在不缩放的情况下绘制 QGraphicsItem

Question

我有一个从 QGraphicsRectItem 派生的自定义 class。我所需要的只是在这个项目上画一个框架，并在右下角画一些方块。框架的宽度和块的大小是固定的，但项目可以使用 QGraphicsItem::setTransform 函数进行缩放。问题是，当我尝试将项目的边界矩形映射到视图时，我得到一个不准确的输出矩形，并且该矩形超出了项目的边界。请看下面的代码：

#ifndef TEST_H
#define TEST_H

#include "ui_Test.h"

#include <QGraphicsRectItem>

class MyItem : public QGraphicsRectItem
{
public:
    explicit MyItem(QGraphicsItem *parent = Q_NULLPTR);

    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = Q_NULLPTR) Q_DECL_OVERRIDE;

private:
    void drawVolumeIndicator(QPainter *painter);
};

class Test : public QMainWindow, private Ui::TestClass
{
    Q_OBJECT

public:
    explicit Test(QWidget *parent = Q_NULLPTR);
};

#endif // TEST_H

#include "Test.h"

#include <QGraphicsScene>
#include <QGraphicsView>

MyItem::MyItem(QGraphicsItem *parent)
    : QGraphicsRectItem(parent)
{}

void MyItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    QGraphicsRectItem::paint(painter, option, widget);

    drawVolumeIndicator(painter);
}

void MyItem::drawVolumeIndicator(QPainter *painter)
{
    static const auto blockColor = QColor(QStringLiteral("#0097a7"));
    static const auto frameColor = QColor(QStringLiteral("#660097a7"));

    static Q_CONSTEXPR auto blockSize = QSize(12, 40);
    static Q_CONSTEXPR auto blockMargin = 2;
    static Q_CONSTEXPR auto frameWidth = 4;

    const auto outputRect = painter->transform().mapRect(boundingRect());

    painter->save();
    painter->resetTransform();

    // draw block
    const auto x = outputRect.right() - frameWidth - blockMargin - blockSize.width();
    const auto y = outputRect.bottom() - frameWidth - blockMargin - blockSize.height();
    painter->fillRect(QRect(QPoint(x, y), blockSize), blockColor);

    // draw frame
    painter->setBrush(Qt::transparent);
    painter->setPen(QPen(frameColor, frameWidth, Qt::SolidLine, Qt::FlatCap, Qt::MiterJoin));
    painter->drawRect(outputRect);

    painter->restore();
}

Test::Test(QWidget *parent)
    : QMainWindow(parent)
{
    setupUi(this);

    resize(200, 400);

    auto item = new MyItem;
    item->setBrush(Qt::lightGray);
    item->setPen(QPen(Qt::transparent));
    item->setRect(0, 0, 100, 100);

    // set scale for the item
    QTransform transform;
    transform.scale(1, 3);
    item->setTransform(transform);

    auto scene = new QGraphicsScene;
    scene->addItem(item);

    auto view = new QGraphicsView;
    view->setScene(scene);

    QMainWindow::setCentralWidget(view);
}

这是没有缩放的样子：

这是缩放后的样子：

Answer 1

解决方法是给item设置null pen，画框的时候也调整一下output rect。所以，最后，我的代码如下所示：

#include "Test.h"

#include <QDebug>
#include <QGraphicsScene>
#include <QGraphicsView>

MyItem::MyItem(QGraphicsItem *parent)
    : QGraphicsRectItem(parent)
{}

void MyItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    QGraphicsRectItem::paint(painter, option, widget);

    drawVolumeIndicator(painter);
}

void MyItem::drawVolumeIndicator(QPainter *painter)
{
    static const auto blockColor = QColor(QStringLiteral("#0097a7"));
    static const auto frameColor = QColor(QStringLiteral("#660097a7"));

    static Q_CONSTEXPR auto blockSize = QSize(12, 40);
    static Q_CONSTEXPR auto blockMargin = 2;
    static Q_CONSTEXPR auto frameWidth = 4;
    static Q_CONSTEXPR auto halfFrameWidth = frameWidth / 2;

    const auto outputRect = painter->transform().mapRect(boundingRect());

    painter->save();
    painter->resetTransform();

    // draw block
    const auto x = outputRect.right() - frameWidth - blockMargin - blockSize.width();
    const auto y = outputRect.bottom() - frameWidth - blockMargin - blockSize.height();
    painter->fillRect(QRect(QPoint(x, y), blockSize), blockColor);

    // draw frame
    painter->setBrush(Qt::transparent);
    painter->setPen(QPen(frameColor, frameWidth, Qt::SolidLine, Qt::FlatCap, Qt::MiterJoin));
    painter->drawRect(outputRect.adjusted(halfFrameWidth, halfFrameWidth, -halfFrameWidth, -halfFrameWidth));

    painter->restore();
}

Test::Test(QWidget *parent)
    : QMainWindow(parent)
{
    setupUi(this);

    resize(200, 400);

    auto item = new MyItem;
    item->setBrush(Qt::lightGray);
    item->setPen(Qt::NoPen);
    item->setRect(0, 0, 100, 100);

    // set scale for the item
    QTransform transform;
    transform.scale(1, 3);
    item->setTransform(transform);

    auto scene = new QGraphicsScene;
    scene->addItem(item);

    auto view = new QGraphicsView;
    view->setScene(scene);

    QMainWindow::setCentralWidget(view);
}

在不缩放的情况下绘制 QGraphicsItem

Painting over QGraphicsItem without scaling

qt5

qgraphicsitem