問題描述

我有一個應用程序，屏幕中間有一個 QGraphicsView 窗口.我希望能夠使用鼠標滾輪滾動放大和縮小.

I have an application with a QGraphicsView window in the middle of the screen. I want to be able to zoom in and out using a mouse wheel scroll.

目前我重新實現了 QGraphicsView 并覆蓋了鼠標滾動功能，這樣它就不會滾動圖像(就像默認情況下一樣).

Currently I have re-implemented QGraphicsView and overriden the mouse scroll function so that it doesn't scroll the image (like it does by default).

void MyQGraphicsView::wheelEvent(QWheelEvent *event)
{
    if(event->delta() > 0)
    {
        emit mouseWheelZoom(true);
    }
    else
    {
        emit mouseWheelZoom(false);
    }
}

所以當我滾動時，如果鼠標滾輪向前，我會發出一個信號 true 如果鼠標滾輪返回 false.

so when I scroll, I'm emitting a signal true if mouse wheel forward false if mouse wheel back.

然后我將此信號連接到處理我的 GUI 內容的類中的一個插槽(縮放功能見下文).現在基本上我認為我的縮放功能根本不是最好的方法我已經看到一些人使用覆蓋的wheelevent 函數來設置比例的例子，但我真的找不到完整的答案.

I have then connected this signal to a slot (zoom function see below) in the class that handles my GUI stuff. Now basically I think my zoom function just isn't the best way to do it at all I have seen some examples of people using the overriden wheelevent function to set scales but I couldn't really find a complete answer.

因此，我已經這樣做了，但無論如何它都不是完美的，所以我希望對此進行一些調整，或者尋找在輪子事件函數中使用比例的工作示例.

So instead I have done this but it's not perfect by any means so I'm looking for this to be tweaked a bit or for a working example using scale in the wheel event function.

我在構造函數中將 m_zoom_level 初始化為 0.

I initialize m_zoom_level to 0 in the constructor.

void Display::zoomfunction(bool zoom)
{
    QMatrix matrix;

    if(zoom && m_zoom_level < 500)
    {
        m_zoom_level = m_zoom_level + 10;
        ui->graphicsView->setTransformationAnchor(QGraphicsView::AnchorUnderMouse);
        matrix.scale(m_zoom_level, m_zoom_level);

        ui->graphicsView->setMatrix(matrix);
        ui->graphicsView->scale(1,-1);
    }
    else if(!zoom)
    {
        m_zoom_level = m_zoom_level - 10;
        ui->graphicsView->setTransformationAnchor(QGraphicsView::AnchorUnderMouse);
        matrix.scale(m_zoom_level, m_zoom_level);

        ui->graphicsView->setMatrix(matrix);
        ui->graphicsView->scale(1,-1);
    }
}

正如您在上面看到的，我正在使用 QMatrix 并對其進行縮放并將其設置為 Graphicsview 并將轉換錨點設置為鼠標下方，但有時它無法正常工作，如果我是滾動加載它只會開始放大(我認為這與 int 循環或其他事情有關).

As you can see above I'm using a QMatrix and scaling that and setting it to the Graphicsview and setting the transformation anchor to under mouse, but its just not working perfectly sometimes if I'm scrolling loads it will just start to zoom in only (which I think is to do with the int looping over or something).

正如我所說的，這方面的幫助或鼠標下縮放的好例子會很棒.

As I said help with this or a good example of scale under mouse would be great.

推薦答案

這種縮放有點棘手.讓我分享我自己的課程.

Such zooming is a bit tricky. Let me share my own class for doing that.

