flip coordinates when drawing to control

Question

I am drawing a graph on a control, but 0,0 is at the top-left hand corner of the control. Is there a way to flip the coordinates so that 0,0 is at the lower left corner of the control?

Answer 1

No, but using the Size (or Height) properties of the control, it is easy to calculate flipped coordinates: Just draw to Height-y.

Answer 2

Not that I know of but if you use (x,Control.Height-y) you get the same effect.

Answer 3

in short no, however if i am drawing on controls a lot i have a few functions that help me:

Point GraphFromRaster(Point point)  {...}
Point RasterFromGraph(Point point)  {...}

this way i keep all the conversion in one place, no worrying about things like y - this.Height scattered about the code.

Answer 4

If you are using WinForms, then you might find that you can flip the Y-Axis using Graphics.ScaleTransform:

private void ScaleTransformFloat(PaintEventArgs e)
{
    // Begin graphics container
    GraphicsContainer containerState = e.Graphics.BeginContainer();

    // Flip the Y-Axis
    e.Graphics.ScaleTransform(1.0F, -1.0F);

    // Translate the drawing area accordingly
    e.Graphics.TranslateTransform(0.0F, -(float)Height);

    // Whatever you draw now (using this graphics context) will appear as
    // though (0,0) were at the bottom left corner
    e.Graphics.DrawRectangle(new Pen(Color.Blue, 3), 50, 0, 100, 40);

    // End graphics container
    e.Graphics.EndContainer(containerState);

    // Other drawing actions here...
}

Note that I haven't tested this, but the documentation doesn't suggest passing a negative scaling factor is invalid.

You only need to include the begin/end container calls if you want to do additional drawing using the regular coordinate system as well. More information on graphics containers is available on MSDN.

Answer 5

Here's a simple UserControl that demonstrates how to do this:

public partial class UserControl1 : UserControl
{
    public UserControl1()
    {
        SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.UserPaint | ControlStyles.DoubleBuffer, true);

        InitializeComponent();
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        e.Graphics.ScaleTransform(1.0F, -1.0F);
        e.Graphics.TranslateTransform(0.0F, -(float)Height);
        e.Graphics.DrawLine(Pens.Black, new Point(0, 0), new Point(Width, Height));

        base.OnPaint(e);
    }
}