Quad Texture to Pixel Screen Space (DirectX 11)

Question

I think I must be using the wrong wording for what I want, because I seached and just kept finding pixel shader questions. But this seems like something that anyone making a 2D game would want.

Basically I have my quad, my loaded texture in a ID3D11ShaderResourceView and I can draw it to the screen using coordinates of -1.0 to 1.0.

But what I want to accomplish is drawing based on pixels.

i.e.

I would want to draw a 20x20 pixel image to coordinates 100,100 on a 800x600 screen. But, I want to do this by manipulating the quad to the correct size and position to mimic this (which is, I assume, a common way to do 2D in DirectX11).

As I said, I am able to draw a texture to screen space at the moment but I am lost as to what calculations or methods would be required to convert this to pixel-based drawing.

Thank you :)

Answer 1

The normal way to do this would be to create a matrix representing the transformation from game world coordinates to screen coordinates. Note that I never mention resolution here because it does not come in to play directly. For such a projection the only thing important is the aspect ration.

In your vertex shader you would just multiply the input position with the matrix and output the new position to your pixel shader. Alternatively if you are not using shaders (or well, if they are hidden from you) you could apply the matrix manually to each vertex before you send it to the graphics device.

How to create such a matrix requires just a few calculations on paper. For example: if your game world coordinates are from 0~100 and your screen coordinates are -1~1 you would need to scale by 0.02 and translate by -1.0 (in that order). Remember that you can combine multiple successive matrix operations by pre-multiplying the matrices.