qcosmeticstroker.cpp

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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
#include "qcosmeticstroker_p.h"
#include "private/qpainterpath_p.h"
#include "private/qrgba64_p.h"
#include <qdebug.h>
 
QT_BEGIN_NAMESPACE
 
#if 0
inline QString capString(int caps)
{
    QString str;
    if (caps & QCosmeticStroker::CapBegin) {
        str += "CapBegin ";
    }
    if (caps & QCosmeticStroker::CapEnd) {
        str += "CapEnd ";
    }
    return str;
}
#endif
 
#if Q_PROCESSOR_WORDSIZE == 8
typedef qint64 FDot16;
#else
typedef int FDot16;
#endif
 
#define toF26Dot6(x) static_cast<int>((x) * 64.)
 
static inline uint sourceOver(uint d, uint color)
{
    return color + BYTE_MUL(d, qAlpha(~color));
}
 
inline static FDot16 FDot16FixedDiv(int x, int y)
{
#if Q_PROCESSOR_WORDSIZE == 8
    return FDot16(x) * (1<<16) / y;
#else
    if (qAbs(x) > 0x7fff)
        return static_cast<qlonglong>(x) * (1<<16) / y;
    return x * (1<<16) / y;
#endif
}
 
typedef void (*DrawPixel)(QCosmeticStroker *stroker, int x, int y, int coverage);
 
namespace {
 
struct Dasher {
    QCosmeticStroker *stroker;
    int *pattern;
    int offset;
    int dashIndex;
    int dashOn;
 
    Dasher(QCosmeticStroker *s, bool reverse, int start, int stop)
        : stroker(s)
    {
        int delta = stop - start;
        if (reverse) {
            pattern = stroker->reversePattern;
            offset = stroker->patternLength - stroker->patternOffset - delta - ((start & 63) - 32);
            dashOn = 0;
        } else {
            pattern = stroker->pattern;
            offset = stroker->patternOffset - ((start & 63) - 32);
            dashOn = 1;
        }
        offset %= stroker->patternLength;
        if (offset < 0)
            offset += stroker->patternLength;
 
        dashIndex = 0;
        while (dashIndex < stroker->patternSize - 1 && offset>= pattern[dashIndex])
            ++dashIndex;
 
//        qDebug() << "   dasher" << offset/64. << reverse << dashIndex;
        stroker->patternOffset += delta;
        stroker->patternOffset %= stroker->patternLength;
    }
 
    bool on() const {
        return (dashIndex + dashOn) & 1;
    }
    void adjust() {
        offset += 64;
        if (offset >= pattern[dashIndex]) {
            ++dashIndex;
            dashIndex %= stroker->patternSize;
        }
        offset %= stroker->patternLength;
//        qDebug() << "dasher.adjust" << offset/64. << dashIndex;
    }
};
 
struct NoDasher {
    NoDasher(QCosmeticStroker *, bool, int, int) {}
    bool on() const { return true; }
    void adjust(int = 0) {}
};
 
};
 
/*
 * The return value is the result of the clipLine() call performed at the start
 * of each of the two functions, aka "false" means completely outside the devices
 * rect.
 */
template<DrawPixel drawPixel, class Dasher>
static bool drawLine(QCosmeticStroker *stroker, qreal x1, qreal y1, qreal x2, qreal y2, int caps);
template<DrawPixel drawPixel, class Dasher>
static bool drawLineAA(QCosmeticStroker *stroker, qreal x1, qreal y1, qreal x2, qreal y2, int caps);
 
inline void drawPixel(QCosmeticStroker *stroker, int x, int y, int coverage)
{
    const QRect &cl = stroker->clip;
    if (x < cl.x() || x > cl.right() || y < cl.y() || y > cl.bottom())
        return;
 
    if (stroker->current_span > 0) {
        const int lastx = stroker->spans[stroker->current_span-1].x + stroker->spans[stroker->current_span-1].len ;
        const int lasty = stroker->spans[stroker->current_span-1].y;
 
        if (stroker->current_span == QCosmeticStroker::NSPANS || y < lasty || (y == lasty && x < lastx)) {
            stroker->blend(stroker->current_span, stroker->spans, &stroker->state->penData);
            stroker->current_span = 0;
        }
    }
 
    stroker->spans[stroker->current_span].x = x;
    stroker->spans[stroker->current_span].len = 1;
    stroker->spans[stroker->current_span].y = y;
    stroker->spans[stroker->current_span].coverage = coverage*stroker->opacity >> 8;
    ++stroker->current_span;
}
 
inline void drawPixelARGB32(QCosmeticStroker *stroker, int x, int y, int coverage)
{
    const QRect &cl = stroker->clip;
    if (x < cl.x() || x > cl.right() || y < cl.y() || y > cl.bottom())
        return;
 
