source of Intersect (EX9.Geometry Quad)

gistfile1.pas

for index := FromSlice to ToSlice do
  begin

    //get transform matrices
    QuadTransform := FQuadTransformManager.ModelMatrix[index];
    LineTransform := FLineTransformManager.ModelMatrix[index];

    //set quad and line (quad from (-0.5, -0.5, 0) to (0.5, 0.5, 0), line on z-axis )
    PQuad := TD3DXVector3.Create(0, 0, 0);
    nQuad := TD3DXVector3.Create(0, 0, 1);
    PLine1 := TD3DXVector3.Create(0, 0, -0.5);
    PLine2 := TD3DXVector3.Create(0, 0, 0.5);

    //transform line
    D3DXVec3TransformCoord(PLine1, PLine1, LineTransform);
    D3DXVec3TransformCoord(PLine2, PLine2, LineTransform);

    //transform line into object space of the quad
    InvQuadTransform := TD3DXMatrix.Create( 0, 0, 0, 0,
                                    0, 0, 0, 0,
                                    0, 0, 0, 0,
                                    0, 0, 0, 1);
                                    
    D3DXMatrixInverse(InvQuadTransform, nil, QuadTransform);
    D3DXVec3TransformCoord(PLine1, PLine1, InvQuadTransform);
    D3DXVec3TransformCoord(PLine2, PLine2, InvQuadTransform);

    //get line direction vector
    D3DXVec3Subtract(rLine, PLine2, Pline1);

    //check attitude of line and plane
    denom := nQuad.x*rLine.x + nQuad.y*rLine.y + nQuad.z*rLine.z;

    //if NOT parallel do calculations
    if denom <> 0 then
    begin

      FIntersectsPlanePin.Value[index] := 1;

      //get intersection position on line
      LineAlpha := (nQuad.x*(PQuad.x - PLine1.x) + nQuad.y*(PQuad.y - PLine1.y) +
                    nQuad.z*(PQuad.z - PLine1.z) ) / denom;

      //calculate intersection point
      IntPoint := TD3DXVector3.Create( PLine1.x + LineAlpha*rLine.x, PLine1.y + LineAlpha*rLine.y,
                               PLine1.z + LineAlpha*rLine.z);

      FLineAlphaPin.Value[index] := LineAlpha - 0.5;

      FQuadAlphaPin.Value[index] := IntPoint.x;
      FQuadBetaPin.Value[index]  := IntPoint.y;

      //check if intersection is on quad
      FIntersectsQuadPin.AsBool[index] := (IntPoint.x <= 0.5) and (IntPoint.x >= -0.5) and
                                          (IntPoint.y <= 0.5) and (IntPoint.y >= -0.5);

       //check if intersection is on line segment
      FIntersectsLineSegmentPin.AsBool[index] := FIntersectsQuadPin.AsBool[index] and (LineAlpha <= 1) and (LineAlpha >= 0);

      //transform intersection point into world space
      D3DXVec3TransformCoord(IntPoint, IntPoint, QuadTransform);
      FIntersectionPoint.setV3(index, IntPoint)

    end

    //nothing to do if parallel
    else
    begin

      FIntersectsPlanePin.Value[index] := 0;
      FIntersectsLineSegmentPin.Value[index] := 0;
      FIntersectsQuadPin.Value[index] := 0;
      FLineAlphaPin.Value[index] := 0;
      FQuadAlphaPin.Value[index] := 0;
      FQuadBetaPin.Value[index]  := 0;

    end;
    
  end;