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PORay setup in CUDA using OpenGL-supplied matrices
 

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  1. PORay setup in CUDA using OpenGL-supplied matrices
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    <p>I'm working on a project where I port my CUDA code for usage as a module in a big application which maintains its own OpenGL state. My module basically is a volume renderer. I am now facing the problem that I have to setup the rays of the volume renderer to exactly mimic the OpenGL camera, so that my volume renderering fits with the rest of the rendered scene.</p> <p>At the point where my CUDA code is called there is a viewing matrix (no model-view matrix) and a projection matrix set. I already extracted the frustum parameters and the camera position in world space. </p> <pre><code>u *= -c_pp.right; v *= -c_pp.top; Ray eyeRay; eyeRay.o = make_float3(c_camPosition); //origin eyeRay.d = normalize(make_float3(u, v, -c_pp.near)); //direction </code></pre> <p><code>u</code> and <code>v</code> are normalized screen coordinates running from <code>-1</code> to <code>1</code>. <code>c_pp</code> describes the view frustum using <code>top</code>, <code>right</code> and <code>near</code>. I'm now looking for the appropriate matrix I have to multiply with so that <code>eyeRay.d</code> shows in the right direction. So far using the viewing matrix or its transposed or inverted version failed.</p> <p><strong>Update</strong>:</p> <p>Changed <code>u *= -c_pp.right</code> to <code>u *= c_pp.right</code> and everything works by multiplying <code>eyeRay.d</code> with the inverse viewing matrix.</p> <p>Complete fixed code:</p> <pre><code>u *= c_pp.right; v *= -c_pp.top; Ray eyeRay; eyeRay.o = make_float3(c_camPosition); //origin eyeRay.d = make_float3(u, v, -c_pp.near)); //direction eyeRay.d = mul(c_invViewMatrix, eyeRay.d); </code></pre> <p>with <code>c_inViewMatrix</code> being the inverse view matrix.</p>
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    1. COIf you just want the view direction of the camera in worldspace, it should be the -Z axis of the camera's transformation matrix (minus because OpenGL's view axis points out of the screen), providing the camera itself is only described in world space terms.
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    2. CO@cbamver85: Thanks to your comment I found the solution; c_pp.right has the wrong sign, changing the code to u *= c_pp.right and everything works by multiplying the eyeRay.d vector with the inverse view matrix. After comparing the viewing direction of my CUDA code with the one I calculated in CPU code I found that there was something amiss and it turned out that the X component had the wrong sign all the time.
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