    int offset = x + stroker->ppl*y;
    uint c = BYTE_MUL(stroker->color, coverage);
    stroker->pixels[offset] = sourceOver(stroker->pixels[offset], c);
}
 
inline void drawPixelARGB32Opaque(QCosmeticStroker *stroker, int x, int y, int)
{
    const QRect &cl = stroker->clip;
    if (x < cl.x() || x > cl.right() || y < cl.y() || y > cl.bottom())
        return;
 
    int offset = x + stroker->ppl*y;
    stroker->pixels[offset] = sourceOver(stroker->pixels[offset], stroker->color);
}
 
enum StrokeSelection {
    Aliased = 0,
    AntiAliased = 1,
    Solid = 0,
    Dashed = 2,
    RegularDraw = 0,
    FastDraw = 4
};
 
static StrokeLine strokeLine(int strokeSelection)
{
    StrokeLine stroke;
 
    switch (strokeSelection) {
    case Aliased|Solid|RegularDraw:
        stroke = &QT_PREPEND_NAMESPACE(drawLine)<drawPixel, NoDasher>;
        break;
    case Aliased|Solid|FastDraw:
        stroke = &QT_PREPEND_NAMESPACE(drawLine)<drawPixelARGB32Opaque, NoDasher>;
        break;
    case Aliased|Dashed|RegularDraw:
        stroke = &QT_PREPEND_NAMESPACE(drawLine)<drawPixel, Dasher>;
        break;
    case Aliased|Dashed|FastDraw:
        stroke = &QT_PREPEND_NAMESPACE(drawLine)<drawPixelARGB32Opaque, Dasher>;
        break;
    case AntiAliased|Solid|RegularDraw:
        stroke = &QT_PREPEND_NAMESPACE(drawLineAA)<drawPixel, NoDasher>;
        break;
    case AntiAliased|Solid|FastDraw:
        stroke = &QT_PREPEND_NAMESPACE(drawLineAA)<drawPixelARGB32, NoDasher>;
        break;
    case AntiAliased|Dashed|RegularDraw:
        stroke = &QT_PREPEND_NAMESPACE(drawLineAA)<drawPixel, Dasher>;
        break;
    case AntiAliased|Dashed|FastDraw:
        stroke = &QT_PREPEND_NAMESPACE(drawLineAA)<drawPixelARGB32, Dasher>;
        break;
    default:
        Q_ASSERT(false);
        stroke = nullptr;
    }
    return stroke;
}
 
void QCosmeticStroker::setup()
{
    blend = state->penData.blend;
    if (state->clip && state->clip->enabled && state->clip->hasRectClip && !state->clip->clipRect.isEmpty()) {
        clip &= state->clip->clipRect;
        blend = state->penData.unclipped_blend;
    }
 
    int strokeSelection = 0;
    if (blend == state->penData.unclipped_blend
        && state->penData.type == QSpanData::Solid
        && (state->penData.rasterBuffer->format == QImage::Format_ARGB32_Premultiplied
            || state->penData.rasterBuffer->format == QImage::Format_RGB32)
        && state->compositionMode() == QPainter::CompositionMode_SourceOver)
        strokeSelection |= FastDraw;
 
    if (state->renderHints & QPainter::Antialiasing)
        strokeSelection |= AntiAliased;
 
    const QList<qreal> &penPattern = state->lastPen.dashPattern();
    if (penPattern.isEmpty() || penPattern.size() > 1024) {
        Q_ASSERT(!pattern && !reversePattern);
        pattern = nullptr;
        reversePattern = nullptr;
        patternLength = 0;
        patternSize = 0;
    } else {
        pattern = static_cast<int *>(malloc(penPattern.size() * sizeof(int)));
        reversePattern = static_cast<int *>(malloc(penPattern.size() * sizeof(int)));
        patternSize = penPattern.size();
 
        patternLength = 0;
        for (int i = 0; i < patternSize; ++i) {
            patternLength += static_cast<int>(qBound(1., penPattern.at(i) * 64, 65536.));
            pattern[i] = patternLength;
        }
        patternLength = 0;
        for (int i = 0; i < patternSize; ++i) {
            patternLength += static_cast<int>(qBound(1., penPattern.at(patternSize - 1 - i) * 64, 65536.));
            reversePattern[i] = patternLength;
        }
        strokeSelection |= Dashed;
//        qDebug() << "setup: size=" << patternSize << "length=" << patternLength/64.;
    }
 
    stroke = strokeLine(strokeSelection);
 
    qreal width = state->lastPen.widthF();
    if (width == 0)
        opacity = 256;
    else if (state->lastPen.isCosmetic())
        opacity = static_cast<int>(256 * width);
    else
        opacity = static_cast<int>(256 * width * state->txscale);
    opacity = qBound(0, opacity, 256);
 
    drawCaps = state->lastPen.capStyle() != Qt::FlatCap;
 
    if (strokeSelection & FastDraw) {
        color = multiplyAlpha256(state->penData.solidColor.rgba64(), opacity).toArgb32();
        QRasterBuffer *buffer = state->penData.rasterBuffer;
        pixels = reinterpret_cast<uint *>(buffer->buffer());
        ppl = buffer->stride<quint32>();
    }
 
    // line drawing produces different results with different clips, so
    // we need to clip consistently when painting to the same device
 
    // setup FP clip bounds
    xmin = deviceRect.left() - 1;
    xmax = deviceRect.right() + 2;
    ymin = deviceRect.top() - 1;
    ymax = deviceRect.bottom() + 2;
 
    lastPixel.x = INT_MIN;
    lastPixel.y = INT_MIN;
}
 
// returns true if the whole line gets clipped away
bool QCosmeticStroker::clipLine(qreal &x1, qreal &y1, qreal &x2, qreal &y2)
{
    if (!qIsFinite(x1) || !qIsFinite(y1) || !qIsFinite(x2) || !qIsFinite(y2))
        return true;
    // basic/rough clipping is done in floating point coordinates to avoid
    // integer overflow problems.
    if (x1 < xmin) {
        if (x2 <= xmin)
            goto clipped;
        y1 += (y2 - y1)/(x2 - x1) * (xmin - x1);
        x1 = xmin;
    } else if (x1 > xmax) {
        if (x2 >= xmax)
            goto clipped;
        y1 += (y2 - y1)/(x2 - x1) * (xmax - x1);
        x1 = xmax;
    }
    if (x2 < xmin) {
        lastPixel.x = INT_MIN;
        y2 += (y2 - y1)/(x2 - x1) * (xmin - x2);
        x2 = xmin;
    } else if (x2 > xmax) {
        lastPixel.x = INT_MIN;
        y2 += (y2 - y1)/(x2 - x1) * (xmax - x2);
        x2 = xmax;
    }
 
    if (y1 < ymin) {
        if (y2 <= ymin)
            goto clipped;
        x1 += (x2 - x1)/(y2 - y1) * (ymin - y1);
        y1 = ymin;
    } else if (y1 > ymax) {
        if (y2 >= ymax)
            goto clipped;
        x1 += (x2 - x1)/(y2 - y1) * (ymax - y1);
        y1 = ymax;
    }
    if (y2 < ymin) {
        lastPixel.x = INT_MIN;
        x2 += (x2 - x1)/(y2 - y1) * (ymin - y2);
        y2 = ymin;
    } else if (y2 > ymax) {
        lastPixel.x = INT_MIN;
        x2 += (x2 - x1)/(y2 - y1) * (ymax - y2);
        y2 = ymax;
    }
 
    return false;
 
  clipped:
    lastPixel.x = INT_MIN;
    return true;
}
 
 
void QCosmeticStroker::drawLine(const QPointF &p1, const QPointF &p2)
{
    QPointF start = p1 * state->matrix;
    QPointF end = p2 * state->matrix;
 
    if (start == end) {
        drawPoints(&p1, 1);
        return;
    }
 
    patternOffset = state->lastPen.dashOffset()*64;
    lastPixel.x = INT_MIN;
    lastPixel.y = INT_MIN;
 
    stroke(this, start.x(), start.y(), end.x(), end.y(), drawCaps ? CapBegin|CapEnd : 0);
 
    blend(current_span, spans, &state->penData);
    current_span = 0;
}
 
void QCosmeticStroker::drawPoints(const QPoint *points, int num)
{
    const QPoint *end = points + num;
    while (points < end) {
        QPointF p = QPointF(*points) * state->matrix;
        drawPixel(this, std::floor(p.x()), std::floor(p.y()), 255);
        ++points;
    }
 
    blend(current_span, spans, &state->penData);
    current_span = 0;
}
 
void QCosmeticStroker::drawPoints(const QPointF *points, int num)
{
    const QPointF *end = points + num;
    while (points < end) {
        QPointF p = (*points) * state->matrix;
        drawPixel(this, std::floor(p.x()), std::floor(p.y()), 255);
        ++points;
    }
 
    blend(current_span, spans, &state->penData);
    current_span = 0;
}
 
void QCosmeticStroker::calculateLastPoint(qreal rx1, qreal ry1, qreal rx2, qreal ry2)
{
    // this is basically the same code as used in the aliased stroke method,
    // but it only determines the direction and last point of a line
    //
    // This is being used to have proper dropout control for closed contours
    // by calculating the direction and last pixel of the last segment in the contour.
    // the info is then used to perform dropout control when drawing the first line segment
    // of the contour
    lastPixel.x = INT_MIN;
    lastPixel.y = INT_MIN;
 
    if (clipLine(rx1, ry1, rx2, ry2))
        return;
 
