How do I override the paint method of a Winforms control to make it paint to a texture?

Question

I am trying to integrate Winforms with a SharpDX project, in order to use Winforms (and eventually WPF via HostElement) in my 3D app.

I need to create or configure a Control or Form such that I can:

a. Render it to a texture (that I can display as a sprite*)
b. Filter its input to remove mouse/keyboard events when the control is not active.

I have tried subclassing Control and Form, to override the OnPaint and OnPaintBackground but these have no effect on the child controls - or for that matter the forms borders (and even if they did they are not sufficient on their own as I am still left with a white square where I presume the 'parent' has been drawn).

How can I stop a Control or Form painting to the screen and instead draw only to a bitmap? (Is there some way I can override Graphics before the tree is painted, for example?)

*It needs to be done this way (as opposed to letting the control render to the screen) as Winforms doesn't support true transparency, so I need to clip colour coded pixels in my pixel shader.

(To confirm, I don't mean a DirectX texture specifically - I am happy with (in fact would prefer) a simple System.Drawing Bitmap)

Answer 1

Here is one way to start going about it:

• Create a derived control class so that we can expose InvokePaint which is protected
• Call our custom method to get the Control's image
• Test form needs a picture box and an instance of Mybutton

using System;
using System.Drawing;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1() { InitializeComponent(); }

        private void Form1_Load(object sender, EventArgs e)
        {
            // create image to which we will draw
            var img = new Bitmap(100, 100);

            // get a Graphics object via which we will draw to the image
            var g = Graphics.FromImage(img);

            // create event args with the graphics object
            var pea = new PaintEventArgs(g, new Rectangle(new Point(0,0), new Size(100,100)));

            // call DoPaint method of our inherited object
            btnTarget.DoPaint(pea);

            // modify the image with algorithms of your choice...

            // display the result in a picture box for testing and proof
            pictureBox.BackgroundImage = img;
        }
    }

    public class MyButton : Button
    {
        // wrapping InvokePaint via a public method
        public void DoPaint(PaintEventArgs pea)
        {
            InvokePaint(this, pea);
        }
    }
}