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# Yet another frustum question

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### #1resle  Members

Posted 04 December 2008 - 10:28 PM

Hi, I've correctly implemented a frustum class, so at least the question is not about "how to build a frustum" as usual ;) When I create a frustum plane, I end it with a D3DXPlaneNormalize call. I don't know how to express myself exactly but.. isn't the "translation" component of the View matrix lost in this process? I am asking this because then I check some vertices against the frustum, and said vertices' coordinates are relative to the whole "world". So for example: - I've got this far far vertex at Vec3(3000,2500,7000). - I translate the view matrix to (3000,2500,6950) - The vertex is now viewable at a certain distance in the middle of the screen - I build the frustum - Check the frustum against Vec3(3000,2500,7000) : fail Should I somehow... uhm... "normalize" the vertex as well perhaps?

### #2resle  Members

Posted 09 December 2008 - 11:48 PM

Frustum building:

// AS SEEN A BILLION TIMES ON A MILLION TUTORIALS...function tfrustum.Build(mat_view, mat_proj:d3dxmatrix;begin    D3DXMatrixInverse(mat_comb, nil, mat_view);    D3DXMatrixMultiply(mat_comb, matrix_proj, mat_comb);    // Left clipping plane    planes[0].a := matComb._14 + matComb._11;    planes[0].b := matComb._24 + matComb._21;    planes[0].c := matComb._34 + matComb._31;    planes[0].d := matComb._44 + matComb._41;    D3DXPlaneNormalize(planes[0],planes[0]);    // Right clipping plane    planes[1].a := matComb._14 - matComb._11;    planes[1].b := matComb._24 - matComb._21;    planes[1].c := matComb._34 - matComb._31;    planes[1].d := matComb._44 - matComb._41;    D3DXPlaneNormalize(planes[1],planes[1]);    // Top clipping plane    planes[2].a := matComb._14 - matComb._12;    planes[2].b := matComb._24 - matComb._22;    planes[2].c := matComb._34 - matComb._32;    planes[2].d := matComb._44 - matComb._42;    D3DXPlaneNormalize(planes[2],planes[2]);    // Bottom clipping plane    planes[3].a := matComb._14 + matComb._12;    planes[3].b := matComb._24 + matComb._22;    planes[3].c := matComb._34 + matComb._32;    planes[3].d := matComb._44 + matComb._42;    D3DXPlaneNormalize(planes[3],planes[3]);    // Near clipping plane    planes[4].a := matComb._13;    planes[4].b := matComb._23;    planes[4].c := matComb._33;    planes[4].d := matComb._43;    D3DXPlaneNormalize(planes[4],planes[4]);    // Far clipping plane    planes[5].a := matComb._14 - matComb._13;    planes[5].b := matComb._24 - matComb._23;    planes[5].c := matComb._34 - matComb._33;    planes[5].d := matComb._44 - matComb._43;    D3DXPlaneNormalize(planes[5],planes[5]);

Frustum checking (sphere):

function tfrustum.RadiusInside(pos:d3dxvector; radius:float)begin    result:=(D3DXPlaneDotCoord(planes[4], pos)>-radius)            and            (D3DXPlaneDotCoord(planes[3], pos)>-radius)            and            (D3DXPlaneDotCoord(planes[2], pos)>-radius)            and            (D3DXPlaneDotCoord(planes[1], pos)>-radius)            and            (D3DXPlaneDotCoord(planes[0], pos)>-radius)            and            (D3DXPlaneDotCoord(planes[5], pos)>-radius)            ;end;

Practical example:

// SETTING UP THE VIEW MATRIX TO POSITION 1000,0,1000, ROTATION 0,0,0D3DXMatrixTranslation(matrix_pos,1000,0,1000);D3DXQuaternionRotationYawPitchRoll(quaternion_rot,0,0,0);D3Dxmatrixrotationquaternion(matrix_rot,quaternion_rot);D3DXMatrixMultiply(matrix_view,matrix_rot,matrix_pos);// BUILDING THE FRUSTUM (matrix_proj never changes)frustum.Build(matrix_view, matrix_proj);// CHECKINGif frustum.RadiusInside(d3dxvec3(1010,0,1010), 100) then  MessageBox('Pleasure') else MessageBox('Migraine');

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