Get Clicked Point Along QPainterPath
How can I get the percentage representing the point clicked along a QPainterPath. For example say I have a line, like the image below, and a user clicks on the QPainterPath, represented by the red dot. I would like to log what percentage the point falls along the path. In this case it would print 0.75 since the point is located around 75%.
These are the known variables:
# QPainterPath
path = QPainterPath()
path.moveTo( QPointF(10.00, -10.00) )
path.cubicTo(
QPointF(114.19, -10.00),
QPointF(145.80, -150.00),
QPointF(250.00, -150.00)
)
# User Clicked Point
QPointF(187.00, -130.00)
Updated!
My goal is to give the user the ability to click on the path and insert a point. Below is the code i have so far. You'll see in the video that it appears to fail when adding points between points. simply click on the path to insert a point.
Video Link to Watch bug:
import sys
from PySide.QtGui import *
from PySide.QtCore import *
import random, math
class MyGraphicsView(QGraphicsView):
def __init__(self):
super(MyGraphicsView, self).__init__()
self.setDragMode(QGraphicsView.RubberBandDrag)
self.setCacheMode(QGraphicsView.CacheBackground)
self.setHorizontalScrollBarPolicy( Qt.ScrollBarAlwaysOff )
self.setVerticalScrollBarPolicy( Qt.ScrollBarAlwaysOff )
def mousePressEvent(self, event):
item = self.itemAt(event.pos())
if event.button() == Qt.LeftButton and isinstance(item, ConnectionItem):
percentage = self.percentageByPoint(item.shape(), self.mapToScene(event.pos()))
item.addKnotByPercent(percentage)
event.accept()
elif event.button() == Qt.MiddleButton:
super(MyGraphicsView, self).mousePressEvent(event)
# connection methods
def percentageByPoint(self, path, point, precision=0.5, width=3.0):
percentage = -1.0
if path.contains(point):
t = 0.0
d = []
while t <=100.0:
d.append(QVector2D(point - path.pointAtPercent(t/100.0)).length())
t += precision
percentage = d.index(min(d))*precision
return percentage
class MyGraphicsScene(QGraphicsScene):
def __init__(self, parent):
super(MyGraphicsScene, self).__init__()
self.setBackgroundBrush(QBrush(QColor(50,50,50)))
class KnotItem(QGraphicsEllipseItem):
def __init__(self, parent=None,):
super(self.__class__, self).__init__(parent)
self.setAcceptHoverEvents(True)
self.setFlag(self.ItemSendsScenePositionChanges, True)
self.setFlag(self.ItemIsSelectable, True) # false
self.setFlag(self.ItemIsMovable, True) # false
self.setRect(-6, -6, 12, 12)
# Overrides
def paint(self, painter, option, widget=None):
painter.save()
painter.setRenderHint(QPainter.Antialiasing)
painter.setPen(QPen(QColor(30,30,30), 2, Qt.SolidLine))
painter.setBrush(QBrush(QColor(255,30,30)))
painter.drawEllipse(self.rect())
painter.restore()
def itemChange(self, change, value):
if change == self.ItemScenePositionHasChanged:
if self.parentItem():
self.parentItem().update()
return super(self.__class__, self).itemChange(change, value)
def boundingRect(self):
rect = self.rect()
rect.adjust(-1,-1,1,1)
return rect
class ConnectionItem(QGraphicsPathItem):
def __init__(self, startPoint, endPoint, parent=None):
super(ConnectionItem, self).__init__()
self._hover = False
self.setAcceptHoverEvents(True)
self.setFlag( QGraphicsItem.ItemIsSelectable )
self.setFlag(QGraphicsItem.ItemSendsScenePositionChanges, True)
self.setZValue(-100)
self.startPoint = startPoint
self.endPoint = endPoint
self.knots = []
self.update()
def getBezierPath(self, points=[], curving=1.0):
# Calculate Bezier Line
path = QPainterPath()
curving = 1.0 # range 0-1
if len(points) < 2:
return path
path.moveTo(points[0])
for i in range(len(points)-1):
startPoint = points[i]
endPoint = points[i+1]
