How do I render an entire frame to a Texture2D?

Question

I asked a question here: C# XNA Make rendered screen a texture2d

But, I ended up not getting the exact result I was looking for since I didn't ask the question right.

In a game I am writing, I render an extremely large city out of objects, this can cause lag when moving the camera to view things that are off screen. I need a way to render then ENTIRE city, even the stuff that is off screen, and make it into a Texture2D.

The answer I chose for the last one didn't work entirely right because it only gets what is on screen, not what is off.

Answer 1

You can still use this approach.

For 3D Just move the camera much further away so that the entire city is in the view volume. [or make the view volume wider/higher if using orthographic projection]

You will have to make the size of the render target much bigger to accommodate the required resolution, but you will not be able to make a texture more than 4,096 pixels in either dimension.

If 4,096 sized textures is not enough, than you could look at making a number of textures

[EDIT]

For 2D just render the scene on a render target much larger than the screen size e.g 4096 pixels across, making sure that you render things with the same scale (i.e. if a building is 10 pixels across on screen, it should be 10 pixels across on the render target). This way you will get a much larger area of your city drawn. You can then draw subsections of this texture on the screen.

int vpw = graphics.GraphicsDevice.Viewport.Width;
int vph = graphics.GraphicsDevice.Viewport.Height;

spriteBatch.Begin();

//camera.Position is the point in  the world you want at the centre of the screen
//cityRect is the sub-area of the large background you want to display
Rectangle cityRect=new Rectangle(
                (int)(camera.Position.X-vpw/2), 
                (int)(camera.Position.Y-vph/2),
                vpw, 
                vph);

//cityTexture is the large pre-rendered texture
spriteBatch.Draw(cityTexture, Vector2.Zero, 
            cityRect, Color.White);
spriteBatch.End();