(转)双缓冲技术1

xiaoxiao2021-02-28 101

(转)双缓冲技术1

标签： qtplotsignalvariablesscroll编程 2008-05-20 20:32 1960人阅读评论(0) 收藏举报本文章已收录于：分类： Qt（31）作者同类文章 X •(转)利用Qt的qmake创建vc工程 •(转)QT事件机制 •(转)QT中画图方法的不同 •(转)5.4 双缓冲技术(Double Buffering)-5 •(转)5.4 双缓冲技术(Double Buffering)-4 更多 Rubber band（橡皮筋线，或者橡皮线）， pixmap（图像，双缓冲中用到的图像，有时也直呼pixmap），off-screen pixmap（离线图像） Plot（plot，这一节实现的就是一个绘制曲线的控件Plotter，有时原文也叫plot，有点小名的意思，没有翻译，直接呼之）废话少说，以下是译文：双缓冲技术是GUI编程中常用的技术。所谓的双缓冲就是把把一个需要渲染的控件保存到一个离线图像（off-screen pixmap)中，然后再把图像拷贝到需要绘制的控件上。在Qt的早期版本中，为了用户界面更加清爽，经常用这个技术来消除闪烁。在Qt4中，QWidget能够自动处理闪烁，因此我们不用再担心这个问题。尽管如此，如果控件渲染复杂且需要经常刷新，双缓冲技术还是很有用的。我们可以把控件永久保存在一个图像中，随时准备下一次绘制事件的到来，一旦接到一个控件的绘制事件，就把图片拷贝到控件上。如果我们要做的只是小范围的修改，这个技术更是尤为有用，如要绘制一条橡皮筋线，就不必一次次刷新整个控件了。在本章的最后一节，我们实现的是一个叫做Plotter的自定义控件。这个控件使用了双缓冲技术，也涉及到了Qt编程的其他方面：如键盘的事件处理，布局和坐标系统。 Plotter控件用来显示一条或者多条曲线，这些曲线由一组向量坐标表示。用户可以在图像上画一个橡皮筋线(Rubeber band)，Plotter控件对橡皮筋线包围的区域进行放大。用户用鼠标左键在控件上选择一个点，然后拖动鼠标走到另一点，然后释放鼠标，就在控件上绘制一条橡皮筋线。 Figure 5.7 Zooming in on the Plotter Widget 用户可以多次用橡皮筋线进行放大，也可以用ZoomOut按钮缩小，然后用ZoomIn按钮再放大。ZoomOut和ZoomIn按钮只是在控件第一次放大或者缩小操作后变得可见，如果用户不缩放图形，则这两个按钮会一直不可见，这样可以使绘图区域不那么混乱。 Plotter控件可以存储任何数量的曲线的数据。同时它还维护一个PlotSettings对象的栈区域，每一个PlotSettings对象都是对应一个特定的缩放值。首先看一下头文件的代码(对头文件的解析在代码中用注释的形式给出)： #ifndef PLOTTER_H #define PLOTTER_H #include < QMap > // 包含的Qt的头文件 #include < QPixmap > #include < QVector > #include < QWidget > class QToolButton; // 两个前向声明 class PlotSettings; class Plotter : public QWidget { Q_OBJECT public : Plotter(QWidget * parent = 0 ); void setPlotSettings( const PlotSettings & settings); void setCurveData( int id, const QVector < QPointF > & data);//QPointF表明是浮点类型的QPoint void clearCurve( int id); QSize minimumSizeHint() const ; // 重写QWidget::minimumSizeHint() QSize sizeHint() const ; // 重写QWidget::sizeHint() public slots: void zoomIn(); // 放大曲线 void zoomOut(); // 缩小显示曲线 protected : // 重新实现的QWidget的事件处理函数 void paintEvent(QPaintEvent * event ); void resizeEvent(QResizeEvent * event ); void mousePressEvent(QMouseEvent * event ); void mouseMoveEvent(QMouseEvent * event ); void mouseReleaseEvent(QMouseEvent * event ); void keyPressEvent(QKeyEvent * event ); void wheelEvent(QWheelEvent * event ); private : void updateRubberBandRegion(); void refreshPixmap(); void drawGrid(QPainter * painter); void drawCurves(QPainter * painter); enum { Margin = 50 };//表明图象周围的空间 QToolButton * zoomInButton; QToolButton * zoomOutButton; QMap < int , QVector < QPointF > > curveMap; // 曲线数据 QVector < PlotSettings > zoomStack; // PlotSettings栈区域 int curZoom; bool rubberBandIsShown; QRect rubberBandRect; QPixmap pixmap; // 显示在屏幕的控件的一个拷贝，任何绘制总是先绘制在离线pixmap上，然后拷贝到控件上 }; // PlotSettings确定x，y轴的范围，和刻度的个数 class PlotSettings { public : PlotSettings(); void scroll( int dx, int dy); void adjust(); double spanX() const { return maxX - minX; } double spanY() const { return maxY - minY; } double minX; double maxX; int numXTicks; double minY; double maxY; int numYTicks; private : static void adjustAxis( double & min, double & max, int & numTicks); }; #endif 图5-8表示了Plotter控件和PlotSettings的关系。