    int x1 = toF26Dot6(rx1);
    int y1 = toF26Dot6(ry1);
    int x2 = toF26Dot6(rx2);
    int y2 = toF26Dot6(ry2);
 
    int dx = qAbs(x2 - x1);
    int dy = qAbs(y2 - y1);
 
    if (dx < dy) {
        // vertical
        bool swapped = false;
        if (y1 > y2) {
            swapped = true;
            qSwap(y1, y2);
            qSwap(x1, x2);
        }
        FDot16 xinc = FDot16FixedDiv(x2 - x1, y2 - y1);
        FDot16 x = FDot16(x1) * (1<<10);
 
        int y = (y1 + 32) >> 6;
        int ys = (y2 + 32) >> 6;
 
        int round = (xinc > 0) ? 32 : 0;
        if (y != ys) {
            x += ((y * (1<<6)) + round - y1) * xinc >> 6;
 
            if (swapped) {
                lastPixel.x = x >> 16;
                lastPixel.y = y;
                lastDir = QCosmeticStroker::BottomToTop;
            } else {
                lastPixel.x = (x + (ys - y - 1)*xinc) >> 16;
                lastPixel.y = ys - 1;
                lastDir = QCosmeticStroker::TopToBottom;
            }
            lastAxisAligned = qAbs(xinc) < (1 << 14);
        }
    } else {
        // horizontal
        if (!dx)
            return;
 
        bool swapped = false;
        if (x1 > x2) {
            swapped = true;
            qSwap(x1, x2);
            qSwap(y1, y2);
        }
        FDot16 yinc = FDot16FixedDiv(y2 - y1, x2 - x1);
        FDot16 y = FDot16(y1) * (1 << 10);
 
        int x = (x1 + 32) >> 6;
        int xs = (x2 + 32) >> 6;
 
        int round = (yinc > 0) ? 32 : 0;
        if (x != xs) {
            y += ((x * (1<<6)) + round - x1) * yinc >> 6;
 
            if (swapped) {
                lastPixel.x = x;
                lastPixel.y = y >> 16;
                lastDir = QCosmeticStroker::RightToLeft;
            } else {
                lastPixel.x = xs - 1;
                lastPixel.y = (y + (xs - x - 1)*yinc) >> 16;
                lastDir = QCosmeticStroker::LeftToRight;
            }
            lastAxisAligned = qAbs(yinc) < (1 << 14);
        }
    }
//    qDebug() << "   moveTo: setting last pixel to x/y dir" << lastPixel.x << lastPixel.y << lastDir;
}
 
static inline const QPainterPath::ElementType *subPath(const QPainterPath::ElementType *t, const QPainterPath::ElementType *end,
                                                 const qreal *points, bool *closed)
{
    const QPainterPath::ElementType *start = t;
    ++t;
 
    // find out if the subpath is closed
    while (t < end) {
        if (*t == QPainterPath::MoveToElement)
            break;
        ++t;
    }
 
    int offset = t - start - 1;
//    qDebug() << "subpath" << offset << points[0] << points[1] << points[2*offset] << points[2*offset+1];
    *closed = (points[0] == points[2*offset] && points[1] == points[2*offset + 1]);
 
    return t;
}
 
void QCosmeticStroker::drawPath(const QVectorPath &path)
{
//    qDebug() << ">>>> drawpath" << path.convertToPainterPath()
//             << "antialiasing:" << (bool)(state->renderHints & QPainter::Antialiasing) << " implicit close:" << path.hasImplicitClose();
    if (path.isEmpty())
        return;
 
    const qreal *points = path.points();
    const QPainterPath::ElementType *type = path.elements();
 
    if (type) {
        const QPainterPath::ElementType *end = type + path.elementCount();
 
        while (type < end) {
            Q_ASSERT(type == path.elements() || *type == QPainterPath::MoveToElement);
 
            QPointF p = QPointF(points[0], points[1]) * state->matrix;
            patternOffset = state->lastPen.dashOffset()*64;
            lastPixel.x = INT_MIN;
            lastPixel.y = INT_MIN;
 
            bool closed;
            const QPainterPath::ElementType *e = subPath(type, end, points, &closed);
            if (closed) {
                const qreal *p = points + 2*(e-type);
                QPointF p1 = QPointF(p[-4], p[-3]) * state->matrix;
                QPointF p2 = QPointF(p[-2], p[-1]) * state->matrix;
                calculateLastPoint(p1.x(), p1.y(), p2.x(), p2.y());
            }
            int caps = (!closed && drawCaps) ? CapBegin : NoCaps;
//            qDebug() << "closed =" << closed << capString(caps);
 
            points += 2;
            ++type;
 
            while (type < e) {
                QPointF p2 = QPointF(points[0], points[1]) * state->matrix;
                switch (*type) {
                case QPainterPath::MoveToElement:
                    Q_ASSERT(!"Logic error");
                    break;
 
