Draw line: retrieve the covered pixels - pyqt

Question

I want to draw a line on a widget:
from PyQt4 import QtGui, QtCore
class LineLabel(QtGui.QLabel):
def __init__(self,parent=None):
super(LineLabel,self).__init__(parent)
self.setMinimumSize(100,100)
self.setMaximumSize(100,100)
def paintEvent(self,e):
painter=QtGui.QPainter(self)
pen = QtGui.QPen()
pen.setWidth(5)
painter.setPen(pen)
painter.drawLine(10,10,90,90)
painter.end()
def test():
form = QtGui.QWidget()
label = LineLabel(form)
form.show()
return form
import sys
app = QtGui.QApplication(sys.argv)
window =test()
sys.exit(app.exec_())
What is the best way to get a list of the pixels that are covered by the line?
Update from the comments:
I don't need to know the pixels directly in between the start and end point but all those pixels that are changed to black (which are more pixels because the line has a certain width).
My overall goal is a fast way to know which pixels on the widget are black. Iterating over the pixels of the image and querying the color is much slower than reading the color value from a list in which the colors are stored: For me 1.9 seconds for an image with 1 million pixels to 0.23 seconds for a list with 1 million entries. Therefore I must update that list after every change of the image on the widget such as by drawing a line.
Answers that refer to a QGraphicsItem in a QGraphicsScene are also helpful.

Answer 1

You may use a linear equation to find the point you want in the line. I think that there is no reference to a draw line.
from PyQt4 import QtGui
from PyQt4.QtGui import QColor, QPaintEvent
m_nInitialX = 0.0
m_nInitialY = 0.0
# my line abstraction
class MyLine:
x1, y1, x2, y2 = .0, .0, .0, .0
width = .0
px, py = (.0, .0)
draw_point = False
def __init__(self, x1, y1, x2, y2, width):
self.x1, self.y1, self.x2, self.y2 = (x1, y1, x2, y2)
self.width = width
def is_in_line(self, x, y):
# mark a position in the line
m = (self.y2 - self.y1) / (self.x2 - self.x1)
print(m*(x-self.x1)-(y-self.y1))
if abs((m*(x-self.x1) - (y-self.y1))) <= self.width/2:
self.draw_point = True
return True
else:
return False
def add_red_point(self, x, y):
self.px, self.py = (x, y)
def draw(self, widget):
painter = QtGui.QPainter(widget)
pen = QtGui.QPen()
pen.setWidth(self.width)
painter.setPen(pen)
painter.drawLine(self.x1, self.y1, self.y2, self.y2)
if self.draw_point:
pen.setColor(QColor(255, 0, 0))
painter.setPen(pen)
painter.drawPoint(self.px, self.py)
painter.end()
line = MyLine(10, 10, 90, 90, width=10) # <-- my line abstraction
class LineLabel(QtGui.QLabel):
def __init__(self, parent=None):
super(LineLabel, self).__init__(parent)
self.setMinimumSize(100, 100)
self.setMaximumSize(100, 100)
# always redraw when needed
def paintEvent(self, e):
print("draw!")
line.draw(self)
def mousePressEvent(self, event):
# mark clicked position in line
m_nInitialX = event.pos().x()
m_nInitialY = event.pos().y()
if line.is_in_line(m_nInitialX, m_nInitialY):
line.add_red_point(m_nInitialX, m_nInitialY)
self.repaint()
def test():
form = QtGui.QWidget()
label = LineLabel(form)
form.show()
return form
import sys
app = QtGui.QApplication(sys.argv)
window = test()
sys.exit(app.exec_())