qt实现图片缩放

/** * Author: lwei * Since: 2017.11.14 * Version: 1.0.0 */ #include "pixmapwidget.h" #include <QDebug> #include <QPainter> #include <QPaintEvent> #include <QWheelEvent> #include <QMatrix> #define DEFAULT_SCALE 1.0 #define MAX_SCALE 3.0 #define MIN_SCALE 0.5 #define MAX_ROTATE 360 #define MIN_ROTATE 0 #define DEFAULT_ROTATE 0 //鼠标滚轮的距离会在计算数字的时候乘以8 #define RATIO_TO_DOULBE (8 * 360) PixmapWidget::PixmapWidget(QWidget *parent) : QWidget(parent), m_pixmapPath(QString()), m_scale(DEFAULT_SCALE), m_rotationAngle(DEFAULT_ROTATE) { } QString PixmapWidget::pixmapPath() const { return m_pixmapPath; } void PixmapWidget::setPixmapPath(const QString &pixmapPath) { if(m_pixmapPath != pixmapPath) { m_pixmapPath = pixmapPath; m_scale = DEFAULT_SCALE; m_rotationAngle = DEFAULT_ROTATE; } } int PixmapWidget::rotationAngle() const { return m_rotationAngle; } void PixmapWidget::setRotationAngle(int rotationAngle) { m_rotationAngle = rotationAngle; } void PixmapWidget::execScale(bool scaleFalg, double scale) { if(scaleFalg) { m_scale += scale; } else { m_scale -= scale; } limitScale(); update(); } void PixmapWidget::execRotate(int rotateSize) { m_rotationAngle += rotateSize; while(m_rotationAngle < MIN_ROTATE || m_rotationAngle > MAX_ROTATE) { if(m_rotationAngle < MIN_ROTATE) { m_rotationAngle += MAX_ROTATE; } if(m_rotationAngle > MAX_ROTATE) { m_rotationAngle -= MAX_ROTATE; } } update(); } void PixmapWidget::paintEvent(QPaintEvent *event) { QPixmap pixmap; pixmap.load(m_pixmapPath); QMatrix matrix; matrix.rotate(m_rotationAngle); pixmap = pixmap.transformed(matrix, Qt::FastTransformation); int pixmapWidth = pixmap.width(); int pixmapHeight = pixmap.height(); QPoint widgetStartPos = this->pos(); int painterWidth = pixmapWidth * m_scale; int painterHeight = pixmapHeight * m_scale; int widgetWidth = this->width(); int widgetHeight = this->height(); QPoint startPos(widgetStartPos.x() + widgetWidth/2 - painterWidth/2, widgetStartPos.y() + widgetHeight/2 - painterHeight/2); QPainter painter(this); painter.drawPixmap(QRect(startPos.x(), startPos.y(), painterWidth, painterHeight), pixmap); QWidget::paintEvent(event); } void PixmapWidget::wheelEvent(QWheelEvent *event) { int value = event->delta(); double scaleRatio = ((double)value)/RATIO_TO_DOULBE; m_scale += scaleRatio; limitScale(); update(); event->accept(); } void PixmapWidget::limitScale() { m_scale = m_scale > MAX_SCALE ? MAX_SCALE : (m_scale < MIN_SCALE ? MIN_SCALE : m_scale); }