                case QPainterPath::LineToElement:
                    if (!closed && drawCaps && type == e - 1)
                        caps |= CapEnd;
                    stroke(this, p.x(), p.y(), p2.x(), p2.y(), caps);
                    p = p2;
                    points += 2;
                    ++type;
                    break;
 
                case QPainterPath::CurveToElement: {
                    if (!closed && drawCaps && type == e - 3)
                        caps |= CapEnd;
                    QPointF p3 = QPointF(points[2], points[3]) * state->matrix;
                    QPointF p4 = QPointF(points[4], points[5]) * state->matrix;
                    renderCubic(p, p2, p3, p4, caps);
                    p = p4;
                    type += 3;
                    points += 6;
                    break;
                }
                case QPainterPath::CurveToDataElement:
                    Q_ASSERT(!"QPainterPath::toSubpathPolygons(), bad element type");
                    break;
                }
                caps = NoCaps;
            }
        }
    } else { // !type, simple polygon
        QPointF p = QPointF(points[0], points[1]) * state->matrix;
        QPointF movedTo = p;
        patternOffset = state->lastPen.dashOffset()*64;
        lastPixel.x = INT_MIN;
        lastPixel.y = INT_MIN;
 
        const qreal *begin = points;
        const qreal *end = points + 2*path.elementCount();
        // handle closed path case
        bool closed = path.hasImplicitClose() || (points[0] == end[-2] && points[1] == end[-1]);
        int caps = (!closed && drawCaps) ? CapBegin : NoCaps;
        if (closed) {
            QPointF p2;
            if (points[0] == end[-2] && points[1] == end[-1] && path.elementCount() > 2)
                p2 = QPointF(end[-4], end[-3]) * state->matrix;
            else
                p2 = QPointF(end[-2], end[-1]) * state->matrix;
            calculateLastPoint(p2.x(), p2.y(), p.x(), p.y());
        }
 
        bool fastPenAliased = (state->flags.fast_pen && !state->flags.antialiased);
        points += 2;
        while (points < end) {
            QPointF p2 = QPointF(points[0], points[1]) * state->matrix;
 
            if (!closed && drawCaps && points == end - 2)
                caps |= CapEnd;
 
            bool moveNextStart = stroke(this, p.x(), p.y(), p2.x(), p2.y(), caps);
 
            /* fix for gaps in polylines with fastpen and aliased in a sequence
               of points with small distances: if current point p2 has been dropped
               out, keep last non dropped point p.
 
               However, if the line was completely outside the devicerect, we
               still need to update p to avoid drawing the line after this one from
               a bad starting position.
            */
            if (!fastPenAliased || moveNextStart || points == begin + 2 || points == end - 2)
                p = p2;
            points += 2;
            caps = NoCaps;
        }
        if (path.hasImplicitClose())
            stroke(this, p.x(), p.y(), movedTo.x(), movedTo.y(), NoCaps);
    }
 
 
    blend(current_span, spans, &state->penData);
    current_span = 0;
}
 
void QCosmeticStroker::renderCubic(const QPointF &p1, const QPointF &p2, const QPointF &p3, const QPointF &p4, int caps)
{
//    qDebug() << ">>>> renderCubic" << p1 << p2 << p3 << p4 << capString(caps);
    const int maxSubDivisions = 6;
    PointF points[3*maxSubDivisions + 4];
 
    points[3].x = p1.x();
    points[3].y = p1.y();
    points[2].x = p2.x();
    points[2].y = p2.y();
    points[1].x = p3.x();
    points[1].y = p3.y();
    points[0].x = p4.x();
    points[0].y = p4.y();
 
    PointF *p = points;
    int level = maxSubDivisions;
 
    renderCubicSubdivision(p, level, caps);
}
 
static void splitCubic(QCosmeticStroker::PointF *points)
{
    const qreal half = .5;
    qreal  a, b, c, d;
 
    points[6].x = points[3].x;
    c = points[1].x;
    d = points[2].x;
    points[1].x = a = ( points[0].x + c ) * half;
    points[5].x = b = ( points[3].x + d ) * half;
    c = ( c + d ) * half;
    points[2].x = a = ( a + c ) * half;
    points[4].x = b = ( b + c ) * half;
    points[3].x = ( a + b ) * half;
 
    points[6].y = points[3].y;
    c = points[1].y;
    d = points[2].y;
    points[1].y = a = ( points[0].y + c ) * half;
    points[5].y = b = ( points[3].y + d ) * half;
    c = ( c + d ) * half;
    points[2].y = a = ( a + c ) * half;
    points[4].y = b = ( b + c ) * half;
    points[3].y = ( a + b ) * half;
}
 
void QCosmeticStroker::renderCubicSubdivision(QCosmeticStroker::PointF *points, int level, int caps)
{
    if (level) {
        qreal dx = points[3].x - points[0].x;
        qreal dy = points[3].y - points[0].y;
        qreal len = static_cast<qreal>(.25) * (qAbs(dx) + qAbs(dy));
 
        if (qAbs(dx * (points[0].y - points[2].y) - dy * (points[0].x - points[2].x)) >= len ||
            qAbs(dx * (points[0].y - points[1].y) - dy * (points[0].x - points[1].x)) >= len) {
            splitCubic(points);
 