# use distance as mult, closer the nodes less the bezier
dist = math.hypot(endPoint.x() - startPoint.x(), endPoint.y() - startPoint.y())
# multiply distance by 0.375
offset = dist * 0.375 * curving
ctrlPt1 = startPoint + QPointF(offset,0);
ctrlPt2 = endPoint + QPointF(-offset,0);
# print startPoint, ctrlPt1, ctrlPt2, endPoint
path.cubicTo(ctrlPt1, ctrlPt2, endPoint)
return path
def drawPath(self, pos=None):
# Calculate Bezier Line
points = [self.startPoint]
for k in self.knots:
points.append(k.scenePos())
points.append(self.endPoint)
path = self.getBezierPath(points)
self.setPath(path)
def update(self):
super(self.__class__, self).update()
self.drawPath()
def paint(self, painter, option, widget):
painter.setRenderHints( QPainter.Antialiasing | QPainter.SmoothPixmapTransform | QPainter.HighQualityAntialiasing, True )
pen = QPen(QColor(170,170,170), 2, Qt.SolidLine, Qt.RoundCap, Qt.RoundJoin)
if self.isSelected():
pen.setColor(QColor(255, 255, 255))
elif self.hover:
pen.setColor(QColor(255, 30, 30))
painter.setPen(pen)
painter.drawPath(self.path())
def shape(self):
'''
Description:
This is super important for creating a more accurate path used for
collision detection by cursor.
'''
qp = QPainterPathStroker()
qp.setWidth(15)
qp.setCapStyle(Qt.SquareCap)
return qp.createStroke(self.path())
def hoverEnterEvent(self, event):
self.hover = True
self.update()
super(self.__class__, self).hoverEnterEvent(event)
def hoverLeaveEvent(self, event):
self.hover = False
self.update()
super(self.__class__, self).hoverEnterEvent(event)
def addKnot(self, pos=QPointF(0,0)):
'''
Description:
Add not based on current location of cursor or inbetween points on path.
'''
knotItem = KnotItem(parent=self)
knotItem.setPos(pos)
self.knots.append(knotItem)
self.update()
def addKnotByPercent(self, percentage=0.0):
'''
Description:
The percentage value should be between 0.0 and 100.0. This value
determines the location of the point and it's index in the knots list.
'''
if percentage < 0.0 or percentage > 100.0:
return
# add item
pos = self.shape().pointAtPercent(percentage*.01)
knotItem = KnotItem(parent=self)
knotItem.setPos(pos)
index = int(len(self.knots) * (percentage*.01))
print len(self.knots), (percentage), index
self.knots.insert(index, knotItem)
self.update()
# properties
@property
def hover(self):
return self._hover
@hover.setter
def hover(self, value=False):
self._hover = value
self.update()
class MyMainWindow(QMainWindow):
def __init__(self):
super(MyMainWindow, self).__init__()
self.setWindowTitle("Test")
self.resize(800,600)
self.gv = MyGraphicsView()
self.gv.setScene(MyGraphicsScene(self))
self.btnReset = QPushButton('Reset')
lay_main = QVBoxLayout()
lay_main.addWidget(self.btnReset)
lay_main.addWidget(self.gv)
widget_main = QWidget()
widget_main.setLayout(lay_main)
self.setCentralWidget(widget_main)
self.populate()
# connect
self.btnReset.clicked.connect(self.populate)
def populate(self):
scene = self.gv.scene()
for x in scene.items():
scene.removeItem(x)
del x
con = ConnectionItem(QPointF(-150,150), QPointF(250,-150))
scene.addItem(con)
def main():
app = QApplication(sys.argv)
ex = MyMainWindow()
ex.show()
sys.exit(app.exec_())
if __name__ == '__main__':
main()
Solution
A possible solution is to use pointAtPercent () that returns a given point a percentage and calculate the distance to the point and find the minimum index and multiply it by the step. But for this the search must be refined because the previous algorithm works for any point even if it is outside the path. The idea in this case is to use a QPainterPath with a certain area using QPainterPathStroker and verify if the point belongs, and if not the value is outside the QPainterPath.
C++
#include <QtGui>
static qreal percentageByPoint(const QPainterPath & path, const QPointF & p, qreal precision=0.5, qreal width=3.0){
qreal percentage = -1;
QPainterPathStroker stroker;
stroker.setWidth(width);
QPainterPath strokepath = stroker.createStroke(path);
if(strokepath.contains(p)){
std::vector<qreal> d;
qreal t=0.0;
while(t<=100.0){
d.push_back(QVector2D(p - path.pointAtPercent(t/100)).length());
t+= precision;
}
std::vector<qreal>::iterator result = std::min_element(d.begin(), d.end());
int j= std::distance(d.begin(), result);
percentage = j*precision;
}
return percentage;
}
int main(int argc, char *argv[])
{
Q_UNUSED(argc)
Q_UNUSED(argv)
QPainterPath path;
path.moveTo( QPointF(10.00, -10.00) );
path.cubicTo(
QPointF(114.19, -10.00),
QPointF(145.80, -150.00),
QPointF(250.00, -150.00)
);
// User Clicked Point
QPointF p(187.00, -130.00);
qreal percentage = percentageByPoint(path, p);
qDebug() << percentage;
return 0;
}
python:
def percentageByPoint(path, point, precision=0.5, width=3.0):
percentage = -1.0
stroker = QtGui.QPainterPathStroker()
stroker.setWidth(width)
strokepath = stroker.createStroke(path)
if strokepath.contains(point):
t = 0.0
d = []
while t <=100.0:
d.append(QtGui.QVector2D(point - path.pointAtPercent(t/100)).length())
t += precision
percentage = d.index(min(d))*precision
return percentage
if __name__ == '__main__':
path = QtGui.QPainterPath()
path.moveTo(QtCore.QPointF(10.00, -10.00) )
path.cubicTo(
QtCore.QPointF(114.19, -10.00),
QtCore.QPointF(145.80, -150.00),
QtCore.QPointF(250.00, -150.00)
)
point = QtCore.QPointF(187.00, -130.00)
percentage = percentageByPoint(path, point)
print(percentage)
Output:
76.5
Instead of implementing the logic in QGraphicsView, you must do it in the item, and then when you update the path, the points must be ordered with respect to the percentage.
import math
from PySide import QtCore, QtGui
from functools import partial
class MyGraphicsView(QtGui.QGraphicsView):
def __init__(self):
super(MyGraphicsView, self).__init__()
self.setDragMode(QtGui.QGraphicsView.RubberBandDrag)
self.setCacheMode(QtGui.QGraphicsView.CacheBackground)
self.setHorizontalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)
self.setVerticalScrollBarPolicy(QtCore.Qt.ScrollBarAlwaysOff)
scene = QtGui.QGraphicsScene(self)
scene.setBackgroundBrush(QtGui.QBrush(QtGui.QColor(50,50,50)))
self.setScene(scene)
class KnotItem(QtGui.QGraphicsEllipseItem):
def __init__(self, parent=None,):
super(self.__class__, self).__init__(parent)
self.setAcceptHoverEvents(True)
self.setFlag(self.ItemSendsScenePositionChanges, True)
self.setFlag(self.ItemIsSelectable, True)
self.setFlag(self.ItemIsMovable, True)
self.setRect(-6, -6, 12, 12)
self.setPen(QtGui.QPen(QtGui.QColor(30,30,30), 2, QtCore.Qt.SolidLine))
self.setBrush(QtGui.QBrush(QtGui.QColor(255,30,30)))
def itemChange(self, change, value):
if change == self.ItemScenePositionHasChanged:
if isinstance(self.parentItem(), ConnectionItem):
self.parentItem().updatePath()
# QtCore.QTimer.singleShot(60, partial(self.parentItem().setSelected,False))
return super(self.__class__, self).itemChange(change, value)
class ConnectionItem(QtGui.QGraphicsPathItem):
def __init__(self, startPoint, endPoint, parent=None):
