QMatrix4x4 and OpenGL

NorskQt

Hi,

I have two simple questions related to QMatrix4x4 :

Is this matrix OpenGL compliant? If not, is there an easy way converting it to OpenGL matrix (float array of dimesion 16)?
How is this matrix indexed, usual C/C++ notation starting from zero, eg Qmatrix4x4 m(0,0) = refers to the first element in the matrix row : 0 and column : 0)?

Thanks!

Immii

QMatrix4x4 is transformation matrix in 3D space so you can use it where ever you want.

NorskQt

Immii,

You sound like you have not been working with 3D graphics.

Any qualified answer, please?

Thanks.

dangelog

[quote author="NorskQt" date="1293299650"]Hi,

I have two simple questions related to QMatrix4x4 :

Is this matrix OpenGL compliant? If not, is there an easy way converting it to OpenGL matrix (float array of dimesion 16)?
How is this matrix indexed, usual C/C++ notation starting from zero, eg Qmatrix4x4 m(0,0) = refers to the first element in the matrix row : 0 and column : 0)?

Thanks![/quote]

Unfortunately, QMatrix4x4 is a matrix of 16 qreals, which may or may not be GL_FLOAT -- and usually they are not, since qreal is double everywhere except on ARM, and GL_FLOAT is float everywhere. Qt uses some internal macros to do the job: see for instance
http://qt.gitorious.com/qt/qt/blobs/master/src/opengl/qglshaderprogram.cpp#line2188

Apart from this, internally QMatrix4x4 is a qreal[ 4 ][ 4 ] packed in column-major order (i.e. operator()(x, y) will assign to data[y][x], matching OpenGL), so the first element is indeed (0, 0).

NorskQt

Hi Peppe,

Thank you very much for providing information about QMatrix4x4. It's a kind of strange though because Qt works with OpenGL and Qt's 3D-graphics matrix is not OpenGL compliant. This is something that the Qt developers should consider.

Thank you very much again.

bbuerger

Hi there,

correct my if I'm wrong but opengl can be used with floats.
Just use gl...d instead of the gl...f in these case glLoadMatrixd

Greetings,
bbuerger