通常，numXTicks和numYTicks是有一个的误差，如果numXTicks为5，实际上Plotter会在x轴上绘制6个刻度。这样可以简化以后的计算（至于怎么样简化的，就看程序和后文吧）。 Figure 5-8 PlotSettings's member variables 现在来看源文件（代码有些长，先用代码格式给出完整源文件代码）： #include < QtGui > #include < cmath > #include " plotter.h " Plotter::Plotter(QWidget * parent) : QWidget(parent) { setBackgroundRole(QPalette::Dark); setAutoFillBackground( true ); setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding); setFocusPolicy(Qt::StrongFocus); rubberBandIsShown = false ; zoomInButton = new QToolButton( this ); zoomInButton -> setIcon(QIcon( " :/images/zoomin.png " )); zoomInButton -> adjustSize(); connect(zoomInButton, SIGNAL(clicked()), this , SLOT(zoomIn())); zoomOutButton = new QToolButton( this ); zoomOutButton -> setIcon(QIcon( " :/images/zoomout.png " )); zoomOutButton -> adjustSize(); connect(zoomOutButton, SIGNAL(clicked()), this , SLOT(zoomOut())); setPlotSettings(PlotSettings()); } void Plotter::setPlotSettings( const PlotSettings & settings) { zoomStack.clear(); zoomStack.append(settings); curZoom = 0 ; zoomInButton -> hide(); zoomOutButton -> hide(); refreshPixmap(); } void Plotter::zoomOut() { if (curZoom > 0 ) { -- curZoom; zoomOutButton -> setEnabled(curZoom > 0 ); zoomInButton -> setEnabled( true ); zoomInButton -> show(); refreshPixmap(); } } void Plotter::zoomIn() { if (curZoom < zoomStack.count() - 1 ) { ++ curZoom; zoomInButton -> setEnabled(curZoom < zoomStack.count() - 1 ); zoomOutButton -> setEnabled( true ); zoomOutButton -> show(); refreshPixmap(); } } void Plotter::setCurveData( int id, const QVector < QPointF > & data) { curveMap[id] = data; refreshPixmap(); } void Plotter::clearCurve( int id) { curveMap.remove(id); refreshPixmap(); } QSize Plotter::minimumSizeHint() const { return QSize( 6 * Margin, 4 * Margin); } QSize Plotter::sizeHint() const { return QSize( 12 * Margin, 8 * Margin); } void Plotter::paintEvent(QPaintEvent * /* event */ ) { QStylePainter painter( this ); painter.drawPixmap( 0 , 0 , pixmap); if (rubberBandIsShown) { painter.setPen(palette().light().color()); painter.drawRect(rubberBandRect.normalized() .adjusted( 0 , 0 , - 1 , - 1 )); } if (hasFocus()) { QStyleOptionFocusRect option; option.initFrom( this ); option.backgroundColor = palette().dark().color(); painter.drawPrimitive(QStyle::PE_FrameFocusRect, option); } } void Plotter::resizeEvent(QResizeEvent * /* event */ ) { int x = width() - (zoomInButton -> width() + zoomOutButton -> width() + 10 ); zoomInButton -> move(x, 5 ); zoomOutButton -> move(x + zoomInButton -> width() + 5 , 5 ); refreshPixmap(); } void Plotter::resizeEvent(QResizeEvent * /* event */ ) { int x = width() - (zoomInButton -> width() + zoomOutButton -> width() + 10 ); zoomInButton -> move(x, 5 ); zoomOutButton -> move(x + zoomInButton -> width() + 5 , 5 ); refreshPixmap(); } void Plotter::resizeEvent(QResizeEvent * /* event */ ) { int x = width() - (zoomInButton -> width() + zoomOutButton -> width() + 10 ); zoomInButton -> move(x, 5 ); zoomOutButton -> move(x + zoomInButton -> width() + 5 , 5 ); refreshPixmap(); } void Plotter::mousePressEvent(QMouseEvent * event ) { QRect rect(Margin, Margin, width() - 2 * Margin, height() - 2 * Margin); if ( event -> button() == Qt::LeftButton) { if (rect.contains( event -> pos())) { rubberBandIsShown = true ; rubberBandRect.setTopLeft( event -> pos()); rubberBandRect.setBottomRight( event -> pos()); updateRubberBandRegion(); setCursor(Qt::CrossCursor); } } } void Plotter::mouseMoveEvent(QMouseEvent * event ) { if (rubberBandIsShown) { updateRubberBandRegion(); rubberBandRect.setBottomRight( event -> pos()); updateRubberBandRegion(); } } void Plotter::mouseReleaseEvent(QMouseEvent * event ) { if (( event -> button() == Qt::LeftButton) && rubberBandIsShown) { rubberBandIsShown = false ; updateRubberBandRegion(); unsetCursor(); QRect rect = rubberBandRect.normalized(); if (rect.width() < 4 || rect.height() < 4 ) return ; rect.translate( - Margin, - Margin); PlotSettings prevSettings = zoomStack[curZoom]; PlotSettings settings; double dx = prevSettings.spanX() / (width() - 2 * Margin); double dy = prevSettings.spanY() / (height() - 2 * Margin); settings.minX = prevSettings.minX + dx * rect.left(); settings.maxX = prevSettings.minX + dx * rect.right(); settings.minY = prevSettings.maxY - dy * rect.bottom(); settings.maxY = prevSettings.maxY - dy * rect.top(); settings.adjust(); zoomStack.resize(curZoom + 1 ); zoomStack.append(settings); zoomIn(); } } void Plotter::keyPressEvent(QKeyEvent * event ) { switch ( event -> key()) { case Qt::Key_Plus: zoomIn(); break ; case Qt::Key_Minus: zoomOut(); break ; case Qt::Key_Left: zoomStack[curZoom].scroll( - 1 , 0 ); refreshPixmap(); break ; case Qt::Key_Right: zoomStack[curZoom].scroll( + 1 , 0 ); refreshPixmap(); break ; case Qt::Key_Down: zoomStack[curZoom].scroll( 0 , - 1 ); refreshPixmap(); break ; case Qt::Key_Up: zoomStack[curZoom].scroll( 0 , + 1 ); refreshPixmap(); break ; default : QWidget::keyPressEvent( event ); } } void Plotter::wheelEvent(QWheelEvent * event ) { int numDegrees = event -> delta() / 8 ; int numTicks = numDegrees / 15 ; if ( event -> orientation() == Qt::Horizontal) { zoomStack[curZoom].scroll(numTicks, 0 ); } else { zoomStack[curZoom].scroll( 0 , numTicks); } refreshPixmap(); } void Plotter::updateRubberBandRegion() { QRect rect = rubberBandRect.normalized(); update(rect.left(), rect.top(), rect.width(), 1 ); update(rect.left(), rect.top(), 1 , rect.height()); update(rect.left(), rect.bottom(), rect.width(), 1 ); update(rect.right(), rect.top(), 1 , rect.height()); } void Plotter::refreshPixmap() { pixmap = QPixmap(size()); pixmap.fill( this , 0 , 0 ); QPainter painter( & pixmap); painter.initFrom( this ); drawGrid( & painter); drawCurves( & painter); update(); } void Plotter::drawGrid(QPainter * painter) { QRect rect(Margin, Margin, width() - 2 * Margin, height() - 2 * Margin); if ( ! rect.isValid()) return ; PlotSettings settings = zoomStack[curZoom]; QPen quiteDark = palette().dark().color().light(); QPen light = palette().light().color(); for ( int i = 0 ; i <= settings.numXTicks; ++ i) { int x = rect.left() + (i * (rect.width() - 1 ) / settings.numXTicks); double label = settings.minX + (i * settings.spanX() / settings.numXTicks); painter -> setPen(quiteDark); painter -> drawLine(x, rect.top(), x, rect.bottom()); painter -> setPen(light); painter -> drawLine(x, rect.bottom(), x, rect.bottom() + 5 ); painter -> drawText(x - 50 , rect.bottom() + 5 , 100 , 15 , Qt::AlignHCenter | Qt::AlignTop, QString::number(label)); } for ( int j = 0 ; j <= settings.numYTicks; ++ j) { int y = rect.bottom() - (j * (rect.height() - 1 ) / settings.numYTicks); double label = settings.minY + (j * settings.spanY() / settings.numYTicks); painter -> setPen(quiteDark); painter -> drawLine(rect.left(), y, rect.right(), y); painter -> setPen(light); painter -> drawLine(rect.left() - 5 , y, rect.left(), y); painter -> drawText(rect.left() - Margin, y - 10 , Margin - 5 , 20 , Qt::AlignRight | Qt::AlignVCenter, QString::number(label)); } painter -> drawRect(rect.adjusted( 0 , 0 , - 1 , - 1 )); } void Plotter::drawCurves(QPainter * painter) { static const QColor colorForIds[ 6 ] = { Qt::red, Qt::green, Qt::blue, Qt::cyan, Qt::magenta, Qt::yellow }; PlotSettings settings = zoomStack[curZoom]; QRect rect(Margin, Margin, width() - 2 * Margin, height() - 2 * Margin); if ( ! rect.isValid()) return ; painter -> setClipRect(rect.adjusted( + 1 , + 1 , - 1 , - 1 )); QMapIterator < int , QVector < QPointF > > i(curveMap); while (i.hasNext()) { i.next(); int id = i.key(); const QVector < QPointF > & data = i.value(); QPolygonF polyline(data.count()); for ( int j = 0 ; j < data.count(); ++ j) { double dx = data[j].x() - settings.minX; double dy = data[j].y() - settings.minY; double x = rect.left() + (dx * (rect.width() - 1 ) / settings.spanX()); double y = rect.bottom() - (dy * (rect.height() - 1 ) / settings.spanY()); polyline[j] = QPointF(x, y); } painter -> setPen(colorForIds[ uint (id) % 6 ]); painter -> drawPolyline(polyline); } } PlotSettings::PlotSettings() { minX = 0.0 ; maxX = 10.0 ; numXTicks = 5 ; minY = 0.0 ; maxY = 10.0 ; numYTicks = 5 ; } void PlotSettings::scroll( int dx, int dy) { double stepX = spanX() / numXTicks; minX += dx * stepX; maxX += dx * stepX; double stepY = spanY() / numYTicks; minY += dy * stepY; maxY += dy * stepY; } void PlotSettings::adjust() { adjustAxis(minX, maxX, numXTicks); adjustAxis(minY, maxY, numYTicks); } void PlotSettings::adjustAxis( double & min, double & max, int & numTicks) { const int MinTicks = 4 ; double grossStep = (max - min) / MinTicks; double step = pow( 10.0 , floor(log10(grossStep))); if ( 5 * step < grossStep) { step *= 5 ; } else if ( 2 * step < grossStep) { step *= 2 ; } numTicks = int (ceil(max / step) - floor(min / step)); if (numTicks < MinTicks) numTicks = MinTicks; min = floor(min / step) * step; max = ceil(max / step) * step; } 顶 0 踩 0 上一篇(转) 5.3把自定义控件集成到Qt Designer中(Integrating Custom Widgets with Qt Designer) 下一篇(转)5.4 双缓冲技术(Double Buffering)-2

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