Qt viewport and window

The drawing device is the physical coordinates of the basic coordinate system can be obtained more easily coordinate the logical operation by translation and rotation transformation QPainter

Viewport: drawing apparatus of any physical coordinates of a rectangular area, you can select only the physical coordinates of a rectangular area for drawing. The default viewport entire rectangular region is equal to the case where the drawing device.

            QPaintset :: setViewport (int x, int y, int width, int height) defined viewport

Window: viewport corresponding to the rectangular area, but is a coordinate system defined by the logical coordinates, rectangular coordinates of the center of the central window

           QPaintset::setWindow(int x , int y, int width ,int height)

 

 1 #include "viewport.h"
 2 #include "ui_viewport.h"
 3 #include <QPainter>
 4 #include <QPen>
 5 #include <QBrush>
 6 #include <QtMath>
 7 #include <QLinearGradient>
 8 viewport::viewport(QWidget *parent) :
 9     QWidget(parent),
10     ui(new Ui::viewport)
11 {
12     ui->setupUi(this);
13     setWindowTitle("视口和窗口");
14 }
15 
16 viewport::~viewport()
17 {
18     delete ui;
19 }
20 
21 void viewport::paintEvent(QPaintEvent *event)
22 {
23     QPainter painter(this);
24     int w = width();
25     int h = height();
26     int side = qMin(w,h);
27     QRect rect((w-side)/2,(h-side)/2,side,side);
28     painter.drawRect(rect);
29      painter.setViewport (RECT);             // Set the ViewPort 
30      painter.setWindow (- 100 , - 100 , 200 is , 200 is ); // set the coordinate window logic 
31 is      painter.setRenderHint (QPainter :: Antialiasing);
 32  
33 is      QPen PEN;
 34 is      pen.setWidth ( 2 );
 35      pen.setColor (the Qt :: Red);
 36      pen.setStyle (the Qt :: SolidLine);
 37 [      painter.setPen (PEN);
 38 is  
39      qlineargradient linerGrad ( 0 , 0 , 100,0);
40     linerGrad.setColorAt(0,Qt::yellow);
41     linerGrad.setColorAt(1,Qt::green);
42     linerGrad.setSpread(QGradient::PadSpread);
43     painter.setBrush(linerGrad);
44 
45     //设置复合模式
46     painter.setCompositionMode(QPainter::RasterOp_SourceXorDestination);
47 
48     for(int i = 0 ; i < 36 ; i++)
49     {
50         painter.drawEllipse(QPoint(50,0), 50 , 50 );
 51 is          painter.rotate ( 10 );    // after drawing the circle a 10 degree rotation of the coordinate system 
52 is  
53 is      }
 54 }

Different parameters can obtain different superposed FIG.