Correction to the documentation: https://doc.qt.io/qt-5/qtransform.html#basic-matrix-operations

User has a request about the documentation: https://doc.qt.io/qt-5/qtransform.html#basic-matrix-operations

"

The documentation above is not fully correct. For example

the table (https://doc.qt.io/qt-5/images/qtransform-representation.png) should read more like:

| m11 m12 m13 (dx)|
| m21 m22 m23 (dy)|
|.............|

and the black box below it should read:

x' = m11*x + m12*y + m13 (dx)
........

eg for a rotation (angle t) followed by a translation

| Cos(t) Sin(t) | . | x | + |dx|
| -Sin(t) Cos(t) | | y | + |dy|

ie x' = Cos(t) . x + Sin(t) . y + dx
etc

ie for a rotation of 45 degrees, the coefficient of y is +.7 (not -.7)
and this can be seen to be QTransfrom.12():

QTransform Tr;
Tr.rotate(45);
qreal c1 = Tr.m12(); // +.707
qreal c2 = Tr.m21(); // -.707

Furthermore, the text between the two eg "The m11 and m22 elements specify horizontal and vertical scaling"
is inaccurate. m11 and m22 do not simply represent the scaling. Its more complicated than this for a general (composite) transformation.
It would be more accurate to say that eg in the case of a pure scale do these represent the components of the scale.

Similarly "The m31 (dx) and m32 (dy) elements specify horizontal and vertical translation" is not true in general (apart fomr the fact that m31 -> m13 and m32 -> m23)
eg a translation followed by a rotation, see above, is not the same as vice-versa. The latter would be

| Cos(t) Sin(t) | . | x + dx |
| -Sin(t) Cos(t) | | y + dy |

ie x' = Cos(t) . (x + dx) + Sin(t) . (y + dy)
= Cos(t) . x + Cos(t) . dx + Sin(t) . y + Sin(t) . dy
= Cos(t) . x + Sin(t) . y + ((Cos(t) . dx) + Sin(t) . dy))
ie m13 = (Cos(t) . dx) + (Sin(t) . dy)
and thus not simply
m13 = dx

"