context2d.h Example File
script/context2d/context2d.h

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 #ifndef CONTEXT2D_H
 #define CONTEXT2D_H

 #include "domimage.h"

 #include <QPainter>
 #include <QPainterPath>
 #include <QString>
 #include <QStack>
 #include <QMetaType>
 #include <QTimerEvent>

 // [3]
 class CanvasGradient
 {
 public:
     CanvasGradient(const QGradient &v)
         : value(v) {}
     CanvasGradient() {}

     QGradient value;
 };
 // [3]

 Q_DECLARE_METATYPE(CanvasGradient)
 Q_DECLARE_METATYPE(CanvasGradient*)

 class ImageData {
 };

 class QContext2DCanvas;

 class Context2D : public QObject
 {
     Q_OBJECT
     // compositing
     Q_PROPERTY(qreal globalAlpha READ globalAlpha WRITE setGlobalAlpha)
     Q_PROPERTY(QString globalCompositeOperation READ globalCompositeOperation WRITE setGlobalCompositeOperation)
     Q_PROPERTY(QVariant strokeStyle READ strokeStyle WRITE setStrokeStyle)
     Q_PROPERTY(QVariant fillStyle READ fillStyle WRITE setFillStyle)
     // line caps/joins
     Q_PROPERTY(qreal lineWidth READ lineWidth WRITE setLineWidth)
     Q_PROPERTY(QString lineCap READ lineCap WRITE setLineCap)
     Q_PROPERTY(QString lineJoin READ lineJoin WRITE setLineJoin)
     Q_PROPERTY(qreal miterLimit READ miterLimit WRITE setMiterLimit)
     // shadows
     Q_PROPERTY(qreal shadowOffsetX READ shadowOffsetX WRITE setShadowOffsetX)
     Q_PROPERTY(qreal shadowOffsetY READ shadowOffsetY WRITE setShadowOffsetY)
     Q_PROPERTY(qreal shadowBlur READ shadowBlur WRITE setShadowBlur)
     Q_PROPERTY(QString shadowColor READ shadowColor WRITE setShadowColor)

 public:
     Context2D(QObject *parent = 0);
     void setSize(int width, int height);
     void setSize(const QSize &size);
     QSize size() const;

     void clear();
     void reset();

     // compositing
     qreal globalAlpha() const; // (default 1.0)
     QString globalCompositeOperation() const; // (default over)
     QVariant strokeStyle() const; // (default black)
     QVariant fillStyle() const; // (default black)

     void setGlobalAlpha(qreal alpha);
     void setGlobalCompositeOperation(const QString &op);
     void setStrokeStyle(const QVariant &style);
     void setFillStyle(const QVariant &style);

     // line caps/joins
     qreal lineWidth() const; // (default 1)
     QString lineCap() const; // "butt", "round", "square" (default "butt")
     QString lineJoin() const; // "round", "bevel", "miter" (default "miter")
     qreal miterLimit() const; // (default 10)

     void setLineWidth(qreal w);
     void setLineCap(const QString &s);
     void setLineJoin(const QString &s);
     void setMiterLimit(qreal m);

     // shadows
     qreal shadowOffsetX() const; // (default 0)
     qreal shadowOffsetY() const; // (default 0)
     qreal shadowBlur() const; // (default 0)
     QString shadowColor() const; // (default black)

     void setShadowOffsetX(qreal x);
     void setShadowOffsetY(qreal y);
     void setShadowBlur(qreal b);
     void setShadowColor(const QString &str);

 public slots:
     void save(); // push state on state stack
     void restore(); // pop state stack and restore state

     void scale(qreal x, qreal y);
     void rotate(qreal angle);
     void translate(qreal x, qreal y);
     void transform(qreal m11, qreal m12, qreal m21, qreal m22,
                    qreal dx, qreal dy);
     void setTransform(qreal m11, qreal m12, qreal m21, qreal m22,
                       qreal dx, qreal dy);

