Qt源码分析--QPaintEngine

定义：

QPaintEngine 类提供了 QPainter 如何在给定平台上绘制给定设备的抽象定义。

如果想使用 QPainter 绘制到不同的后端(backend)，则必须继承 QPaintEngine 并重新实现其所有虚函数。然后通过继承 QPaintDevice 并重新实现虚函数 QPaintDevice::paintEngine() 来实现 QPaintEngine。

class Q_GUI_EXPORT QPaintEngine
{Q_DECLARE_PRIVATE(QPaintEngine)
public:enum PaintEngineFeature {PrimitiveTransform          = 0x00000001, // Can transform primitives brushesPatternTransform            = 0x00000002, // Can transform pattern brushesPixmapTransform             = 0x00000004, // Can transform pixmapsPatternBrush                = 0x00000008, // Can fill with pixmaps and standard patternsLinearGradientFill          = 0x00000010, // Can fill gradient areasRadialGradientFill          = 0x00000020, // Can render radial gradientsConicalGradientFill         = 0x00000040, // Can render conical gradientsAlphaBlend                  = 0x00000080, // Can do source over alpha blendPorterDuff                  = 0x00000100, // Can do general porter duff compositionsPainterPaths                = 0x00000200, // Can fill, outline and clip pathsAntialiasing                = 0x00000400, // Can antialias linesBrushStroke                 = 0x00000800, // Can render brush based pensConstantOpacity             = 0x00001000, // Can render at constant opacityMaskedBrush                 = 0x00002000, // Can fill with textures that has an alpha channel or maskPerspectiveTransform        = 0x00004000, // Can do perspective transformationsBlendModes                  = 0x00008000, // Can do extended Porter&Duff compositionObjectBoundingModeGradients = 0x00010000, // Can do object bounding mode gradientsRasterOpModes               = 0x00020000, // Can do logical raster operationsPaintOutsidePaintEvent      = 0x20000000, // Engine is capable of painting outside paint events/*                          0x10000000, // Used for emulatingQGradient::StretchToDevice,defined in qpainter.cpp0x40000000, // Used internally for emulating opaque backgrounds*/AllFeatures               = 0xffffffff  // For convenience};Q_DECLARE_FLAGS(PaintEngineFeatures, PaintEngineFeature)enum DirtyFlag {DirtyPen                = 0x0001,DirtyBrush              = 0x0002,DirtyBrushOrigin        = 0x0004,DirtyFont               = 0x0008,DirtyBackground         = 0x0010,DirtyBackgroundMode     = 0x0020,DirtyTransform          = 0x0040,DirtyClipRegion         = 0x0080,DirtyClipPath           = 0x0100,DirtyHints              = 0x0200,DirtyCompositionMode    = 0x0400,DirtyClipEnabled        = 0x0800,DirtyOpacity            = 0x1000,AllDirty                = 0xffff};Q_DECLARE_FLAGS(DirtyFlags, DirtyFlag)enum PolygonDrawMode {OddEvenMode,WindingMode,ConvexMode,PolylineMode};explicit QPaintEngine(PaintEngineFeatures features=PaintEngineFeatures());virtual ~QPaintEngine();bool isActive() const { return active; }void setActive(bool newState) { active = newState; }virtual bool begin(QPaintDevice *pdev) = 0;virtual bool end() = 0;virtual void updateState(const QPaintEngineState &state) = 0;virtual void drawRects(const QRect *rects, int rectCount);virtual void drawRects(const QRectF *rects, int rectCount);virtual void drawLines(const QLine *lines, int lineCount);virtual void drawLines(const QLineF *lines, int lineCount);virtual void drawEllipse(const QRectF &r);virtual void drawEllipse(const QRect &r);virtual void drawPath(const QPainterPath &path);virtual void drawPoints(const QPointF *points, int pointCount);virtual void drawPoints(const QPoint *points, int pointCount);virtual void drawPolygon(const QPointF *points, int pointCount, PolygonDrawMode mode);virtual void drawPolygon(const QPoint *points, int pointCount, PolygonDrawMode mode);virtual void drawPixmap(const QRectF &r, const QPixmap &pm, const QRectF &sr) = 0;virtual void drawTextItem(const QPointF &p, const QTextItem &textItem);virtual void drawTiledPixmap(const QRectF &r, const QPixmap &pixmap, const QPointF &s);virtual void drawImage(const QRectF &r, const QImage &pm, const QRectF &sr,Qt::ImageConversionFlags flags = Qt::AutoColor);void setPaintDevice(QPaintDevice *device);QPaintDevice *paintDevice() const;void setSystemClip(const QRegion &baseClip);QRegion systemClip() const;void setSystemRect(const QRect &rect);QRect systemRect() const;virtual QPoint coordinateOffset() const;enum Type {X11,Windows,QuickDraw, CoreGraphics, MacPrinter,QWindowSystem,PostScript,   // ### Qt 6: Remove, update documentationOpenGL,Picture,SVG,Raster,Direct3D,Pdf,OpenVG,OpenGL2,PaintBuffer,Blitter,Direct2D,User = 50,    // first user type idMaxUser = 100 // last user type id};virtual Type type() const = 0;inline void fix_neg_rect(int *x, int *y, int *w, int *h);inline bool testDirty(DirtyFlags df);inline void setDirty(DirtyFlags df);inline void clearDirty(DirtyFlags df);bool hasFeature(PaintEngineFeatures feature) const { return gccaps & feature; }QPainter *painter() const;void syncState();inline bool isExtended() const { return extended; }
protected:QPaintEngine(QPaintEnginePrivate &data, PaintEngineFeatures devcaps=PaintEngineFeatures());QPaintEngineState *state;PaintEngineFeatures gccaps;uint active : 1;uint selfDestruct : 1;uint extended : 1;QScopedPointer<QPaintEnginePrivate> d_ptr;
private:void setAutoDestruct(bool autoDestr) { selfDestruct = autoDestr; }bool autoDestruct() const { return selfDestruct; }Q_DISABLE_COPY(QPaintEngine)friend class QPainterReplayer;friend class QFontEngineBox;friend class QFontEngineMac;friend class QFontEngineWin;friend class QMacPrintEngine;friend class QMacPrintEnginePrivate;friend class QFontEngineQPF2;friend class QPainter;friend class QPainterPrivate;friend class QWidget;friend class QWidgetPrivate;friend class QWin32PaintEngine;friend class QWin32PaintEnginePrivate;friend class QMacCGContext;friend class QPreviewPaintEngine;friend class QX11GLPlatformPixmap;
};

下次，解析一下QPainter

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