標題:

#include <QObject>
#include <QGraphicsView>

/*!
 * This class adds ability to zoom QGraphicsView using mouse wheel. The point under cursor
 * remains motionless while it's possible.
 *
 * Note that it becomes not possible when the scene's
 * size is not large enough comparing to the viewport size. QGraphicsView centers the picture
 * when it's smaller than the view. And QGraphicsView's scrolls boundaries don't allow to
 * put any picture point at any viewport position.
 *
 * When the user starts scrolling, this class remembers original scene position and
 * keeps it until scrolling is completed. It's better than getting original scene position at
 * each scrolling step because that approach leads to position errors due to before-mentioned
 * positioning restrictions.
 *
 * When zommed using scroll, this class emits zoomed() signal.
 *
 * Usage:
 *
 *   new Graphics_view_zoom(view);
 *
 * The object will be deleted automatically when the view is deleted.
 *
 * You can set keyboard modifiers used for zooming using set_modified(). Zooming will be
 * performed only on exact match of modifiers combination. The default modifier is Ctrl.
 *
 * You can change zoom velocity by calling set_zoom_factor_base().
 * Zoom coefficient is calculated as zoom_factor_base^angle_delta
 * (see QWheelEvent::angleDelta).
 * The default zoom factor base is 1.0015.
 */
class Graphics_view_zoom : public QObject {
  Q_OBJECT
public:
  Graphics_view_zoom(QGraphicsView* view);
  void gentle_zoom(double factor);
  void set_modifiers(Qt::KeyboardModifiers modifiers);
  void set_zoom_factor_base(double value);

private:
  QGraphicsView* _view;
  Qt::KeyboardModifiers _modifiers;
  double _zoom_factor_base;
  QPointF target_scene_pos, target_viewport_pos;
  bool eventFilter(QObject* object, QEvent* event);

signals:
  void zoomed();
};

來源:

#include "Graphics_view_zoom.h"
#include <QMouseEvent>
#include <QApplication>
#include <QScrollBar>
#include <qmath.h>

Graphics_view_zoom::Graphics_view_zoom(QGraphicsView* view)
  : QObject(view), _view(view)
{
  _view->viewport()->installEventFilter(this);
  _view->setMouseTracking(true);
  _modifiers = Qt::ControlModifier;
  _zoom_factor_base = 1.0015;
}

void Graphics_view_zoom::gentle_zoom(double factor) {
  _view->scale(factor, factor);
  _view->centerOn(target_scene_pos);
  QPointF delta_viewport_pos = target_viewport_pos - QPointF(_view->viewport()->width() / 2.0,
                                                             _view->viewport()->height() / 2.0);
  QPointF viewport_center = _view->mapFromScene(target_scene_pos) - delta_viewport_pos;
  _view->centerOn(_view->mapToScene(viewport_center.toPoint()));
  emit zoomed();
}

void Graphics_view_zoom::set_modifiers(Qt::KeyboardModifiers modifiers) {
  _modifiers = modifiers;

}

void Graphics_view_zoom::set_zoom_factor_base(double value) {
  _zoom_factor_base = value;
}

bool Graphics_view_zoom::eventFilter(QObject *object, QEvent *event) {
  if (event->type() == QEvent::MouseMove) {
    QMouseEvent* mouse_event = static_cast<QMouseEvent*>(event);
    QPointF delta = target_viewport_pos - mouse_event->pos();
    if (qAbs(delta.x()) > 5 || qAbs(delta.y()) > 5) {
      target_viewport_pos = mouse_event->pos();
      target_scene_pos = _view->mapToScene(mouse_event->pos());
    }
  } else if (event->type() == QEvent::Wheel) {
    QWheelEvent* wheel_event = static_cast<QWheelEvent*>(event);
    if (QApplication::keyboardModifiers() == _modifiers) {
      if (wheel_event->orientation() == Qt::Vertical) {
        double angle = wheel_event->angleDelta().y();
        double factor = qPow(_zoom_factor_base, angle);
        gentle_zoom(factor);
        return true;
      }
    }
  }
  Q_UNUSED(object)
  return false;
}

使用示例:

Graphics_view_zoom* z = new Graphics_view_zoom(ui->graphicsView);
z->set_modifiers(Qt::NoModifier);

這篇關于QGraphicsView 使用鼠標滾輪在鼠標位置下放大和縮小的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！