Render Targets in XNA
WARNING: technical post ahead! I had never investigated render targets in XNA before because I didn't understand how/when they would be useful. now that I understand them, I want to use them all over the place! I thought I'd give a brief explanation here on what I've discovered in the last few days in case anyone finds it interesting. I'll probably follow this up with another post in a few days to show an example of where I'm using it right now. XNA's RenderTarget2D class is an extension of the Texture2D class. while I won't claim to know the specifics about how it works, the net result is that you can draw sprites to a RenderTarget2D rather than directly to the video buffer. this creates a texture to which you can apply any kind of processing. you can composite them together, or turn around and draw this texture directly to the video buffer, or apply a filter to make everything more brown to make everything look more like modern games. MW's HUD is a great candidate to use a render target, so it makes a good example of when/how to use them. right now, each item on the HUD knows its "local" coordinates within the HUD, but those must be translated to "screen" coordinates before it can be drawn. I also need to be careful with z-ordering (layering) to ensure that the elements of the HUD area always drawn on top of the gameplay. this has always felt wrong to me, but I couldn't think of a better solution until now. however, if I simply draw all of the components of the HUD to a render target, they don't need to know where on the screen the HUD is being drawn, nor do I need to worry as much about z-ordering. they only need to know where they are on the HUD (relative to its upper left corner) and what z-ordering to have within it. here's how it would work... 1) stop drawing the HUD components directly to the flight screen:
1) create the components of the HUD:
2) create a RenderTarget2D that has the same dimensions as the HUD overlay:
3) draw each component to the render target with coordinates relative to upper left corner of the target and with the appropriate z-ordering (e.g., the box that shows your crystal should be drawn behind the crystal itself). the result is a single "painting" which can be used just like any other texture/sprite:
4) draw the entire HUD texture to the bottom of the screen:
(I haven't actually converted the HUD to use a render target yet, so this is just a mockup of how it would work, but it's on the agenda) one cool thing to note is that this would make it easy to display the HUD on the top of the screen if the player would prefer that. to accomplish that, I could have the gameplay field render itself to a separate render target, creating two final textures which can just be rearranged. P.S.: the screenshot key (F5) utilizes render targets to capture everything that is occurring on screen in one texture. then, because RenderTarget2D is an extension of Texture2D, I can just call SaveAsPng() to save the screenshot to disk!