一、坐标系统与坐标变换
坐标系统
QPainter坐标变换相关函数
| 分组 |
函数原型 |
功能 |
| 坐标变换 |
void translate(qreal dx,qreal dy) |
坐标系统一定的偏移量，坐标原点平移到新的点 |
| void rotate(qreal angle) |
坐标系统顺时针旋转-一个角度 |
| void scale(qreal sx,qreal sy) |
坐标系统缩放 |
| void shear(qrael sh,qreal sy) |
坐标系统做扭转变换 |
| 状态保存与恢复 |
void save() |
保存painter当前的状态，就是将当前状态压入栈 |
| void restore() |
恢复上一次状态，就是从堆栈中弹出上次的状态 |
| void resetTransform() |
复位所有的坐标变换 |
示例
绘制五角星
船舰widget窗口，只重载paintEvent函数
#include "widget.h"
#include "ui_widget.h"
#include
#include
#include
Widget::Widget(QWidget *parent)
: QWidget(parent)
, ui(new Ui::Widget)
{
ui->setupUi(this);
setPalette(QPalette(Qt::white));
setAutoFillBackground(true);
resize(600,300);
}
Widget::~Widget()
{
delete ui;
}
void Widget::paintEvent(QPaintEvent *event)
{
Q_UNUSED(event);
QPainter painter(this);
QPen pen; //笔
pen.setStyle(Qt::SolidLine);
painter.setPen(pen);
painter.setRenderHint(QPainter::Antialiasing); //抗锯齿
QBrush brush; //刷子
brush.setColor(Qt::yellow);
brush.setStyle(Qt::SolidPattern);
painter.setBrush(brush);
//qreal deg = 3.141592*2/5;
qreal deg = (360/5)*3.141592/180;
qreal R=100;
QPoint points[5] = {
QPoint(R,0),
QPoint(R*std::cos(deg),-R*std::sin(deg)),
QPoint(R*std::cos(2*deg),-R*std::sin(2*deg)),
QPoint(R*std::cos(3*deg),-R*std::sin(3*deg)),
QPoint(R*std::cos(4*deg),-R*std::sin(4*deg)),
};
QPainterPath starPath;
starPath.moveTo(points[3]);
starPath.lineTo(points[1]);
starPath.lineTo(points[4]);
starPath.lineTo(points[2]);
starPath.lineTo(points[0]);
starPath.closeSubpath();
QFont font;
font.setPointSize(12);
starPath.addText(points[0], font, "0");
starPath.addText(points[1], font, "1");
starPath.addText(points[2], font, "2");
starPath.addText(points[3], font, "3");
starPath.addText(points[4], font, "4");
painter.setFont(font);
painter.save(); //保存
painter.translate(100,120);
painter.drawPath(starPath);
painter.drawText(0,0,"S1");
painter.restore(); //恢复
painter.translate(300,120);
painter.rotate(90);
painter.scale(0.7,0.7);
painter.drawPath(starPath);
painter.drawText(0,0,"S2");
painter.resetTransform();
painter.translate(500,120);
painter.rotate(-90);
painter.scale(1.05,1.05);
painter.drawPath(starPath);
painter.drawText(0,0,"S3");
}
二、可缩放图形
视口: 绘图设备的任意一个矩形区域的物理坐标，可以只选取物理坐标的一个矩形区域用
于绘图。视口默认情况下等于绘图设备的整个矩形区。
窗口: 对应于视口的矩形区域，只不过是用逻辑坐标定义的坐标系，窗口坐标的中心在矩
形中心。
使用窗口坐标绘制，不用管实际的物理大小
#include "widget.h"
#include "ui_widget.h"
#include
#include
#include
Widget::Widget(QWidget *parent)
: QWidget(parent)
, ui(new Ui::Widget)
{
ui->setupUi(this);
setPalette(QPalette(Qt::white));
setAutoFillBackground(true);
resize(300,300);
}
Widget::~Widget()
{
delete ui;
}
void Widget::paintEvent(QPaintEvent *event)
{
Q_UNUSED(event);
QPainter painter(this);
painter.setRenderHint(QPainter::Antialiasing);
int W = QWidget::width();
int H = QWidget::height();
int side = qMin(W,H);
QRect rect((W-side)/2,(H-side)/2, side,side); //视口大小
painter.drawRect(rect);
painter.setViewport(rect);
painter.setWindow(-100,-100,200,200);
QLinearGradient linerGradient(0,0,100,0); // 渐变
linerGradient.setColorAt(0,Qt::yellow);
linerGradient.setColorAt(1,Qt::green);
linerGradient.setSpread(QGradient::PadSpread); //发散
painter.setCompositionMode(QPainter::RasterOp_NotSourceXorDestination);
painter.setBrush(linerGradient);
for (size_t i=0; i<36; i++) {
painter.drawEllipse(QPoint(50,0),50,50);
painter.rotate(10);
}
}
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