PointF>>();

    public Form1()
    {
        InitializeComponent();
        this.Shown += new EventHandler(Form1_Shown);

        this.pictureBox1.BackColor = Color.Red;
        this.pictureBox1.SizeChanged += new EventHandler(pictureBox1_SizeChanged);
        this.pictureBox1.Paint += new PaintEventHandler(pictureBox1_Paint);
    }

    void Form1_Shown(object sender, EventArgs e)
    {
        // convert absolute points:
        Point ptStart = new Point(100, 25);
        Point ptEnd = new Point(300, 75);

        // to percentages:
        PointF ptFstart = new PointF((float)ptStart.X / (float)pictureBox1.Width, (float)ptStart.Y / (float)pictureBox1.Height);
        PointF ptFend = new PointF((float)ptEnd.X / (float)pictureBox1.Width, (float)ptEnd.Y / (float)pictureBox1.Height);

        // add the percentage point to our list:
        Points.Add(new Tuple<PointF, PointF>(ptFstart, ptFend));
        pictureBox1.Refresh();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        // increase the size of the picturebox 
        // watch how the line(s) change with the changed picturebox
        pictureBox1.Size = new Size(pictureBox1.Width + 50, pictureBox1.Height + 50);
    }

    void pictureBox1_SizeChanged(object sender, EventArgs e)
    {
        pictureBox1.Refresh();
    }

    void pictureBox1_Paint(object sender, PaintEventArgs e)
    {
        foreach (Tuple<PointF, PointF> tup in Points)
        {
            // convert the percentages back to absolute coord based on the current size:
            Point ptStart = new Point((int)(tup.Item1.X * pictureBox1.Width), (int)(tup.Item1.Y * pictureBox1.Height));
            Point ptEnd = new Point((int)(tup.Item2.X * pictureBox1.Width), (int)(tup.Item2.Y * pictureBox1.Height));
            e.Graphics.DrawLine(Pens.Black, ptStart, ptEnd);
        }
    }

}

Upvotes: 1

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