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：

1. #include<QtGui/QApplication>
2. #include"gradient_test.h"
3. intmain(intargc,char*argv[])
4. {
5. QApplicationa(argc,argv);
6. gradient_testw;
7. w.show();
8. returna.exec();
9. }
10. //gradient_test.h:
11. #ifndefGRADIENT_TEST_H
12. #defineGRADIENT_TEST_H
13. #include<QtGui/QWidget>
14. #include<QPainter>
15. #include<QStyleOption>
16. #include<QResizeEvent>
17. classgradient_test:publicQWidget
18. {
19. Q_OBJECT
20. public:
21. explicitgradient_test(QWidget*parent=0);
22. virtualQSizesizeHint()const;
23. protected:
24. voidpaintEvent(QPaintEvent*event);
25. voidresizeEvent(QResizeEvent*event);
26. private:
27. QSizeinitSize;
28. QImagewheel;
29. voiddrawLine(constQSize&newSize);
30. };
31. #endif//GRADIENT_TEST_H
32. //gradient_test.cpp:
33. #include"gradient_test.h"
34. gradient_test::gradient_test(QWidget*parent)
35. :QWidget(parent),initSize(300,300)
36. {
37. resize(650,250);    //窗口大小
38. }
39. voidgradient_test::drawLine(constQSize&newSize)
40. {
41. QPainterpainter(&wheel);   //wheel作为画图对象？
42. painter.setRenderHint(QPainter::Antialiasing);  //消除锯齿
43. wheel.fill(Qt::white);
44. //线性渐变
45. QLinearGradientlinearGradient(20,20,150,150);
46. //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
47. //painter.setPen(Qt::NoPen);
48. linearGradient.setColorAt(0.0,Qt::green);
49. linearGradient.setColorAt(0.2,Qt::white);
50. linearGradient.setColorAt(0.4,Qt::blue);
51. linearGradient.setColorAt(0.6,Qt::red);
52. linearGradient.setColorAt(1.0,Qt::yellow);
53. painter.setBrush(QBrush(linearGradient));
54. painter.drawEllipse(10,10,200,200);
55. //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
56. //辐射渐变
57. QRadialGradientradialGradient(310,110,100,310,110);
58. //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
59. radialGradient.setColorAt(0,Qt::green);
60. //radialGradient.setColorAt(0.2,Qt::white);
61. radialGradient.setColorAt(0.4,Qt::blue);
62. //radialGradient.setColorAt(0.6,Qt::red);
63. radialGradient.setColorAt(1.0,Qt::yellow);
64. painter.setBrush(QBrush(radialGradient));
65. painter.drawEllipse(210,10,200,200);//在相应的坐标画出来
66. //弧度渐变
67. QConicalGradientconicalGradient(510,110,0);
68. //创建了一个QConicalGradient对象实例，参数分别为中心坐标和初始角度
69. conicalGradient.setColorAt(0,Qt::green);
70. conicalGradient.setColorAt(0.2,Qt::white);
71. conicalGradient.setColorAt(0.4,Qt::blue);
72. conicalGradient.setColorAt(0.6,Qt::red);
73. conicalGradient.setColorAt(0.8,Qt::yellow);
74. conicalGradient.setColorAt(1.0,Qt::green);
75. //设置渐变的颜色和路径比例
76. painter.setBrush(QBrush(conicalGradient));
77. painter.drawEllipse(410,10,200,200);//在相应的坐标画出来
78. }
79. QSizegradient_test::sizeHint()const
80. {
81. returnQSize(height(),height());
82. }
83. voidgradient_test::resizeEvent(QResizeEvent*event)
84. {
85. wheel=QImage(event->size(),QImage::Format_ARGB32_Premultiplied);
86. wheel.fill(palette().background().color());
87. drawLine(event->size());
88. update();
89. }
90. voidgradient_test::paintEvent(QPaintEvent*event)
91. {
92. QPainterpainter(this);
93. QStyleOptionopt;
94. opt.init(this);
95. painter.drawImage(0,0,wheel);
96. style()->drawPrimitive(QStyle::PE_Widget,&opt,&painter,this);
97. }

#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);
}