QT 学习记录：渐变-QLinearGradient，QRadialGradient，QConicalGradient)

http://blog.csdn.net/wangwei890702/article/details/8552482

QT：渐变

渐变，是指逐渐的，有规律性的变化,是一种规律性很强的现象。Qt提供了一个与渐变相关的QGradient类，目前支持三种渐变画刷，分别是线性渐变(QLinearGradient)、辐射渐变(QRadialGradient)、角度渐变(QConicalGradient)，如下图所示：

从左到右依次为：线性渐变、辐射渐变、角度渐变

下面来看一下实现的代码，由于程序较简单，所以将解释都加在了每行代码的后边：



[cpp]
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#include<QtGui/QApplication>

#include"gradient_test.h"
intmain(intargc,char*argv[])
{
QApplicationa(argc,argv);
gradient_testw;
w.show();
returna.exec();
}
//gradient_test.h:
#ifndefGRADIENT_TEST_H

#defineGRADIENT_TEST_H
#include<QtGui/QWidget>

#include<QPainter>
#include<QStyleOption>

#include<QResizeEvent>
classgradient_test:publicQWidget
{
Q_OBJECT
public:
explicitgradient_test(QWidget*parent=0);
virtualQSizesizeHint()const;
protected:
voidpaintEvent(QPaintEvent*event);
voidresizeEvent(QResizeEvent*event);
private:
QSizeinitSize;
QImagewheel;
voiddrawLine(constQSize&newSize);
};
#endif//GRADIENT_TEST_H

//gradient_test.cpp:
#include"gradient_test.h"

gradient_test::gradient_test(QWidget*parent)
:QWidget(parent),initSize(300,300)
{
resize(650,250); //窗口大小

}
voidgradient_test::drawLine(constQSize&newSize)
{
QPainterpainter(&wheel); //wheel作为画图对象？

painter.setRenderHint(QPainter::Antialiasing); //消除锯齿

wheel.fill(Qt::white);
//线性渐变
QLinearGradientlinearGradient(20,20,150,150);
//创建了一个QLinearGradient对象实例，参数为起点和终点坐标，可作为颜色渐变的方向

//painter.setPen(Qt::NoPen);

linearGradient.setColorAt(0.0,Qt::green);
linearGradient.setColorAt(0.2,Qt::white);
linearGradient.setColorAt(0.4,Qt::blue);
linearGradient.setColorAt(0.6,Qt::red);
linearGradient.setColorAt(1.0,Qt::yellow);
painter.setBrush(QBrush(linearGradient));
painter.drawEllipse(10,10,200,200);
//前面为左边，后面两个参数为横轴和纵轴,上面的四行分别设置渐变的颜色和路径比例

//辐射渐变
QRadialGradientradialGradient(310,110,100,310,110);
//创建了一个QRadialGradient对象实例，参数分别为中心坐标，半径长度和焦点坐标,如果需要对称那么中心坐标和焦点坐标要一致

radialGradient.setColorAt(0,Qt::green);
//radialGradient.setColorAt(0.2,Qt::white);

radialGradient.setColorAt(0.4,Qt::blue);
//radialGradient.setColorAt(0.6,Qt::red);

radialGradient.setColorAt(1.0,Qt::yellow);
painter.setBrush(QBrush(radialGradient));
painter.drawEllipse(210,10,200,200);//在相应的坐标画出来

//弧度渐变
QConicalGradientconicalGradient(510,110,0);
//创建了一个QConicalGradient对象实例，参数分别为中心坐标和初始角度

conicalGradient.setColorAt(0,Qt::green);
conicalGradient.setColorAt(0.2,Qt::white);
conicalGradient.setColorAt(0.4,Qt::blue);
conicalGradient.setColorAt(0.6,Qt::red);
conicalGradient.setColorAt(0.8,Qt::yellow);
conicalGradient.setColorAt(1.0,Qt::green);
//设置渐变的颜色和路径比例
painter.setBrush(QBrush(conicalGradient));
painter.drawEllipse(410,10,200,200);//在相应的坐标画出来

