4-point transform images

Question

I need to transform bitmap images with their 4 corner points moved from one location to another.

Any code that can run on Windows, C#/VB.NET preferably, even help ho

Answer 1

Easier than simulating a perspective distort using image manipulation, you could use OpenGL or DirectX (XNA) to actually perform the perspective display.

Render a simple quad with your image as the texture map. Setup your scene, render to a buffer, and you have your image.

Update It turns out that XNA is a ridiculous library (geared toward making games and nothing else, yawn). Managed DirectX requires a brain lobotomy. OpenGL is easy to use, but lacks image loading code. That leaves us with WPF:

alt text http://praeclarum.org/so/persp.png

The image could be improved by forcing WPF into anti-alias mode (why oh why Microsoft are you so short-sighted?), and by not using Aero glass which forces that 1 pixel black border on all screenshots (or by removing that 1 pixel border).

(Sorry for the length of this code, but WPF is a chatty API.)

public partial class Window1 : Window {
    const float ANGLE = 30;
    const float WIDTH = 8;
    public Window1() {
        InitializeComponent();

        var group = new Model3DGroup();
        group.Children.Add(Create3DImage(@"C:\Users\fak\Pictures\so2.png"));
        group.Children.Add(new AmbientLight(Colors.White));

        ModelVisual3D visual = new ModelVisual3D();
        visual.Content = group;
        viewport.Children.Add(visual);
    }

    private GeometryModel3D Create3DImage(string imgFilename) {
        var image = LoadImage(imgFilename);

        var mesh = new MeshGeometry3D();
        var height = (WIDTH * image.PixelHeight) / image.PixelWidth;
        var w2 = WIDTH / 2.0;
        var h2 = height / 2.0;
        mesh.Positions.Add(new Point3D(-w2, -h2, 0));
        mesh.Positions.Add(new Point3D(w2, -h2, 0));
        mesh.Positions.Add(new Point3D(w2, h2, 0));
        mesh.Positions.Add(new Point3D(-w2, h2, 0));
        mesh.TriangleIndices.Add(0);
        mesh.TriangleIndices.Add(1);
        mesh.TriangleIndices.Add(2);
        mesh.TriangleIndices.Add(0);
        mesh.TriangleIndices.Add(2);
        mesh.TriangleIndices.Add(3);
        mesh.TextureCoordinates.Add(new Point(0, 1)); // 0, 0
        mesh.TextureCoordinates.Add(new Point(1, 1));
        mesh.TextureCoordinates.Add(new Point(1, 0));
        mesh.TextureCoordinates.Add(new Point(0, 0));

        var mat = new DiffuseMaterial(new ImageBrush(image));
        mat.AmbientColor = Colors.White;

        var geometry = new GeometryModel3D();
        geometry.Geometry = mesh;
        geometry.Material = mat;
        geometry.BackMaterial = mat;

        geometry.Transform = new RotateTransform3D(
            new AxisAngleRotation3D(new Vector3D(0,1,0), ANGLE),
            new Point3D(0, 0, 0));

        return geometry;
    }

    public static BitmapSource LoadImage(string filename) {
        return BitmapDecoder.Create(new Uri(filename, UriKind.RelativeOrAbsolute),
            BitmapCreateOptions.None, BitmapCacheOption.Default).Frames[0];
    }
}

And the required XAML: