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Use QPainterPath to draw polygons. This method is more straight-forward,
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everything is drawn by one command and doesn't leave artifacts when
painting to Postscript or PDF. Fixes ticket #422.


git-svn-id: http://svn.osgeo.org/qgis/trunk@6193 c8812cc2-4d05-0410-92ff-de0c093fc19c
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wonder committed Dec 5, 2006
1 parent 26f3b8c commit d520791
Showing 1 changed file with 22 additions and 57 deletions.
79 changes: 22 additions & 57 deletions src/gui/qgsvectorlayer.cpp
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Expand Up @@ -45,6 +45,7 @@
#include <QLibrary>
#include <QMessageBox>
#include <QPainter>
#include <QPainterPath>
#include <QPixmap>
#include <QPolygonF>
#include <QProgressDialog>
Expand Down Expand Up @@ -639,26 +640,18 @@ std::cerr << i << ": " << ring->first[i]

// Now we draw the polygons

// use painter paths for drawing polygons with holes
// when adding polygon to the path they invert the area
// this means that adding inner rings to the path creates
// holes in outer ring
QPainterPath path; // OddEven fill rule by default

// Only try to draw polygons if there is something to draw
if (total_points > 0)
{
int ii = 0;
QPointF outerRingPt;

// Stores the start index of each ring (first) and the number
// of points in each ring (second).
typedef std::vector<std::pair<unsigned int, unsigned int> > ringDetailType;
ringDetailType ringDetails;

// Need to copy the polygon vertices into a QPologynF for the
// QPainter::drawpolygon() call. The size is the sum of points in
// the polygon plus one extra point for each ring except for the
// first ring.

// Store size here and use it in the loop to avoid penalty of
// multiple calls to size()
int numRings = rings.size();
QPolygonF pa(total_points + numRings - 1);
for (register int i = 0; i < numRings; ++i)
{
// Store the pointer in a variable with a short name so as to make
Expand All @@ -667,37 +660,15 @@ std::cerr << i << ": " << ring->first[i]
// only do this once to avoid penalty of additional calls
unsigned ringSize = r->first.size();

// Store the start index of this ring, and the number of
// points in the ring.
ringDetails.push_back(std::make_pair(ii, ringSize));

// Transfer points to the array of QPointF
//for (register unsigned int j = 0; j != ringSize; ++j, ++ii)
for (register unsigned int j = 0; j != ringSize; ++j, ii++)
QPolygonF pa(ringSize);
for (register unsigned int j = 0; j != ringSize; ++j)
{
// there is maybe a bug in Qt4.1: when using doubles without rounding,
// I've experienced crashes (broken pipe) when drawing polygon
// with more than 3000 vertices [MD]
//pa[ii].setX(static_cast<int>(r->first[j] + 0.5));
//pa[ii].setY(static_cast<int>(r->second[j] + 0.5));

// The crash was probably caused by writing outside
// pa(total_points + numRings - 1) size, because
// cycle was using ++ii insted of ii++ => reenabled floating point
pa[ii].setX(r->first[j]);
pa[ii].setY(r->second[j]);
pa[j].setX(r->first[j]);
pa[j].setY(r->second[j]);
}

// Store the last point of the first ring, and insert it at
// the end of all other rings. This makes all the other rings
// appear as holes in the first ring.
if (i == 0)
{
outerRingPt.setX(pa[ii-1].x());
outerRingPt.setY(pa[ii-1].y());
}
else
pa[ii++] = outerRingPt;
path.addPolygon(pa);

// Tidy up the pointed to pairs of vectors as we finish with them
delete rings[i];
Expand Down Expand Up @@ -759,32 +730,26 @@ std::cerr << i << ": " << ring->first[i]
myColor = myTransparentPen.color();
myColor.setAlpha(transparencyLevelInt);
myTransparentPen.setColor(myColor);
//
// draw the polygon fill
//

p->setBrush(myTransparentBrush);
p->setPen ( Qt::NoPen ); // no boundary
p->drawPolygon( pa );

// draw the polygon outline. Draw each ring as a separate
// polygon to avoid the lines associated with the outerRingPt.
p->setBrush ( Qt::NoBrush );
p->setPen (myTransparentPen);

ringDetailType::const_iterator ri = ringDetails.begin();

for (; ri != ringDetails.end(); ++ri)
p->drawPolygon(pa.constData() + ri->first, ri->second, Qt::OddEvenFill);

//
// draw the polygon
//
p->drawPath(path);


// draw vertex markers if in editing mode, but only to the main canvas
if (
(mEditable) &&
(drawingToEditingCanvas)
)
{
for(int i = 0; i < pa.size(); ++i)
for(int i = 0; i < path.elementCount(); ++i)
{
drawVertexMarker((int)(pa[i].x()), (int)(pa[i].y()), *p);
const QPainterPath::Element & e = path.elementAt(i);
drawVertexMarker((int)e.x, (int)e.y, *p);
}
}

Expand Down

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