super(ConnectionItem, self).__init__(parent)
self._start_point = startPoint
self._end_point = endPoint
self._hover = False
self.setAcceptHoverEvents(True)
self.setFlag(QtGui.QGraphicsItem.ItemIsSelectable )
self.setFlag(QtGui.QGraphicsItem.ItemSendsScenePositionChanges)
self.setZValue(-100)
self.updatePath()
def updatePath(self):
p = [self._start_point]
for children in self.childItems():
if isinstance(children, KnotItem):
p.append(children.pos())
p.append(self._end_point)
v = sorted(p, key=partial(ConnectionItem.percentageByPoint, self.path()))
self.setPath(ConnectionItem.getBezierPath(v))
def paint(self, painter, option, widget):
painter.setRenderHints(QtGui.QPainter.Antialiasing | QtGui.QPainter.SmoothPixmapTransform | QtGui.QPainter.HighQualityAntialiasing, True )
pen = QtGui.QPen(QtGui.QColor(170,170,170), 2, QtCore.Qt.SolidLine, QtCore.Qt.RoundCap, QtCore.Qt.RoundJoin)
if self.isSelected():
pen.setColor(QtGui.QColor(255, 255, 255))
elif self._hover:
pen.setColor(QtGui.QColor(255, 30, 30))
painter.setPen(pen)
painter.drawPath(self.path())
def mousePressEvent(self, event):
if event.button() == QtCore.Qt.LeftButton:
item = KnotItem(parent=self)
item.setPos(event.pos())
def hoverEnterEvent(self, event):
self._hover = True
self.update()
super(self.__class__, self).hoverEnterEvent(event)
def hoverLeaveEvent(self, event):
self._hover = False
self.update()
super(self.__class__, self).hoverEnterEvent(event)
def shape(self):
qp = QtGui.QPainterPathStroker()
qp.setWidth(15)
qp.setCapStyle(QtCore.Qt.SquareCap)
return qp.createStroke(self.path())
@staticmethod
def getBezierPath(points=[], curving=1.0):
# Calculate Bezier Line
path = QtGui.QPainterPath()
curving = 1.0 # range 0-1
if len(points) < 2:
return path
path.moveTo(points[0])
for i in range(len(points)-1):
startPoint = points[i]
endPoint = points[i+1]
# use distance as mult, closer the nodes less the bezier
dist = math.hypot(endPoint.x() - startPoint.x(), endPoint.y() - startPoint.y())
# multiply distance by 0.375
offset = dist * 0.375 * curving
ctrlPt1 = startPoint + QtCore.QPointF(offset,0);
ctrlPt2 = endPoint + QtCore.QPointF(-offset,0);
# print startPoint, ctrlPt1, ctrlPt2, endPoint
path.cubicTo(ctrlPt1, ctrlPt2, endPoint)
return path
@staticmethod
def percentageByPoint(path, point, precision=0.5):
t = 0.0
d = []
while t <=100.0:
d.append(QtGui.QVector2D(point - path.pointAtPercent(t/100.0)).length())
t += precision
percentage = d.index(min(d))*precision
return percentage
class MyMainWindow(QtGui.QMainWindow):
def __init__(self):
super(MyMainWindow, self).__init__()
central_widget = QtGui.QWidget()
self.setCentralWidget(central_widget)
button = QtGui.QPushButton("Reset")
self._view = MyGraphicsView()
button.clicked.connect(self.reset)
lay = QtGui.QVBoxLayout(central_widget)
lay.addWidget(button)
lay.addWidget(self._view)
self.resize(640, 480)
self.reset()
@QtCore.Slot()
def reset(self):
self._view.scene().clear()
it = ConnectionItem(QtCore.QPointF(-150,150), QtCore.QPointF(250,-150))
self._view.scene().addItem(it)
def main():
import sys
app =QtGui.QApplication(sys.argv)
ex = MyMainWindow()
ex.show()
sys.exit(app.exec_())
main()
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