45 lines
1.3 KiB
C
45 lines
1.3 KiB
C
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#include <c3d/maths.h>
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void Mtx_PerspTilt(C3D_Mtx* mtx, float fovx, float invaspect, float near, float far)
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{
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// Notes:
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// We are passed "fovy" and the "aspect ratio". However, the 3DS screens are sideways,
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// and so are these parameters -- in fact, they are actually the fovx and the inverse
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// of the aspect ratio. Therefore the formula for the perspective projection matrix
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// had to be modified to be expressed in these terms instead.
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// Notes:
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// fovx = 2 atan(tan(fovy/2)*w/h)
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// fovy = 2 atan(tan(fovx/2)*h/w)
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// invaspect = h/w
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// a0,0 = h / (w*tan(fovy/2)) =
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// = h / (w*tan(2 atan(tan(fovx/2)*h/w) / 2)) =
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// = h / (w*tan( atan(tan(fovx/2)*h/w) )) =
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// = h / (w * tan(fovx/2)*h/w) =
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// = 1 / tan(fovx/2)
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// a1,1 = 1 / tan(fovy/2) = (...) = w / (h*tan(fovx/2))
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float fovx_tan = tanf(fovx/2);
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C3D_Mtx mp;
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Mtx_Zeros(&mp);
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// Build standard perspective projection matrix
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mp.r[0].x = 1.0f / fovx_tan;
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mp.r[1].y = 1.0f / (fovx_tan*invaspect);
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mp.r[2].z = (near + far) / (near - far);
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mp.r[2].w = (2 * near * far) / (near - far);
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mp.r[3].z = -1.0f;
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// Fix depth range to [-1, 0]
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C3D_Mtx mp2;
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Mtx_Identity(&mp2);
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mp2.r[2].z = 0.5;
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mp2.r[2].w = -0.5;
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Mtx_Multiply(mtx, &mp2, &mp);
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// Rotate the matrix one quarter of a turn CCW in order to fix the 3DS screens' orientation
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Mtx_RotateZ(mtx, M_TAU/4, true);
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}
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