            --level;
            renderCubicSubdivision(points + 3, level, caps & CapBegin);
            renderCubicSubdivision(points, level, caps & CapEnd);
            return;
        }
    }
 
    stroke(this, points[3].x, points[3].y, points[0].x, points[0].y, caps);
}
 
static inline int swapCaps(int caps)
{
    return ((caps & QCosmeticStroker::CapBegin) << 1) |
           ((caps & QCosmeticStroker::CapEnd) >> 1);
}
 
// adjust line by half a pixel
static inline void capAdjust(int caps, int &x1, int &x2, FDot16 &y, FDot16 yinc)
{
    if (caps & QCosmeticStroker::CapBegin) {
        x1 -= 32;
        y -= yinc >> 1;
    }
    if (caps & QCosmeticStroker::CapEnd) {
        x2 += 32;
    }
}
 
/*
  The hard part about this is dropout control and avoiding douple drawing of points when
  the drawing shifts from horizontal to vertical or back.
  */
template<DrawPixel drawPixel, class Dasher>
static bool drawLine(QCosmeticStroker *stroker, qreal rx1, qreal ry1, qreal rx2, qreal ry2, int caps)
{
    bool didDraw = qAbs(rx2 - rx1) + qAbs(ry2 - ry1) >= 1.0;
 
    if (stroker->clipLine(rx1, ry1, rx2, ry2))
        return true;
 
    int x1 = toF26Dot6(rx1);
    int y1 = toF26Dot6(ry1);
    int x2 = toF26Dot6(rx2);
    int y2 = toF26Dot6(ry2);
 
    int dx = qAbs(x2 - x1);
    int dy = qAbs(y2 - y1);
 
    QCosmeticStroker::Point last = stroker->lastPixel;
 
//    qDebug() << "stroke" << x1/64. << y1/64. << x2/64. << y2/64.;
 
    if (dx < dy) {
        // vertical
        QCosmeticStroker::Direction dir = QCosmeticStroker::TopToBottom;
 
        bool swapped = false;
        if (y1 > y2) {
            swapped = true;
            qSwap(y1, y2);
            qSwap(x1, x2);
            caps = swapCaps(caps);
            dir = QCosmeticStroker::BottomToTop;
        }
        FDot16 xinc = FDot16FixedDiv(x2 - x1, y2 - y1);
        FDot16 x = FDot16(x1) * (1<<10);
 
        if ((stroker->lastDir ^ QCosmeticStroker::VerticalMask) == dir)
            caps |= swapped ? QCosmeticStroker::CapEnd : QCosmeticStroker::CapBegin;
 
        capAdjust(caps, y1, y2, x, xinc);
 
        int y = (y1 + 32) >> 6;
        int ys = (y2 + 32) >> 6;
        int round = (xinc > 0) ? 32 : 0;
 
        // If capAdjust made us round away from what calculateLastPoint gave us,
        // round back the other way so we start and end on the right point.
        if ((caps & QCosmeticStroker::CapBegin) && stroker->lastPixel.y == y + 1)
           y++;
 
        if (y != ys) {
            x += ((y * (1<<6)) + round - y1) * xinc >> 6;
 
            // calculate first and last pixel and perform dropout control
            QCosmeticStroker::Point first;
            first.x = x >> 16;
            first.y = y;
            last.x = (x + (ys - y - 1)*xinc) >> 16;
            last.y = ys - 1;
            if (swapped)
                qSwap(first, last);
 
            bool axisAligned = qAbs(xinc) < (1 << 14);
            if (stroker->lastPixel.x > INT_MIN) {
                if (first.x == stroker->lastPixel.x &&
                    first.y == stroker->lastPixel.y) {
                    // remove duplicated pixel
                    if (swapped) {
                        --ys;
                    } else {
                        ++y;
                        x += xinc;
                    }
                } else if (stroker->lastDir != dir &&
                           (((axisAligned && stroker->lastAxisAligned) &&
                             stroker->lastPixel.x != first.x && stroker->lastPixel.y != first.y) ||
                            (qAbs(stroker->lastPixel.x - first.x) > 1 ||
                             qAbs(stroker->lastPixel.y - first.y) > 1))) {
                    // have a missing pixel, insert it
                    if (swapped) {
                        ++ys;
                    } else {
                        --y;
                        x -= xinc;
                    }
                } else if (stroker->lastDir == dir &&
                           ((qAbs(stroker->lastPixel.x - first.x) <= 1 &&
                             qAbs(stroker->lastPixel.y - first.y) > 1))) {
                    x += xinc >> 1;
                    if (swapped)
                        last.x = (x >> 16);
                    else
                        last.x = (x + (ys - y - 1)*xinc) >> 16;
                }
            }
            stroker->lastDir = dir;
            stroker->lastAxisAligned = axisAligned;
 