     CanvasGradient createLinearGradient(qreal x0, qreal y0,
                                         qreal x1, qreal y1);
     CanvasGradient createRadialGradient(qreal x0, qreal y0,
                                         qreal r0, qreal x1,
                                         qreal y1, qreal r1);

     // rects
     void clearRect(qreal x, qreal y, qreal w, qreal h);
     void fillRect(qreal x, qreal y, qreal w, qreal h);
     void strokeRect(qreal x, qreal y, qreal w, qreal h);

     // path API
     void beginPath();
     void closePath();
     void moveTo(qreal x, qreal y);
     void lineTo(qreal x, qreal y);
     void quadraticCurveTo(qreal cpx, qreal cpy, qreal x, qreal y);
     void bezierCurveTo(qreal cp1x, qreal cp1y,
                        qreal cp2x, qreal cp2y, qreal x, qreal y);
     void arcTo(qreal x1, qreal y1, qreal x2, qreal y2, qreal radius);
     void rect(qreal x, qreal y, qreal w, qreal h);
     void arc(qreal x, qreal y, qreal radius,
              qreal startAngle, qreal endAngle,
              bool anticlockwise);
     void fill();
     void stroke();
     void clip();
     bool isPointInPath(qreal x, qreal y) const;

     // drawing images
     void drawImage(DomImage *image, qreal dx, qreal dy);
     void drawImage(DomImage *image, qreal dx, qreal dy,
                    qreal dw, qreal dh);
     void drawImage(DomImage *image, qreal sx, qreal sy,
                    qreal sw, qreal sh, qreal dx, qreal dy,
                    qreal dw, qreal dh);

     // pixel manipulation
     ImageData getImageData(qreal sx, qreal sy, qreal sw, qreal sh);
     void putImageData(ImageData image, qreal dx, qreal dy);

 signals:
     void changed(const QImage &image);

 protected:
     void timerEvent(QTimerEvent *e);

 private:
     void beginPainting();
     const QImage &endPainting();
     void scheduleChange();

     int m_changeTimerId;
     QImage  m_image;
     QPainter m_painter;
     QPainterPath m_path;

     enum DirtyFlag {
         DirtyTransformationMatrix = 0x00001,
         DirtyClippingRegion       = 0x00002,
         DirtyStrokeStyle          = 0x00004,
         DirtyFillStyle            = 0x00008,
         DirtyGlobalAlpha          = 0x00010,
         DirtyLineWidth            = 0x00020,
         DirtyLineCap              = 0x00040,
         DirtyLineJoin             = 0x00080,
         DirtyMiterLimit           = 0x00100,
         MDirtyPen                 = DirtyStrokeStyle
                                   | DirtyLineWidth
                                   | DirtyLineCap
                                   | DirtyLineJoin
                                   | DirtyMiterLimit,
         DirtyShadowOffsetX        = 0x00200,
         DirtyShadowOffsetY        = 0x00400,
         DirtyShadowBlur           = 0x00800,
         DirtyShadowColor          = 0x01000,
         DirtyGlobalCompositeOperation = 0x2000,
         DirtyFont                 = 0x04000,
         DirtyTextAlign            = 0x08000,
         DirtyTextBaseline         = 0x10000,
         AllIsFullOfDirt           = 0xfffff
     };

     struct State {
         State() : flags(0) {}
         QMatrix matrix;
         QPainterPath clipPath;
         QBrush strokeStyle;
         QBrush fillStyle;
         qreal globalAlpha;
         qreal lineWidth;
         Qt::PenCapStyle lineCap;
         Qt::PenJoinStyle lineJoin;
         qreal miterLimit;
         qreal shadowOffsetX;
         qreal shadowOffsetY;
         qreal shadowBlur;
         QColor shadowColor;
         QPainter::CompositionMode globalCompositeOperation;
         QFont font;
         int textAlign;
         int textBaseline;
         int flags;
     };
     State m_state;
     QStack<State> m_stateStack;
 };

 #endif