QT在场景中利用freetype实现独立的文字绘制子类QxFreeTypeTextItem，继上一章节讲过qt中如何编译freetype

Qt编译和使用freetype矢量字库方法https://blog.csdn.net/wangningyu/article/details/138927379#QT利用freetype提取字库图片_qt freetype-CSDN博客文章浏览阅读1.2k次。这是某个项目中要用到的片段，结合上一篇文章#QT从字体名获取字库文件路径使用// 保存位图int SaveBitmapToFile(HBITMAP hBitmap, LPSTR lpFileName){HDC hDC;int iBits;WORD wBitCount; DWORD dwPaletteSize=0,dwBmBitsSize,dwDIBSize_qt freetypehttps://blog.csdn.net/wangningyu/article/details/109743104MFC/QT利用COM组件接口从字体名称、粗体、斜体获取到字体文件路径的方法-CSDN博客文章浏览阅读239次。【代码】MFC/QT利用COM组件接口从字体名称、粗体、斜体获取到字体文件路径的方法。https://blog.csdn.net/wangningyu/article/details/138802620

这里将不使用qt默认的QGraphicsSimpleTextItem与QGraphicsTextItem实现一下自定义的文字图形类:

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <QGridLayout>
#include <QPushButton>

#include <QGraphicsScene>
#include <QGraphicsItem>
#include <QDebug>
#include <QPainter>
#include <QFont>
#include <QString>
#include <QColor>
#include <QTextDocument>
#include <ft2build.h>
#include FT_FREETYPE_H

class QxFreeTypeTextItem : public QGraphicsItem
{
public:
    QxFreeTypeTextItem(const QString& text, int fontSize, const QString& ttfFile, const QColor& textColor, QGraphicsItem* parent = nullptr)
        : QGraphicsItem(parent), m_strText(text), m_iFontSize(fontSize), m_strTtfFile(ttfFile), m_textColor(textColor)
    {
        m_ftLibrary = NULL;
        m_ftFace = NULL;

        if (FT_Init_FreeType(&m_ftLibrary))
        {
            qDebug() << "FT_Init_FreeType failed.";
            return;
        }

        if (FT_New_Face(m_ftLibrary, m_strTtfFile.toStdString().c_str(), 0, &m_ftFace))
        {
            qDebug() << "FT_New_Face failed: " << m_strTtfFile;
            return;
        }

        FT_Set_Pixel_Sizes(m_ftFace, 0, m_iFontSize);
    }

    ~QxFreeTypeTextItem()
    {
        if(m_ftFace)
        {
            FT_Done_Face(m_ftFace);
            m_ftFace = NULL;
        }

        if(m_ftLibrary)
        {
            FT_Done_FreeType(m_ftLibrary);
            m_ftLibrary = NULL;
        }
    }

    QRectF boundingRect() const override
    {
        return m_rect;
    }

    void setRect(qreal left, qreal top, qreal width, qreal height)
    {
        m_rect = QRectF(left, top, width, height);
        update();
    }

    void paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget = nullptr) override
    {
        int x = m_rect.left();
        int y = m_rect.top();

        Q_UNUSED(option);
        Q_UNUSED(widget);

        // 开始利用freetype绘制文字
        painter->setRenderHint(QPainter::Antialiasing);
        painter->setPen(m_textColor);
        for (int i = 0; i < m_strText.length(); ++i)
        {
            QChar   ucode = m_strText.at(i);
            ushort  unicode = ucode.unicode();
            if (FT_Load_Char(m_ftFace, unicode, FT_LOAD_RENDER))
            {
                continue;
            }

            FT_GlyphSlot    glyph = m_ftFace->glyph;
            QImage          glyphImage(glyph->bitmap.width, glyph->bitmap.rows, QImage::Format_ARGB32);

            glyphImage.fill(Qt::transparent);
            for (unsigned int j = 0; j < glyph->bitmap.rows; ++j)
            {
                for (unsigned int k = 0; k < glyph->bitmap.width; ++k)
                {
                    int alpha = glyph->bitmap.buffer[j * glyph->bitmap.width + k];
                    glyphImage.setPixel(k, j, qRgba(m_textColor.red(), m_textColor.green(), m_textColor.blue(), alpha));
                }
            }

            painter->drawImage(QPointF(x + glyph->bitmap_left, y - glyph->bitmap_top), glyphImage);
            x += (glyph->advance.x >> 6);
        }
    }

private:
    QString     m_strText;
    int         m_iFontSize;
    QString     m_strTtfFile;
    QColor      m_textColor;
    FT_Library  m_ftLibrary;
    FT_Face     m_ftFace;
    QRectF      m_rect;
};

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);


    QGraphicsScene  *pScene = new QGraphicsScene(this);
    pScene->setSceneRect(QRect(0, 0, 800, 500));
    ui->graphicsView->setScene(pScene);
    ui->graphicsView->setRenderHint(QPainter::Antialiasing);
    //ui->graphicsView->setCacheMode(QGraphicsView::CacheBackground);
    //ui->graphicsView->setViewportUpdateMode(QGraphicsView::BoundingRectViewportUpdate);
    ui->graphicsView->setAlignment(Qt::AlignVCenter | Qt::AlignHCenter);
    ui->graphicsView->setMouseTracking(true);
    ui->graphicsView->setStyleSheet(QString("background:%1").arg(QColor(255, 255, 176).name()));

    QColor              clr(0, 0, 255);
    QxFreeTypeTextItem  *pItem = new QxFreeTypeTextItem("FreeType: Hello-Normal by wangningyu", 32, "C:/ArialUMS.TTF", clr);
    pItem->setRect(10, 10, 300, 100);
    pItem->setFlag(QGraphicsItem::ItemIsMovable, true);
    pItem->setFlag(QGraphicsItem::ItemIsSelectable, true);
    pScene->addItem(pItem);

    pItem = new QxFreeTypeTextItem("FreeType: Hello-Bold by wangningyu", 32, "C:/Windows/Fonts/Arialbd.ttf", clr);
    pItem->setRect(10, 50, 300, 100);
    pItem->setFlag(QGraphicsItem::ItemIsMovable, true);
    pItem->setFlag(QGraphicsItem::ItemIsSelectable, true);
    pScene->addItem(pItem);

    pItem = new QxFreeTypeTextItem("FreeType: Hello-Italic by wangningyu", 32, "C:/Windows/Fonts/Ariali.ttf", clr);
    pItem->setRect(10, 90, 300, 100);
    pItem->setFlag(QGraphicsItem::ItemIsMovable, true);
    pItem->setFlag(QGraphicsItem::ItemIsSelectable, true);
    pScene->addItem(pItem);

    pItem = new QxFreeTypeTextItem("FreeType: Hello-Bold-Italic by wangningyu", 32, "C:/Windows/Fonts/Arialbi.ttf", clr);
    pItem->setRect(10, 130, 300, 100);
    pItem->setFlag(QGraphicsItem::ItemIsMovable, true);
    pItem->setFlag(QGraphicsItem::ItemIsSelectable, true);
    pScene->addItem(pItem);
}

MainWindow::~MainWindow()
{
    delete ui;
}

测试效果：