I've created a simple application (see below) that draws a bezier curve. I
want to give the user the ability to select the curve so they can move it
around. However, I'm having trouble selecting the curve in an intuitive
fashion. When I click on the curve, the point I click on is actually far
away from the curve.
For example, when I click on the left end of the curve, the x-coordinate of
the point where I clicked is about 100 pixels away from the x-coordinate of
the point of the curve I clicked on.
The code below demonstrates this problem.
Any ideas why this is happening or what I'm doing wrong?
Thanks!
Tom
<code>
from math import sqrt
from sys import argv
from PyQt4.Qt import QApplication
from PyQt4.QtCore import QPointF, Qt
from PyQt4.QtGui import (
QColor,
QGraphicsItem,
QGraphicsView,
QGraphicsScene,
QPainterPath,
)
class View(QGraphicsView):
def __init__(self, parent=None):
super(View, self).__init__(parent)
self.epsilon = 11.0
self.graphics_scene = QGraphicsScene(self)
self.setScene(self.graphics_scene)
self.add_curve()
def mousePressEvent(self, event):
if event.button() == Qt.LeftButton:
self.select_item_at(event.x(), event.y())
def select_item_at(self, x, y):
self.unselect_items()
for item in self.items():
if item.contains_point(x, y, self.epsilon):
item.set_selected(True)
item.update()
def unselect_items(self):
for item in self.items():
item.set_selected(False)
item.update()
def add_curve(self):
color = QColor(255, 0, 0)
x0 = 600.0
y0 = 400.0
x1 = 800.0
y1 = 500.0
x2 = 1000.0
y2 = 500.0
x3 = 1200.0
y3 = 400.0
control_points = (QPointF(x0, y0), QPointF(x1, y1),
QPointF(x2, y2), QPointF(x3, y3))
curve = Curve(color, control_points)
self.graphics_scene.addItem(curve)
class Curve(QGraphicsItem):
def __init__(self, color, control_points, parent=None, scene=None):
super(Curve, self).__init__(parent, scene)
self.selected = False
self.color = color
self.path = QPainterPath()
self.path.moveTo(control_points[0])
self.path.cubicTo(*control_points[1:])
def set_selected(self, selected):
self.selected = selected
def contains_point(self, x, y, epsilon):
p = (x, y)
min_distance = float(0x7fffffff)
t = 0.0
while t < 1.0:
point = self.path.pointAtPercent(t)
spline_point = (point.x(), point.y())
print p, spline_point
distance = self.distance(p, spline_point)
if distance < min_distance:
min_distance = distance
t += 0.1
print min_distance, epsilon
return (min_distance <= epsilon)
def boundingRect(self):
return self.path.boundingRect()
def paint(self, painter, option, widget):
painter.setPen(self.color)
painter.setBrush(self.color)
painter.strokePath(self.path, painter.pen())
def distance(self, p0, p1):
a = p1[0] - p0[0]
b = p1[1] - p0[1]
return sqrt(a * a + b * b)
if __name__ == '__main__':
app = QApplication(argv)
view = View()
view.setGeometry(100, 100, 1600, 900)
view.setWindowTitle('MainWindow')
view.show()
app.exec_()
</code>
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