Unable to clear OpenGL viewport

Question

I copied this script (pasted below) and ran it. Unfortunately, the image appears scrambled, as below. Can anyone help me get rid of that?

Config:

• Ubuntu 13.10
• Pyopengl 3.0.1b1
• graphic card AMD Radeon HD 6650M

• OpenGL version string: 3.0 Mesa 10.3.0-devel (git-32c5544 saucy-oibaf-ppa)

  from OpenGL.GL import *
  from PyQt4 import QtGui
  from PyQt4.QtOpenGL import *
  
      class WfWidget(QGLWidget):
          def __init__(self, parent = None):
              super(WfWidget, self).__init__(parent)
  
          def paintGL(self):
              glClearColor(0,0,0,0)
              glColor3f(0.0, 0.0, 1.0)
              glRectf(-5, -5, 5, 5)
              glColor3f(1.0, 0.0, 0.0)
              glBegin(GL_LINES)
              glVertex3f(0, 0, 0)
              glVertex3f(20, 20, 0)
              glEnd()
  
          def resizeGL(self, w, h):
              glMatrixMode(GL_PROJECTION)
              glLoadIdentity()
              glOrtho(-50, 50, -50, 50, -50.0, 50.0)
              glViewport(0, 0, w, h)
  
          def initializeGL(self):
              glClearColor(0.0, 0.0, 0.0, 1.0)
              glClear(GL_COLOR_BUFFER_BIT)
  
  if __name__ == '__main__':
      app = QtGui.QApplication(["Winfred's PyQt OpenGL"])
      widget = WfWidget()
      widget.show()
      app.exec_()
  

Answer 1

Move, glClear to the paint method:

def paintGL(self):
    glClear(GL_COLOR_BUFFER_BIT)
    glColor3f(0.0, 0.0, 1.0)
    glRectf(-5, -5, 5, 5)
    glColor3f(1.0, 0.0, 0.0)
    glBegin(GL_LINES)
    glVertex3f(0, 0, 0)
    glVertex3f(20, 20, 0)
    glEnd()

Also here:

    def initializeGL(self):
        glColor3f(0.0, 0.0, 1.0)

you don't need glClear here. Produces: