QGraphicsView::fitInView 是选择显示范围并将视图居中的必需函数。
以下是如何使用它的完整示例。
// https://github.com/KubaO/stackoverflown/tree/master/questions/scene-radar-40680065
#include <QtWidgets>
#include <random>
首先，让我们获取随机目标位置。场景按照例如海里的比例缩放：因此，场景中的任何坐标都应该是这些单位。这只是一种约定：场景本身并不关心，视图也不关心。参考点位于0,0：所有范围/方位角度数都相对于原点。
QPointF randomPosition() {
static std::random_device dev;
static std::default_random_engine eng(dev());
static std::uniform_real_distribution<double> posDis(-100., 100.);
return {posDis(eng), posDis(eng)};
}
然后，为了帮助打开和关闭场景组件（例如格网），需要为它们创建一个空的父组件：
class EmptyItem : public QGraphicsItem {
public:
QRectF boundingRect() const override { return QRectF(); }
void paint(QPainter *, const QStyleOptionGraphicsItem *, QWidget *) override {}
};
一个场景管理器设置显示。空项目充当项目集合，可以轻松地隐藏/显示而无需修改子项目。它们还强制执行其子项的相对 Z 顺序。
class SceneManager : public QObject {
Q_OBJECT
Q_PROPERTY(bool microGraticuleVisible READ microGraticuleVisible WRITE setMicroGraticuleVisible)
QGraphicsScene m_scene;
QPen m_targetPen{Qt::green, 1};
EmptyItem m_target, m_center, m_macroGraticule, m_microGraticule;
可以在视图上安装事件过滤器以在视图调整大小时发出信号。这可用于使视图保持居中，尽管调整大小：
bool eventFilter(QObject *watched, QEvent *event) override {
if (event->type() == QEvent::Resize
&& qobject_cast<QGraphicsView*>(watched))
emit viewResized();
return QObject::eventFilter(watched, event);
}
场景的Z顺序如下：中心十字、宏观和微观网格，然后是位于顶部的目标。
public:
SceneManager() {
m_scene.addItem(&m_center);
m_scene.addItem(&m_macroGraticule);
m_scene.addItem(&m_microGraticule);
m_scene.addItem(&m_target);
m_targetPen.setCosmetic(true);
addGraticules();
}
我们可以监视图形视图的大小调整；我们还公开微网格的可见性。
void monitor(QGraphicsView *view) { view->installEventFilter(this); }
QGraphicsScene * scene() { return &m_scene; }
Q_SLOT void setMicroGraticuleVisible(bool vis) { m_microGraticule.setVisible(vis); }
bool microGraticuleVisible() const { return m_microGraticule.isVisible(); }
Q_SIGNAL void viewResized();
目标可以随机生成，目标在视图坐标中具有固定大小。但它的位置可能会受到任何从场景到视图的转换的影响。
目标和栅格线的笔是装饰性笔：它们的宽度以视图设备单位（像素）而不是场景单位来表示。
void newTargets(int count = 200) {
qDeleteAll(m_target.childItems());
for (int i = 0; i < count; ++i) {
auto target = new QGraphicsEllipseItem(-1.5, -1.5, 3., 3., &m_target);
target->setPos(randomPosition());
target->setPen(m_targetPen);
target->setBrush(m_targetPen.color());
target->setFlags(QGraphicsItem::ItemIgnoresTransformations);
}
}
格网线是以原点（范围参考点）为圆心的同心圆和一个十字架。原点的十字架在视图单位中具有固定的大小 - 这由
ItemIgnoresTransformations标志指示。
void addGraticules() {
QPen pen{Qt::white, 1};
pen.setCosmetic(true);
auto center = {QLineF{-5.,0.,5.,0.}, QLineF{0.,-5.,0.,5.}};
for (auto l : center) {
auto c = new QGraphicsLineItem{l, &m_center};
c->setFlags(QGraphicsItem::ItemIgnoresTransformations);
c->setPen(pen);
}
for (auto range = 10.; range < 101.; range += 10.) {
auto circle = new QGraphicsEllipseItem(0.-range, 0.-range, 2.*range, 2.*range, &m_macroGraticule);
circle->setPen(pen);
}
pen = QPen{Qt::white, 1, Qt::DashLine};
pen.setCosmetic(true);
for (auto range = 2.5; range < 9.9; range += 2.5) {
auto circle = new QGraphicsEllipseItem(0.-range, 0.-range, 2.*range, 2.*range, &m_microGraticule);
circle->setPen(pen);
}
}
};
场景单元与视图之间的映射关系如下所示：
Each time the view range is changed (from e.g. the combo box), the QGraphicsView::fitInView method is called with a rectangle in scene units (of nautical miles). This takes care of all of the scaling, centering, etc.. E.g. to select a range of 10NM, we'd call view.fitInView(QRect{-10.,-10.,20.,20.), Qt::KeepAspectRatio)
The graticule(s) can be disabled/enabled as appropriate for a given range to unclutter the view.
int main(int argc, char ** argv) {
QApplication app{argc, argv};
SceneManager mgr;
mgr.newTargets();
QWidget w;
QGridLayout layout{&w};
QGraphicsView view;
QComboBox combo;
QPushButton newTargets{"New Targets"};
layout.addWidget(&view, 0, 0, 1, 2);
layout.addWidget(&combo, 1, 0);
layout.addWidget(&newTargets, 1, 1);
view.setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
view.setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
view.setBackgroundBrush(Qt::black);
view.setScene(mgr.scene());
view.setRenderHint(QPainter::Antialiasing);
mgr.monitor(&view);
combo.addItems({"10", "25", "50", "100"});
auto const recenterView = [&]{
auto range = combo.currentText().toDouble();
view.fitInView(-range, -range, 2.*range, 2.*range, Qt::KeepAspectRatio);
mgr.setMicroGraticuleVisible(range <= 20.);
};
QObject::connect(&combo, &QComboBox::currentTextChanged, recenterView);
QObject::connect(&mgr, &SceneManager::viewResized, recenterView);
QObject::connect(&newTargets, &QPushButton::clicked, [&]{ mgr.newTargets(); });
w.show();
return app.exec();
}
#include "main.moc"
QPoint（range * cos（bearing），range * sin（bearing）的坐标处。缩放选择场景和视图之间的映射，以便给定数量的英里适合视图中。场景会照顾其余的事情。 - Kuba hasn't forgotten Monica