How do I choose a pixel format when creating a new Texture2D?

Question

I'm using the SharpDX Toolkit, and I'm trying to create a Texture2D programmatically, so I can manually specify all the pixel values. And I'm not sure what pixel format to create it with.

SharpDX doesn't even document the toolkit's PixelFormat type (they have documentation for another PixelFormat class but it's for WIC, not the toolkit). I did find the DirectX enum it wraps, DXGI_FORMAT, but its documentation doesn't give any useful guidance on how I would choose a format.

I'm used to plain old 32-bit bitmap formats with 8 bits per color channel plus 8-bit alpha, which is plenty good enough for me. So I'm guessing the simplest choices will be R8G8B8A8 or B8G8R8A8. Does it matter which I choose? Will they both be fully supported on all hardware?

And even once I've chosen one of those, I then need to further specify whether it's SInt, SNorm, Typeless, UInt, UNorm, or UNormSRgb. I don't need the sRGB colorspace. I don't understand what Typeless is supposed to be for. UInt seems like the simplest -- just a plain old unsigned byte -- but it turns out it doesn't work; I don't get an error, but my texture won't draw anything to the screen. UNorm works, but there's nothing in the documentation that explains why UInt doesn't. So now I'm paranoid that UNorm might not work on some other video card.

Here's the code I've got, if anyone wants to see it. Download the SharpDX full package, open the SharpDXToolkitSamples project, go to the SpriteBatchAndFont.WinRTXaml project, open the SpriteBatchAndFontGame class, and add code where indicated:

// Add new field to the class:
private Texture2D _newTexture;

// Add at the end of the LoadContent method:
_newTexture = Texture2D.New(GraphicsDevice, 8, 8, PixelFormat.R8G8B8A8.UNorm);
var colorData = new Color[_newTexture.Width*_newTexture.Height];
_newTexture.GetData(colorData);
for (var i = 0; i < colorData.Length; ++i)
    colorData[i] = (i%3 == 0) ? Color.Red : Color.Transparent;
_newTexture.SetData(colorData);

// Add inside the Draw method, just before the call to spriteBatch.End():
spriteBatch.Draw(_newTexture, new Vector2(0, 0), Color.White);

This draws a small rectangle with diagonal lines in the top left of the screen. It works on the laptop I'm testing it on, but I have no idea how to know whether that means it's going to work everywhere, nor do I have any idea whether it's going to be the most performant.

What pixel format should I use to make sure my app will work on all hardware, and to get the best performance?

Part of the question - uint will return values as an integer in your shader, unorm returns them as floating point numbers in the range 0.0..1.0 which is what is generally expected in a shader for colors, and what you generally need to return from the pixel shader. If you sampled the "int" texture and transformed the values in your shader it would probably work. — jcoder
@J99: To my knowledge, there's no shader in the picture. I'm just trying to use SpriteBatch to put a bitmap on the screen, and as far as I can tell, DirectX calls bitmaps "textures". Are there relevant details that I'm missing? — Joe White
Ok there will be a shader used internally in the library I exepct but if you don't have access to it then this won't work. Sorry — jcoder

Jens Nolte Jens Nolte · Accepted Answer · 2012-11-25T07:21:09

The formats in the SharpDX Toolkit map to the underlying DirectX/DXGI formats, so you can, as usual with Microsoft products, get your info from the MSDN:

DXGI_FORMAT enumeration (Windows)

32-bit-textures are a common choice for most texture scenarios and have a good performance on older hardware. UNorm means, as already answered in the comments, "in the range of 0.0 .. 1.0" and is, again, a common way to access color data in textures.

If you look at the Hardware Support for Direct3D 10Level9 Formats (Windows) page you will see, that DXGI_FORMAT_R8G8B8A8_UNORM as well as DXGI_FORMAT_B8G8R8A8_UNORM are supported on DirectX 9 hardware. You will not run into compatibility-problems with both of them.

Performance is up to how your Device is initialized (RGBA/BGRA?) and what hardware (=supported DX feature level) and OS you are running your software on. You will have to run your own tests to find it out (though in case of these common and similar formats the difference should be a single digit percentage at most).

How do I choose a pixel format when creating a new Texture2D?

1 Answers