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POConfused Regarding World View Projection Matrix question for Ray Tracing using XNA
 

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  1. POConfused Regarding World View Projection Matrix question for Ray Tracing using XNA
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    <p>So I've decided to rewrite an old ray tracer I had which was written in C++ and to do it in C#, leveraging the XNA framework.</p> <p>I still have my old book and can follow the notes however I am confused regarding a few ideas and I was wondering whether someone could articulate it nicely.</p> <pre> <code> for each x pixel do for each y pixel do //Generate Ray //1 - Calculate world coordinates of current pixel //1.1 Calculate Normalized Device coordinates for current pixel 1- to -1 (u, v) u = (2*x/ WIDTH) - 1 ; v = (2*y/HEIGHT) - 1 ; Vector3 rayDirection = -1*focalLength + u'*u + v'*v </code> </pre> <p>In the above code u' and v' are the orthnormal basis calculated for the given camera (I know the same names make it confusing)</p> <p>If I follow the book and do it the way it expresses, it works. However I am trying to leverage XNA and getting confused on how to perform the same actions but using Matrices.</p> <p>So I've tried to replace the following steps with the XNA code</p> <pre> <code> class Camera { public Camera(float width, float height) { AspectRatio = width/height; FOV = Math.PI / 2.0f; NearPlane = 1.0f; FarPlane = 100.0f; ViewMatrix = Matrix.CreateLookAt(Position, Direction,this.Up); ProjectionMatrix=Matrix.CreatePerspectiveFieldOfView(FOV, AspectRatio,NearPlane,FarPlane); } } </code> </pre> <p>It's at this point I'm confused in the order of operations I am supposed to apply in order to get the direction vector for any pixel (x, y) ?</p> <p>In my head I'm thinking: (u,v) = ProjectionMatrix * ViewMatrix * ModelToWorld * Vertex(in model space)</p> <p>Therefore it would make sense that</p> <p>Vertex (in world space) = Inverse(ViewMatrix) * Inverse(ProjectionMatrix) * [u, v, 0]</p> <p>I also remembered something about how the view Matrix can be Transposed as well as Inverted since it is orthonormal.</p>
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