Details

Type: Suggestion

Status: Reported

Priority: P3: Somewhat important

Resolution: Unresolved

Affects Version/s: 5.15.2, 6.0.0

Fix Version/s: None

Component/s: GUI: OpenGL, GUI: Painting

Labels:None
Description
QVector3D documentation says `"The QVector3D class represents a vector or vertex in 3D space." `
QMatrix4x4 provides an operator* to transform a QVector3D. This has several issues:
 Using * remembers of an algebraic operation, which is incorrect between a 4x4 matrix and a 3x1 vector. This is implement as if the QVeector3D was a QVector4D with a 1 in the w coordinate and doing the mathematical operation.
 By doing that, it fails the purpose of QVector3D being a vector or a vertex, since its always considered a vertex. You can't consider a vector because when transforming it with a QMatrix4x4 its going to be treated as a vertex.
 Thee operator* remembers of the algebraic operation, so one could think that the distributive property applies, but it doesnt.
Consider the following code:
QMatrix4x4 worldMatrix; QVector3D p; worldMatrix * p  worldMatrix * QVector3D(0,0,0);
p here is a vector, so when applying the worldMatrix transformation, I dont wan't the traslation. That is why I need to remove it with the `worldMatrix * QVector3D(0,0,0)`.
One could also consider that the code could be refactored as:
QMatrix4x4 worldMatrix;
QVector3D p;
worldMatrix * p; // in algebra, multiplying by a null vector returns a null vector
which doesn't give the same result.
I would suggest deprecating and removing all the non mathematical operations and use proper algebra for these operations.