New algorithm for drawing thin lines

Added a new QCosmeticStroker class for drawing thin
lines. The class can handle both aliased and antialiased
lines.

The code replaces all the midpoint line drawing algorithms in
the raster paintengine and gives correct subpixel positioning
for lines.

It gives around 30% to 50% speedup against the midpoint algorithm. If
we missed that fast path, the speedup is around between a factor of
6 to 8 for lines and aliased paths and 100 and 400 for antialiased
paths.

Reviewed-by: Kim

1 files changed, 101 insertions, 0 deletions

diff --git a/src/gui/painting/qcosmeticstroker_p.h b/src/gui/painting/qcosmeticstroker_p.h
new file mode 100644
index 0000000..bc6dd76
--- /dev/null
+++ b/src/gui/painting/qcosmeticstroker_p.h
@@ -0,0 +1,101 @@
+#ifndef QCOSMETICSTROKER_P_H
+#define QCOSMETICSTROKER_P_H
+
+#include <private/qdrawhelper_p.h>
+#include <private/qvectorpath_p.h>
+#include <private/qpaintengine_raster_p.h>
+#include <qpen.h>
+
+class QCosmeticStroker;
+
+
+typedef void (*StrokeLine)(QCosmeticStroker *stroker, qreal x1, qreal y1, qreal x2, qreal y2, int caps);
+
+class QCosmeticStroker
+{
+public:
+    struct Point {
+        int x;
+        int y;
+    };
+    struct PointF {
+        qreal x;
+        qreal y;
+    };
+
+    enum Caps {
+        NoCaps = 0,
+        CapBegin = 0x1,
+        CapEnd = 0x2,
+    };
+
+    // used to avoid drop outs or duplicated points
+    enum Direction {
+        TopToBottom,
+        BottomToTop,
+        LeftToRight,
+        RightToLeft
+    };
+
+    QCosmeticStroker(QRasterPaintEngineState *s, const QRect &dr)
+        : state(s),
+          clip(dr),
+          pattern(0),
+          reversePattern(0),
+          patternSize(0),
+          patternLength(0),
+          patternOffset(0),
+          current_span(0),
+          lastDir(LeftToRight),
+          lastAxisAligned(false)
+    { setup(); }
+    ~QCosmeticStroker() { free(pattern); free(reversePattern); }
+    void drawLine(const QPointF &p1, const QPointF &p2);
+    void drawPath(const QVectorPath &path);
+    void drawPoints(const QPoint *points, int num);
+    void drawPoints(const QPointF *points, int num);
+
+
+    QRasterPaintEngineState *state;
+    QRect clip;
+    // clip bounds in real
+    qreal xmin, xmax;
+    qreal ymin, ymax;
+
+    StrokeLine stroke;
+    bool drawCaps;
+
+    int *pattern;
+    int *reversePattern;
+    int patternSize;
+    int patternLength;
+    int patternOffset;
+
+    enum { NSPANS = 255 };
+    QT_FT_Span spans[NSPANS];
+    int current_span;
+    ProcessSpans blend;
+
+    int opacity;
+
+    uint color;
+    uint *pixels;
+    int ppl;
+
+    Direction lastDir;
+    Point lastPixel;
+    bool lastAxisAligned;
+
+private:
+    void setup();
+
+    void renderCubic(const QPointF &p1, const QPointF &p2, const QPointF &p3, const QPointF &p4, int caps);
+    void renderCubicSubdivision(PointF *points, int level, int caps);
+    // used for closed subpaths
+    void calculateLastPoint(qreal rx1, qreal ry1, qreal rx2, qreal ry2);
+
+public:
+    bool clipLine(qreal &x1, qreal &y1, qreal &x2, qreal &y2);
+};
+
+#endif // QCOSMETICLINE_H