XNA 4.0 InvalidOperationException was unhandeled

Question

I am using this tutorial to learn a little XNA, and i keep running into problems. I've had to convert alot of the code, since it seems the tutorial do not use XNA 4.0.

But lets cut to the chase!

float aXPosition = (float)(-mCarWidth / 2 + mCarPosition.X + aMove * Math.Cos(mCarRotation));
            float aYPosition = (float)(-mCarHeight / 2 + mCarPosition.Y + aMove * Math.Sin(mCarRotation));
            Texture2D aCollisionCheck = CreateCollisionTexture(aXPosition, aYPosition);

            //Bruke GetData til å fylle en array med fargen på pixlene ved collisons texturen
            int aPixels = mCarWidth * mCarHeight;
            Color[] myColors = new Color[aPixels];
            aCollisionCheck.GetData<Color>(0, new Rectangle((int)(aCollisionCheck.Width / 2 - mCarWidth / 2),
                (int)(aCollisionCheck.Height / 2 - mCarHeight / 2), mCarWidth, mCarHeight), myColors, 0, aPixels);

The error i get when i try to debug the code says: InvalidOperationException was unhandeled, The render Target must not be set on the device when it is used as a texture.

I have no clue what to do.

Answer 1

This basically means exactly what it says.

You have to unset the render target from the device by calling GraphicsDevice.SetRenderTarget(null) (or setting it to a different render target). Because you can't use it as both a source texture and a destination buffer at the same time.

Keep in mind that, in this version of XNA, there is no ResolveRenderTarget. Render targets simply are textures.

---

Note that the tutorial that you are using is pretty terrible. Reading back from a render target like this is extremely slow. Especially seeing as the operations that it is using the render target for (selecting pixels in a transformed region) could easily be done efficiently on the CPU. Consider using this better, official example.