Zoom issue QGraphicsView - c++

Question

I am trying to zoom in with a scale between 1 and 10 in a QGraphicsView. The code I have is complex but I created a minimal reproducible example as follows:
main.cpp
#include <QApplication>
#include "mainwindow.h"
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
MainWindow mainWin;
mainWin.show();
return app.exec();
}
CustomGraphicsView.h
#include
class CustomGraphicsView : public QGraphicsView
{
public:
CustomGraphicsView(QGraphicsScene* scene, QWidget* parent = nullptr) : QGraphicsView(scene, parent) {}
void resizeEvent(QResizeEvent* event) override;
inline void setSceneSize(int origX, int origY, int sizeX, int sizeY) {
m_SceneOrigX = origX;
m_SceneOrigY = origY;
m_SceneSizeX = sizeX;
m_SceneSizeY = sizeY;
}
void resize();
private:
int m_SceneOrigX = -1;
int m_SceneOrigY = -1;
int m_SceneSizeX = -1;
int m_SceneSizeY = -1;
};
CustomGraphicsView.cpp
#include "customgraphicsview.h"
void CustomGraphicsView::resizeEvent(QResizeEvent* event)
{
fitInView(m_SceneOrigX, m_SceneOrigY, m_SceneSizeX, m_SceneSizeY, Qt::KeepAspectRatio);
QGraphicsView::resizeEvent(event);
}
void CustomGraphicsView::resize()
{
fitInView(m_SceneOrigX, m_SceneOrigY, m_SceneSizeX, m_SceneSizeY, Qt::KeepAspectRatio);
}
MainWindow.h
#include <QMainWindow>
#include "customgraphicsview.h"
#include <QSlider>
#include <QGraphicsScene>
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow();
private slots:
void showItems();
void setZoomLevel(int zoom);
private:
QGraphicsScene* m_Scene;
CustomGraphicsView* m_View;
QWidget* m_MainView;
QSlider* m_ZoomSlider;
double m_CurrentZoomLevel = 1.0;
};
MainWindow.cpp
#include "mainwindow.h"
#include <QVBoxLayout>
#include <QGraphicsRectItem>
MainWindow::MainWindow()
{
setMinimumHeight(600);
setMinimumWidth(800);
m_Scene = new QGraphicsScene();
m_View = new CustomGraphicsView(m_Scene);
m_View->setAttribute(Qt::WA_AlwaysShowToolTips);
m_MainView = new QWidget();
m_ZoomSlider = new QSlider(Qt::Horizontal);
m_ZoomSlider->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Preferred);
m_ZoomSlider->setTickPosition(QSlider::TicksAbove);
m_ZoomSlider->setMinimum(1);
m_ZoomSlider->setMaximum(10);
m_ZoomSlider->setTickInterval(1);
QVBoxLayout* vLayout = new QVBoxLayout();
vLayout->addWidget(m_View);
vLayout->addWidget(m_ZoomSlider);
m_MainView->setLayout(vLayout);
setCentralWidget(m_MainView);
connect(m_ZoomSlider, &QSlider::valueChanged, this, &MainWindow::setZoomLevel);
showItems();
}
void MainWindow::showItems() {
m_Scene->clear();
m_View->resetTransform();
m_Scene->setSceneRect(QRectF());
m_View->setSceneRect(QRectF());
m_View->fitInView(QRectF());
for (int i = 0; i < 9; i++) {
int row = i % 3;
int col = i / 3;
QGraphicsRectItem* squareItem = new QGraphicsRectItem(0, 0, 3000 * 1000, 3000 * 1000);
m_Scene->addItem(squareItem);
squareItem->setPen(QPen(QBrush(Qt::black), 10000));
squareItem->setPos((col - 1) * 3000 * 1000, (row - 1) * 3000 * 1000);
}
m_Scene->setSceneRect(-3000 * 1000, -3000 * 1000, 4 * 3000 * 1000, 4 * 3000 * 1000);
m_View->setSceneSize(-3000 * 1000 / m_CurrentZoomLevel, -3000 * 1000 / m_CurrentZoomLevel, 4 * 3000 * 1000 / m_CurrentZoomLevel, 4 * 3000 * 1000 / m_CurrentZoomLevel);
}
void MainWindow::setZoomLevel(int zoom) {
m_CurrentZoomLevel = zoom;
showItems();
}
CMakeLists.txt
cmake_minimum_required (VERSION 3.10)
project (ZoomTestProject CXX)
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTOUIC ON)
set(CMAKE_INCLUDE_CURRENT_DIR ON)
set(CMAKE_AUTORCC ON)
set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS 1)
find_package(Qt6 COMPONENTS Core Widgets)
cmake_policy(SET CMP0020 NEW)
cmake_policy(SET CMP0043 NEW)
include_directories(
${Qt6Widgets_INCLUDE_DIRS}
${Qt6Core_INCLUDE_DIRS})
set(DOCK_SRCS
main.cpp
mainwindow.cpp
customgraphicsview.cpp
)
set(DOCK_HEADR
mainwindow.h
customgraphicsview.h
)
add_executable(ZoomTestProject
${DOCK_SRCS}
${DOCK_HEADR})
target_link_libraries(ZoomTestProject
Qt6::Widgets
Qt6::Core)
set(ROOT_PATH ${Qt6_DIR}/../../../)
install(TARGETS ZoomTestProject DESTINATION bin)
install(FILES ${ROOT_PATH}/bin/Qt6Core.dll DESTINATION bin)
install(FILES ${ROOT_PATH}/bin/Qt6Gui.dll DESTINATION bin)
install(FILES ${ROOT_PATH}/bin/Qt6Widgets.dll DESTINATION bin)
install(FILES ${ROOT_PATH}/plugins/platforms/qwindows.dll DESTINATION bin/platforms)
The problem that I have is that when I zooming in , when I move the slider the first time to a zoom level, it zooms correctly (scroll bars are correctly positioned, the size of the shown elements is correct). When I move the slider again it zooms to a very big level, the scroll bars are not correct anymore. If I move the slider further nothing happens anymore, the extreme zoom level remains, the scroll bars keep their false size.
Does anyone have an idea about what this can be ?

Answer 1

I have solved this as follows:
Do not call fitinView inside the resize event of the customgraphicsview
Implement a function called resize in the customgraphicsview as follows:
void CustomGraphicsView::resize()
{
fitInView(m_SceneOrigX, m_SceneOrigY, m_SceneSizeX, m_SceneSizeY, Qt::KeepAspectRatio);
}
In the showItems() function of mainwindow do at the end as follows:
m_Scene->setSceneRect(-3000 * 1000, -3000 * 1000, 4 * 3000 * 1000, 4 * 3000 * 1000);
m_View->scale(m_ScaleFactor, m_ScaleFactor);
m_View->setSceneSize(-3000 * 1000 / m_CurrentZoomLevel, -3000 * 1000 / m_CurrentZoomLevel, 4 * 3000 * 1000 / m_CurrentZoomLevel, 4 * 3000 * 1000 / m_CurrentZoomLevel);
m_View->resize();
The setZoomLevel() function in the mainwindow was changed as follows:
void MainWindow::setZoomLevel(int zoom) {
m_ScaleFactor = double(zoom) / m_CurrentZoomLevel;
m_CurrentZoomLevel = zoom;
showItems();
}
The essence of the problem is that fitInView call when resizing of customgraphicsview does not work with the zoom function. I have read in other threads that a solution to this would be to always show the scrollbars in the view. I tried this as well but did not bring any results.
I hope this helps someone in need.