}
QSizegradient_test::sizeHint()const
{
returnQSize(height(),height());
}
voidgradient_test::resizeEvent(QResizeEvent*event)
{
wheel=QImage(event->size(),QImage::Format_ARGB32_Premultiplied);
wheel.fill(palette().background().color());
drawLine(event->size());
update();
}
voidgradient_test::paintEvent(QPaintEvent*event)
{
QPainterpainter(this);
QStyleOptionopt;
opt.init(this);
painter.drawImage(0,0,wheel);
style()->drawPrimitive(QStyle::PE_Widget,&opt,&painter,this);
}

#include<QtGui/QApplication>
#include"gradient_test.h"
intmain(intargc,char*argv[])
{
QApplicationa(argc,argv);
gradient_testw;
w.show();
returna.exec();
}
//gradient_test.h:
#ifndefGRADIENT_TEST_H
#defineGRADIENT_TEST_H
#include<QtGui/QWidget>
#include<QPainter>
#include<QStyleOption>
#include<QResizeEvent>
classgradient_test:publicQWidget
{
Q_OBJECT
public:
explicitgradient_test(QWidget*parent=0);
virtualQSizesizeHint()const;
protected:
voidpaintEvent(QPaintEvent*event);
voidresizeEvent(QResizeEvent*event);
private:
QSizeinitSize;
QImagewheel;
voiddrawLine(constQSize&newSize);
};
#endif//GRADIENT_TEST_H

//gradient_test.cpp:
#include"gradient_test.h"
gradient_test::gradient_test(QWidget*parent)
:QWidget(parent),initSize(300,300)
{
resize(650,250);    //窗口大小
}
voidgradient_test::drawLine(constQSize&newSize)
{
QPainterpainter(&wheel);   //wheel作为画图对象？
painter.setRenderHint(QPainter::Antialiasing);  //消除锯齿
wheel.fill(Qt::white);
//线性渐变
QLinearGradientlinearGradient(20,20,150,150);
//创建了一个QLinearGradient对象实例，参数为起点和终点坐标，可作为颜色渐变的方向
//painter.setPen(Qt::NoPen);
linearGradient.setColorAt(0.0,Qt::green);
linearGradient.setColorAt(0.2,Qt::white);
linearGradient.setColorAt(0.4,Qt::blue);
linearGradient.setColorAt(0.6,Qt::red);
linearGradient.setColorAt(1.0,Qt::yellow);
painter.setBrush(QBrush(linearGradient));
painter.drawEllipse(10,10,200,200);
//前面为左边，后面两个参数为横轴和纵轴,上面的四行分别设置渐变的颜色和路径比例

//辐射渐变
QRadialGradientradialGradient(310,110,100,310,110);
//创建了一个QRadialGradient对象实例，参数分别为中心坐标，半径长度和焦点坐标,如果需要对称那么中心坐标和焦点坐标要一致
radialGradient.setColorAt(0,Qt::green);
//radialGradient.setColorAt(0.2,Qt::white);
radialGradient.setColorAt(0.4,Qt::blue);
//radialGradient.setColorAt(0.6,Qt::red);
radialGradient.setColorAt(1.0,Qt::yellow);
painter.setBrush(QBrush(radialGradient));
painter.drawEllipse(210,10,200,200);//在相应的坐标画出来
//弧度渐变
QConicalGradientconicalGradient(510,110,0);
//创建了一个QConicalGradient对象实例，参数分别为中心坐标和初始角度
conicalGradient.setColorAt(0,Qt::green);
conicalGradient.setColorAt(0.2,Qt::white);
conicalGradient.setColorAt(0.4,Qt::blue);
conicalGradient.setColorAt(0.6,Qt::red);
conicalGradient.setColorAt(0.8,Qt::yellow);
conicalGradient.setColorAt(1.0,Qt::green);
//设置渐变的颜色和路径比例
painter.setBrush(QBrush(conicalGradient));
painter.drawEllipse(410,10,200,200);//在相应的坐标画出来
}
QSizegradient_test::sizeHint()const
{
returnQSize(height(),height());
}
voidgradient_test::resizeEvent(QResizeEvent*event)
{
wheel=QImage(event->size(),QImage::Format_ARGB32_Premultiplied);
wheel.fill(palette().background().color());
drawLine(event->size());
update();
}
voidgradient_test::paintEvent(QPaintEvent*event)
{
QPainterpainter(this);
QStyleOptionopt;
opt.init(this);
painter.drawImage(0,0,wheel);
style()->drawPrimitive(QStyle::PE_Widget,&opt,&painter,this);
}