"Wrap-around" effect with a Direct3D.Texture

Question

Given a destination rectangle and an x/y offset value, I need an image to be drawn within the confines of that destination rectangle. If the offset would push the image off the edge of the rectangle, then the part that "pushes out" should appear on the opposite side of the destination rectangle. In simplest terms, I need a scrolling background.

In GDI, I can accomplish this with an "ImageAttributes" object that uses a tile wrap mode:

ImageAttributes attributes = new ImageAttributes();
attributes.SetWrapMode(System.Drawing.Drawing2D.WrapMode.Tile);

Rectangle rectangle = new Rectangle(0, 0, (int)width, (int)height);
g.DrawImage(bmp, rectangle, -x, -y, width, height, GraphicsUnit.Pixel, attributes);

Now, I need a way to do this in DirectX. Assume that this is the method I have right now:

public void RenderTexture(PrismDXObject obj, D3D.Texture texture, int xOffset, int yOffset)
{
    if (obj != null && texture != null)
    {
        _renderSprite.Begin(D3D.SpriteFlags.AlphaBlend);
        _renderSprite.Draw(texture,
            new Rectangle(0, 0, (int)obj.Width, (int)obj.Height),
            new Vector3(0.0f, 0.0f, 0.0f),
            new Vector3((int)obj.Left, (int)obj.Top, 0.0f),
            obj.RenderColor);
            _renderSprite.End();
        }
    }
}

...where "_renderSprite" is a D3D.Sprite, and PrismDXObject is a simple class that stores x/y/width/height/color. How can I update this method so that xOffset and yOffset can be used to make the texture wrap? Remember, my end-goal is a scrolling background that loops as the player walks forward.

Incidentally, that RenderTexture() method is meant to be a "library method" which can be called from anywhere in my program... so if I'm doing something really inefficient or ill-advised, I'd welcome a friendly warning! My main concern is getting the wrapping background to work, though.

Answer 1

I'm not sure that the sprite mechanism allows for what I'm about to explain, but 2 triangles certainly do. If this does not work with sprites, use triangles directly:

What you're asking for is directly supported by the texturing subsystem, it is called texture wrapping.

• When you specify the texture coordinates that your quad will use, instead of using the 0,0-1,1 range, you can use 0+xoffset/tex_x_size, 0+yoffset/tex_y_size, 1+xoffset/tex_x_size, 1+yoffset/tex_y_size for your texture coordinates.
• Then, the only thing left to do is to specify that the texture sampler you will use to map your background does texture wrapping. To do this, you need to set to D3DTADDRESS_WRAP the D3DSAMP_ADDRESSU and D3DSAMP_ADDRESSV sampler states. Note, this is the default for the sampler state.

that's it. Now, getting back to D3D.Sprite specifically, the Draw method takes a rectangle that tells which part of the texture to use. have you tried drawing xoffset, yoffset, xOffset+obj,Width, yoffset+obj.height ? This will only work if the sprite subsystem uses a sampler that has wrapping on, and I don't know how sprite is implemented internally.