question about matrix transformation

[Zeus]

Hi,

i have a question about the matrix in irrlicht ... for my needs i have to initialize a matrix like that

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  matTransform._11(AgentHeading.x); matTransform._12(AgentSide.x);
  matTransform._21(AgentHeading.y); matTransform._22(AgentSide.y);
  matTransform._31(Tx);           matTransform._32(Ty);

but i have no acces to the members of the matrix ...

does anyone knows a way to do taht ?

thanks for helping

[Acki]

I didn't try, but maybe something like this:

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matrix4 matTransform;
matTransform(1,1) = AgentHeading.x;

EDIT: I don't know if the indices of the matrix you used are starting with 0
if not then it also can be like this:

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matrix4 matTransform;
matTransform(0,0) = AgentHeading.x;

[hybrid]

You can also access the fields via operator[]. Both functions start with 0 index.

[Zeus]

thanks for your answers ... ... i'll try it, but it will take a while till i can say you if it works ...

thanks again

zeus

[Acki]

I had a quick search and I found that your matrix probably is a DX matrix:

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// D3DMATRIX
typedef struct _D3DMATRIX {
    union {
        struct {
            float        _11, _12, _13, _14;
            float        _21, _22, _23, _24;
            float        _31, _32, _33, _34;
            float        _41, _42, _43, _44;

        };
        float m[4][4];
    };
} D3DMATRIX;

so it doesn't start with index 0, but with index 1 !!!
and because of this you'll have to decrement the indices !!!

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matrix4 matTransform;
matTransform(0,0) = AgentHeading.x; matTransform(0,1) = AgentSide.x
matTransform(1,0) = AgentHeading.y; matTransform(1,1) = AgentSide.y
matTransform(2,0) = Tx;             matTransform(2,1) = Ty;

if you want to use the [] operator the indices are like this:

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(0,0) => [0]
(0,1) => [1]
(0,2) => [2]
(0,3) => [3]
(1,0) => [4]
(1,1) => [5]
(1,2) => [6]
...
(3,3) => [15]

and then your code should look like this:

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matrix4 matTransform;
matTransform[0] = AgentHeading.x; matTransform[1] = AgentSide.x
matTransform[4] = AgentHeading.y; matTransform[5] = AgentSide.y
matTransform[8] = Tx;             matTransform[9] = Ty;

[Zeus]

hey ... thanks for your answer ... i couldn't test it so far couse an other problem occourred ...

i could determinate it to the function where the local space should be convert to global sapce ...

the function (with the 3x3 matrix out of my "tutorial") should look like this

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inline Vector2D PointToWorldSpace(const Vector2D &point,
                                    const Vector2D &AgentHeading,
                                    const Vector2D &AgentSide,
                                    const Vector2D &AgentPosition)
{
	//make a copy of the point
  Vector2D TransPoint = point;
  
  //create a transformation matrix
	C2DMatrix matTransform;

	//rotate
	matTransform.Rotate(AgentHeading, AgentSide);

	//and translate
	matTransform.Translate(AgentPosition.x, AgentPosition.y);
	
  //now transform the vertices
  matTransform.TransformVector2Ds(TransPoint);

  return TransPoint;
}

i tryed to do it (with the irrlicht matrix) like this

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	core::vector3df PointToWorldSpace(	core::vector3df point,
										core::vector3df agentHeading,
										core::vector3df agentSide,
										core::vector3df agentPosition )
	{
		core::vector3df TPoint = point;
		core::CMatrix4<float> transformMatrix;
		transformMatrix.rotateVect(agentHeading,agentSide);

		transformMatrix.translateVect(agentPosition);
		transformMatrix.transformVect(TPoint);
		return TPoint;
	}

(there should only be a rotation on the z-axis ) ...

but the problem is thet somthing dont work correct ... TPoint is always the same like point ... does someone knows what dosn't works ?

regards zeus

[Acki]

you create a new matrix, so everything is initialised to 0 by default for it:

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core::CMatrix4<float> transformMatrix;

you rotate agentSide by the matrix (still everything is 0 for the matrix) and return it by agentHeading, so no changes to agentSide, but agentHeading gets the same value as agentSide:

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transformMatrix.rotateVect(agentHeading,agentSide);

then you translate agentPosition by the matrix (still everything is 0 for the matrix):

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transformMatrix.translateVect(agentPosition);

and finally you transform TPoint by the matrix (still everything is 0 for the matrix)

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transformMatrix.transformVect(TPoint);

I hope you see that TPoint can't be changed, because the matrix has set all values to defaults (0) for the whole function !!!