            Dasher dasher(stroker, swapped, y * (1<<6), ys * (1<<6));
 
            do {
                if (dasher.on())
                    drawPixel(stroker, x >> 16, y, 255);
                dasher.adjust();
                x += xinc;
            } while (++y < ys);
            didDraw = true;
        }
    } else {
        // horizontal
        if (!dx)
            return true;
 
        QCosmeticStroker::Direction dir = QCosmeticStroker::LeftToRight;
 
        bool swapped = false;
        if (x1 > x2) {
            swapped = true;
            qSwap(x1, x2);
            qSwap(y1, y2);
            caps = swapCaps(caps);
            dir = QCosmeticStroker::RightToLeft;
        }
        FDot16 yinc = FDot16FixedDiv(y2 - y1, x2 - x1);
        FDot16 y = FDot16(y1) * (1<<10);
 
        if ((stroker->lastDir ^ QCosmeticStroker::HorizontalMask) == dir)
            caps |= swapped ? QCosmeticStroker::CapEnd : QCosmeticStroker::CapBegin;
 
        capAdjust(caps, x1, x2, y, yinc);
 
        int x = (x1 + 32) >> 6;
        int xs = (x2 + 32) >> 6;
        int round = (yinc > 0) ? 32 : 0;
 
        // If capAdjust made us round away from what calculateLastPoint gave us,
        // round back the other way so we start and end on the right point.
        if ((caps & QCosmeticStroker::CapBegin) && stroker->lastPixel.x == x + 1)
            x++;
 
        if (x != xs) {
            y += ((x * (1<<6)) + round - x1) * yinc >> 6;
 
            // calculate first and last pixel to perform dropout control
            QCosmeticStroker::Point first;
            first.x = x;
            first.y = y >> 16;
            last.x = xs - 1;
            last.y = (y + (xs - x - 1)*yinc) >> 16;
            if (swapped)
                qSwap(first, last);
 
            bool axisAligned = qAbs(yinc) < (1 << 14);
            if (stroker->lastPixel.x > INT_MIN) {
                if (first.x == stroker->lastPixel.x && first.y == stroker->lastPixel.y) {
                    // remove duplicated pixel
                    if (swapped) {
                        --xs;
                    } else {
                        ++x;
                        y += yinc;
                    }
                } else if (stroker->lastDir != dir &&
                           (((axisAligned && stroker->lastAxisAligned) &&
                             stroker->lastPixel.x != first.x && stroker->lastPixel.y != first.y) ||
                            (qAbs(stroker->lastPixel.x - first.x) > 1 ||
                             qAbs(stroker->lastPixel.y - first.y) > 1))) {
                    // have a missing pixel, insert it
                    if (swapped) {
                        ++xs;
                    } else {
                        --x;
                        y -= yinc;
                    }
                } else if (stroker->lastDir == dir &&
                           ((qAbs(stroker->lastPixel.x - first.x) <= 1 &&
                             qAbs(stroker->lastPixel.y - first.y) > 1))) {
                    y += yinc >> 1;
                    if (swapped)
                        last.y = (y >> 16);
                    else
                        last.y = (y + (xs - x - 1)*yinc) >> 16;
                }
            }
            stroker->lastDir = dir;
            stroker->lastAxisAligned = axisAligned;
 
            Dasher dasher(stroker, swapped, x * (1<<6), xs * (1<<6));
 
            do {
                if (dasher.on())
                    drawPixel(stroker, x, y >> 16, 255);
                dasher.adjust();
                y += yinc;
            } while (++x < xs);
            didDraw = true;
        }
    }
    stroker->lastPixel = last;
    return didDraw;
}
 
 
template<DrawPixel drawPixel, class Dasher>
static bool drawLineAA(QCosmeticStroker *stroker, qreal rx1, qreal ry1, qreal rx2, qreal ry2, int caps)
{
    if (stroker->clipLine(rx1, ry1, rx2, ry2))
        return true;
 
    int x1 = toF26Dot6(rx1);
    int y1 = toF26Dot6(ry1);
    int x2 = toF26Dot6(rx2);
    int y2 = toF26Dot6(ry2);
 
    int dx = x2 - x1;
    int dy = y2 - y1;
 
    if (qAbs(dx) < qAbs(dy)) {
        // vertical
 
        FDot16 xinc = FDot16FixedDiv(dx, dy);
 
        bool swapped = false;
        if (y1 > y2) {
            qSwap(y1, y2);
            qSwap(x1, x2);
            swapped = true;
            caps = swapCaps(caps);
        }
 
