Drag and drop a point on the canvas - pyqt

Question

How could I use drag and drop techniqe on a point which is on a QCanvas? I don't really find any slot on the canvas to connect the mouse click.
class Canvas(QtGui.QWidget):
def __init__(self, parent):
super(Canvas, self).__init__(parent)
self.setGeometry(0,0,200,200)
def paintEvent(self, e):
qp = QtGui.QPainter()
qp.begin(self)
self.drawPoints(qp)
qp.end()
def drawPoints(self, qp):
qp.setPen(QtCore.Qt.red)
size = self.size()
#test
x = 0
y = 0
for k in range(0,150,2):
qp.drawPoint(x,y)
x += 5
y += 5
#get the click coordinates
def mousePressEvent(self, QMouseEvent):
print QMouseEvent.pos()

Answer 1

The drag an drop technique is more or less like this:
On click: Identify the dragging object
On move: redraw the dragging object
On release: update the final state
On the step 2 you can also update the canvas. This is an example of the technique. I use numpy to manage the points (hope don't bother you).
from PyQt4 import QtGui,QtCore
import numpy as np
class Canvas(QtGui.QWidget):
DELTA = 10 #for the minimum distance
def __init__(self, parent):
super(Canvas, self).__init__(parent)
self.draggin_idx = -1
self.setGeometry(0,0,200,200)
self.points = np.array([[v*5,v*5] for v in range(75)], dtype=np.float)
def paintEvent(self, e):
qp = QtGui.QPainter()
qp.begin(self)
self.drawPoints(qp)
qp.end()
def drawPoints(self, qp):
qp.setPen(QtCore.Qt.red)
for x,y in self.points:
qp.drawPoint(x,y)
def _get_point(self, evt):
return np.array([evt.pos().x(),evt.pos().y()])
#get the click coordinates
def mousePressEvent(self, evt):
if evt.button() == QtCore.Qt.LeftButton and self.draggin_idx == -1:
point = self._get_point(evt)
#dist will hold the square distance from the click to the points
dist = self.points - point
dist = dist[:,0]**2 + dist[:,1]**2
dist[dist>self.DELTA] = np.inf #obviate the distances above DELTA
if dist.min() < np.inf:
self.draggin_idx = dist.argmin()
def mouseMoveEvent(self, evt):
if self.draggin_idx != -1:
point = self._get_point(evt)
self.points[self.draggin_idx] = point
self.update()
def mouseReleaseEvent(self, evt):
if evt.button() == QtCore.Qt.LeftButton and self.draggin_idx != -1:
point = self._get_point(evt)
self.points[self.draggin_idx] = point
self.draggin_idx = -1
self.update()
app = QtGui.QApplication([])
c = Canvas(None)
c.show()
app.exec_()