Here is my attempt at using XNA to duplicate some of the UI functionality on WP7. Well, not really duplicate so much as “create a passing resemblance to”. The menu is pretty boring. I’ve been trying to come up with a good idea to make it interesting, and think I finally have something that will be worth the effort. That’ll probably be the next movie. The first WP7 phones are supposed to be released in the U.S. on November 8th…
In a previous post about texture modification, I mentioned the evils of transferring data from the GPU to the CPU, and then presented an example showing one way to avoid doing it. The post wasn’t really about deformable 2D terrain or collision detection, but was intended to help newer game programmers open up a new way of thinking when it comes to using the GPU to accomplish tasks.
Since that post, and the one showing a video of my WP7 game, I’ve received a couple of questions about how I do the collision detection in Guardian, which would seem to require the use of Texture2D.GetData.
I’ve had a couple of questions about what changes are needed to get the texture modification tutorial to work in XNA 3.1. So, here’s a 3.1 version of the project, and a quick overview of the major things that need to change. You need to create the depth/stencil buffer yourself, set it on the GraphicsDevice when setting the render target, and restore the previous buffer when you’re done. RenderTarget2D can’t be used directly as a texture, you must call RenderTarget2D.GetTexture…
Sometimes you need to modify a texture while your game is running, and there are a number of ways to do this. One of the first things newer game programmers often try to do is use Texture2D.GetData to copy the texture data from the GPU to an array on the CPU, modify the bytes, and then send it back to the GPU with Texture2D.SetData.
This is a bad idea on many, levels. Beyond issues with pipeline stalls, GetData and SetData can be slow, especially when working with a large texture. Any time you’re tempted grab data from the GPU for use on the CPU you should very carefully consider all of your options. There are often other solutions that let you keep the data entirely on the GPU and accomplish the same thing.
This tutorial will use an example that could be solved with GetData and SetData, and show you another alternative using render targets and the stencil buffer that will let you perform the same function entirely on the GPU.
Procedural Planet video showing the space-to-surface transition, as well as the tank driving around a bit. I’m pretty happy with how it looks, but there are a lot of things that still need to be fixed.
I needed a bit of a diversion from the planet rendering itself, into something that would give some purpose behind it. Why is the planet there? Well, what better use is there for a planet than driving a tank on it?
We left off in part 1 talking about the initial failures with my GPU geometry map shader. I did fail to mention that there was a bright spot the first time I ran the new code – it was amazingly fast. So fast I was able to increase the noise octaves from the 5 that would run reasonably well on the CPU up to 30 and still run at well over 60fps. I have to admit that I spent some of that first 18 hour day just roaming around on a barren, reddish planet. That huge improvement in performance made the pain to come well worth it.
So, at the end of part 1 we set up the C# code for executing the geometry map shader. Now let’s take a look at the shader itself.
Going to write up something useful tomorrow, but for now here are a few screenshots…
Previously I mentioned I was going to do a mulligan on my procedural planet engine. The few hours I’ve worked on it so far have lead to a beautiful new architecture that’s doing most of the same things as before, as well as some major new things, using about 25% of the code.
When developing the iPhone version of Guardian I manually created my sprite sheets. I used individual sprites up until the end so everything was pretty much set in stone by the time I created the the sprite sheet. Even then I ended up having to recreate the sprite sheet two or three times, and let me tell you, manually figuring out the texture coordinates isn’t a particularly pleasant experience. In this case I believe I made the right choice. There were few enough sprites that I would have spent more time creating the tool than I would have saved.