Qt Coordinate System

Coordinate Transformation

world corrdinates	=>	window coordinates	=>	device coordinates
( logical coordinate )	world change	intermediate state coordinate	window view transformation	( physical coordinate )

By default,3Coordinate Systems are consistent.

World change

Functions directly related to world transformations:

Qpainter: setworldmatrixenabled	Enable or disable world Transform
Qpainter: setworldtransform	Set world change
Qpainter: worldtransform	Get current
Qpainter: resettransform	ResetQtransform ()

4Common functions

Qpainter: Translate	Translation
Qpainter: Scale	Zoom
Qpainter: Rotate	Rotate
Qpainter: Shear	Cut

Note: they are directly calledQtransformDirectly modify the world change

Void qpainter: Scale (qreal Sx, qreal SY)
{
...
D-> state-> worldmatrix. Scale (sx, Sy );
...
}

Two world-changing vests:

Qpainter: settransform

Qpainter: Transform

Void qpainter: settransform (const qtransform & transform, bool combine)

{
Setworldtransform (transform, combine );

}

Obsolete Functions(SlaveQt4.3Start,QtransformReplacedQmatrixIs not recommended for the following functions):

Qpainter: setworldmatrix

Qpainter: worldmatrix

...

Window-view Transformation

Direct correlation:

Qpainter: setviewtransformenabled	Enable or disable the view transform function
Qpainter: viewtransformenabled	Returns the status of the viewport transform.
Qpainter: setviewport	Set the viewport (physical coordinates)
Qpainter: setwindow	Set the window (the same rectangle and intermediate state coordinates as the viewport)

This transformation is a simple linear transformation.

Compound Transformation

Combination of window-view transformation and world Transformation:

Qpainter: combinedtransform

Qtransform qpainter: combinedtransform () const

{
Q_d (const qpainter );
Return D-> state-> worldmatrix * D-> viewtransform ();

}

Typical application: converts coordinates from physical coordinatesQpainterRequired logical coordinates

Affine Transformation and transmission Transformation

Qt4.3 (Including)PreviousQmatrixOnly supports Affine Transformation(Affine transformation).

Translation(Translation)

Zoom (Scale)

Rotate (Rotation)

Cut(Shear)

QtransformTransmission transformation supported(Perspective transformation).

M11	M12	M13
M21	M22	M23
M31 DX	M32 Dy	M33

Conversion Relationship:

X' = M11 * x + m21 * Y + dx
Y' = m22 * Y + M12 * x + dy
If (is not affine)

{
W' = M13 * x + M23 * Y + M33
X'/= W'
Y'/= W'

}

 

Related Knowledge:

Projection Geometry, affine geometry, and differential geometry

Reference

Http://doc.qt.nokia.com/4.7/qtransform.html

Http://doc.qt.nokia.com/4.7/qpainter.html

Http://doc.qt.nokia.com/4.7/coordsys.html