Question

I’m attempting to draw many textures onto one texture to create a map for an RTS game, and while I can can draw an individual texture onscreen, drawing them all to a render target seems to have no effect (the window remains AliceBlue when debugging) . I am trying to determine whether or not anything is even drawn to the render target, and so I am trying to save it as a Jpeg to a file and then view that Jpeg, from my desktop. How can I access that Jpeg from MemoryStream?

protected override void LoadContent()
{

         spriteBatch = new SpriteBatch(GraphicsDevice);
         gridImage = new RenderTarget2D(GraphicsDevice, 1000, 1000);
         GraphicsDevice.SetRenderTarget(gridImage);
         GraphicsDevice.Clear(Color.AliceBlue);
         spriteBatch.Begin();


         foreach (tile t in grid.tiles)
         {
             Texture2D dirt = Content.Load<Texture2D>(t.texture);
             spriteBatch.Draw(dirt, t.getVector2(), Color.White);
         }
         test = Content.Load<Texture2D>("dirt");


             GraphicsDevice.SetRenderTarget(null);
             MemoryStream memoryStream = new MemoryStream();

            gridImage.SaveAsJpeg(memoryStream, gridImage.Width, gridImage.Height); //Or SaveAsPng( memoryStream, texture.Width, texture.Height )



         //    rt.Dispose();
             spriteBatch.End();
    }

Answer 1

I made a simple screenshot method,

  void Screenie()
            {
                int width = GraphicsDevice.PresentationParameters.BackBufferWidth;
                int height = GraphicsDevice.PresentationParameters.BackBufferHeight;

                //Force a frame to be drawn (otherwise back buffer is empty) 
                Draw(new GameTime());

                //Pull the picture from the buffer 
                int[] backBuffer = new int[width * height];
                GraphicsDevice.GetBackBufferData(backBuffer);

                //Copy to texture
                Texture2D texture = new Texture2D(GraphicsDevice, width, height, false, GraphicsDevice.PresentationParameters.BackBufferFormat);
                texture.SetData(backBuffer);
                //Get a date for file name
                DateTime date = DateTime.Now; //Get the date for the file name
                Stream stream = File.Create(SCREENSHOT FOLDER + date.ToString("MM-dd-yy H;mm;ss") + ".png"); 

                //Save as PNG
                texture.SaveAsPng(stream, width, height);
                stream.Dispose();
                texture.Dispose();
            }

Also, Are you loading Texture2D dirt = Content.Load<Texture2D>(t.texture); Every frame? It looks like it… Dont do that! That will cause massive lag loading hundreds of tiles, hundreds of times per second! instead make a global texture Texture2D DirtDexture and in your LoadContent() method do DirtTexture = Content.Load<Texture2D>(t.texture); Now when you draw you can do spriteBatch.Draw(DirtTexture,...

Do the same with spriteBatch = new SpriteBatch(GraphicsDevice); and
gridImage = new RenderTarget2D(GraphicsDevice, 1000, 1000);

You dont need to make new RenderTarget and Spritebatch each frame! Just do it in the Initialize() Method!

Also see RenderTarget2D and XNA RenderTarget Sample For more information on using render targets

EDIT: I realize its all in LoadContent, I didnt see that because the formatting was messed up, remember to add your Foreach (Tile, etc) in your Draw Method