3x3 View Matrix with Marmalade

Question

I have been stuck on a problem for a few hours now. I need to convert my 4x4 matrices (Model, View, Projection) to 3x3 matrices with a translation vector. I need to do this because the API I am using has no 4x4 matrix class and its fully closed source.

The strange thing is that their LookAt function states that it does not affect the translation part of the matrix at all. Where as the 4x4 matrix I am using to render has it (Everything renders 100% correct).

Can someone please have a look at my conversion functions and see what I am doing wrong? Thanks

CIwFMat ConvertToMarmaladeFormat(Matrix4& Mat)
{
    CIwFMat M;

    M.m[0][0] = Mat[0][0];
    M.m[0][1] = Mat[0][1];
    M.m[0][2] = Mat[0][2];

    M.m[1][0] = Mat[1][0];
    M.m[1][1] = Mat[1][1];
    M.m[1][2] = Mat[1][2];

    M.m[2][0] = Mat[2][0];
    M.m[2][1] = Mat[2][1];
    M.m[2][2] = Mat[2][2];

    M.t = CIwFVec3(Mat[3][0], Mat[3][1], Mat[3][2]);

    return M;
}

Matrix4 ConvertFromMarmaladeFormat(CIwFMat& M)
{
    Matrix4 Mat;
    Mat.identity();

    Mat[0][0] = M.m[0][0];
    Mat[0][1] = M.m[0][1];
    Mat[0][2] = M.m[0][2];

    Mat[1][0] = M.m[1][0];
    Mat[1][1] = M.m[1][1];
    Mat[1][2] = M.m[1][2];

    Mat[2][0] = M.m[2][0];
    Mat[2][1] = M.m[2][1];
    Mat[2][2] = M.m[2][2];

    Mat[3][0] = M.t.x;
    Mat[3][1] = M.t.y;
    Mat[3][2] = M.t.z;

    return Mat;
}

class Matrix4
{
    friend Vector4 operator*(const Vector4 &lhs, const Matrix4 &rhs);
    friend Vector3 operator*(const Vector3 &lhs, const Matrix4 &rhs);
    friend Matrix4 operator*(float scalar, const Matrix4 &rhs);

public:
    static const Matrix4 IDENTITY;
    static Matrix4 createFromAxes(const Vector3 &x, const Vector3 &y, const Vector3 &z);
    static Matrix4 createFromAxesTransposed(const Vector3 &x, const Vector3 &y, const Vector3 &z);
    static Matrix4 createFromHeadPitchRoll(float headDegrees, float pitchDegrees, float rollDegrees);
    static Matrix4 createMirror(const Vector3 &planeNormal, const Vector3 &pointOnPlane);
    static Matrix4 createOrient(const Vector3 &from, const Vector3 &to);
    static Matrix4 createRotate(const Vector3 &axis, float degrees);
    static Matrix4 createScale(float sx, float sy, float sz);
    static Matrix4 createTranslate(float tx, float ty, float tz);

    Matrix4() {}
    Matrix4(float m11, float m12, float m13, float m14,
            float m21, float m22, float m23, float m24,
            float m31, float m32, float m33, float m34,
            float m41, float m42, float m43, float m44);
    ~Matrix4() {}

    float *operator[](int row);
    const float *operator[](int row) const;

    bool operator==(const Matrix4 &rhs) const;
    bool operator!=(const Matrix4 &rhs) const;

    Matrix4 &operator+=(const Matrix4 &rhs);
    Matrix4 &operator-=(const Matrix4 &rhs);
    Matrix4 &operator*=(const Matrix4 &rhs);
    Matrix4 &operator*=(float scalar);
    Matrix4 &operator/=(float scalar);

    Matrix4 operator+(const Matrix4 &rhs) const;
    Matrix4 operator-(const Matrix4 &rhs) const;
    Matrix4 operator*(const Matrix4 &rhs) const;
    Matrix4 operator*(float scalar) const;
    Matrix4 operator/(float scalar) const;

    float determinant() const;
    void fromAxes(const Vector3 &x, const Vector3 &y, const Vector3 &z);
    void fromAxesTransposed(const Vector3 &x, const Vector3 &y, const Vector3 &z);
    void fromHeadPitchRoll(float headDegrees, float pitchDegrees, float rollDegrees);
    void identity();
    Matrix4 inverse() const;
    void orient(const Vector3 &from, const Vector3 &to);
    void rotate(const Vector3 &axis, float degrees);
    void scale(float sx, float sy, float sz);
    void toAxes(Vector3 &x, Vector3 &y, Vector3 &z) const;
    void toAxesTransposed(Vector3 &x, Vector3 &y, Vector3 &z) const;
    void toHeadPitchRoll(float &headDegrees, float &pitchDegrees, float &rollDegrees) const;
    void translate(float tx, float ty, float tz);
    Matrix4 transpose() const;

private:
    float mtx[4][4];
};

class CIwFMat
{
public:
/**
 * 3x3 rotation matrix.
 */
    float   m[3][3];
/**
 * Trans vector.
 */
    CIwFVec3    t;

...

};

You are assuming that both matrices are stored as [column][row]. Is that actually the case? If either of them is [row][column] then your conversion will fail. But if both are [col][row] then the code looks OK. Are both conversion failing or just one? — ChrisF
Well stuff just isn't rendering correctly. I am suprised that marmalade are using 3x3 matrices without any support for 4x4 ones. I read that projection matrix cant be less than 4x4 as well :( — Kachinsky
@user1040769: Without more info I don't think we can hope to help you. Are you sure your view matrix is correct in the first place, for example? — Goz
Its worth bearing in mind, for example, that a view matrix is NOT a look-at matrix its actually the inverse of a look-at matrix. My guess is that you are notting inverting it or that marmalade is inverting it for you ... — Goz

sanperrier sanperrier · Accepted Answer · 2013-10-01T16:56:31

Your transformation looks ok, but check that:

Marmalade uses row-column matrix notation, and right-handed axis system (bear it in mind with your transformations)

marmalade "view" matrix isn't actually a view matrix, it's camera position and orientation matrix. To get actual view matrix one should do smth like this:

CIwFMat MarmaladeView = IwGxGetViewMatrix();
CIwFMat view = (CIwFMat(CIwFMat::g_Identity, -MarmaladeView.GetTrans()) * MarmaladeView.GetTranspose()); // actually it's simple matrix inversion, but CIwFMat doesn't have Inverse() method
// in some cases your should add axis-flip transform

marmalade IwGxGetPerspectiveMatrix() returns invalid projection matrix in case of Ortographic projection (documentation says nothing about that interesting fact)
LookAt() function simply sets rotation part of matrix to match the direction between 2 points, so do the translation manually
check your far/near planes

All MVP matrices should be explicitly set by

IwGxSetViewMatrix(); // sets view matrix view - camera position
IwGxSetModelMatrix(); // sets model matrix
IwGxSetPerspMul(); // sets perspective projection in terms of distance to view plane
IwGxSetFarZNearZ(); // sets clipping planes

3x3 View Matrix with Marmalade

1 Answers