        FDot16 x = FDot16(x1 - 32) * (1<<10);
        x -= ( ((y1 & 63) - 32)  * xinc ) >> 6;
 
        capAdjust(caps, y1, y2, x, xinc);
 
        Dasher dasher(stroker, swapped, y1, y2);
 
        int y = y1 >> 6;
        int ys = y2 >> 6;
 
        int alphaStart, alphaEnd;
        if (y == ys) {
            alphaStart = y2 - y1;
            Q_ASSERT(alphaStart >= 0 && alphaStart < 64);
            alphaEnd = 0;
        } else {
            alphaStart = 64 - (y1 & 63);
            alphaEnd = (y2 & 63);
        }
//        qDebug() << "vertical" << x1/64. << y1/64. << x2/64. << y2/64.;
//        qDebug() << "          x=" << x << "dx=" << dx << "xi=" << (x>>16) << "xsi=" << ((x+(ys-y)*dx)>>16) << "y=" << y << "ys=" << ys;
 
        // draw first pixel
        if (dasher.on()) {
            uint alpha = static_cast<quint8>(x >> 8);
            drawPixel(stroker, x>>16, y, (255-alpha) * alphaStart >> 6);
            drawPixel(stroker, (x>>16) + 1, y, alpha * alphaStart >> 6);
        }
        dasher.adjust();
        x += xinc;
        ++y;
        if (y < ys) {
            do {
                if (dasher.on()) {
                    uint alpha = static_cast<quint8>(x >> 8);
                    drawPixel(stroker, x>>16, y, (255-alpha));
                    drawPixel(stroker, (x>>16) + 1, y, alpha);
                }
                dasher.adjust();
                x += xinc;
            } while (++y < ys);
        }
        // draw last pixel
        if (alphaEnd && dasher.on()) {
            uint alpha = static_cast<quint8>(x >> 8);
            drawPixel(stroker, x>>16, y, (255-alpha) * alphaEnd >> 6);
            drawPixel(stroker, (x>>16) + 1, y, alpha * alphaEnd >> 6);
        }
    } else {
        // horizontal
        if (!dx)
            return true;
 
        FDot16 yinc = FDot16FixedDiv(dy, dx);
 
        bool swapped = false;
        if (x1 > x2) {
            qSwap(x1, x2);
            qSwap(y1, y2);
            swapped = true;
            caps = swapCaps(caps);
        }
 
        FDot16 y = FDot16(y1 - 32) * (1<<10);
        y -= ( ((x1 & 63) - 32)  * yinc ) >> 6;
 
        capAdjust(caps, x1, x2, y, yinc);
 
        Dasher dasher(stroker, swapped, x1, x2);
 
        int x = x1 >> 6;
        int xs = x2 >> 6;
 
//        qDebug() << "horizontal" << x1/64. << y1/64. << x2/64. << y2/64.;
//        qDebug() << "          y=" << y << "dy=" << dy << "x=" << x << "xs=" << xs << "yi=" << (y>>16) << "ysi=" << ((y+(xs-x)*dy)>>16);
        int alphaStart, alphaEnd;
        if (x == xs) {
            alphaStart = x2 - x1;
            Q_ASSERT(alphaStart >= 0 && alphaStart < 64);
            alphaEnd = 0;
        } else {
            alphaStart = 64 - (x1 & 63);
            alphaEnd = (x2 & 63);
        }
 
        // draw first pixel
        if (dasher.on()) {
            uint alpha = static_cast<quint8>(y >> 8);
            drawPixel(stroker, x, y>>16, (255-alpha) * alphaStart >> 6);
            drawPixel(stroker, x, (y>>16) + 1, alpha * alphaStart >> 6);
        }
        dasher.adjust();
        y += yinc;
        ++x;
        // draw line
        if (x < xs) {
            do {
                if (dasher.on()) {
                    uint alpha = static_cast<quint8>(y >> 8);
                    drawPixel(stroker, x, y>>16, (255-alpha));
                    drawPixel(stroker, x, (y>>16) + 1, alpha);
                }
                dasher.adjust();
                y += yinc;
            } while (++x < xs);
        }
        // draw last pixel
        if (alphaEnd && dasher.on()) {
            uint alpha = static_cast<quint8>(y >> 8);
            drawPixel(stroker, x, y>>16, (255-alpha) * alphaEnd >> 6);
            drawPixel(stroker, x, (y>>16) + 1, alpha * alphaEnd >> 6);
        }
    }
    return true;
}
 
QT_END_NAMESPACE