Painting over a QGLWidget fails

neon29

I am trying to paint over a QGLWidget by means of a QPainter as explained in various tutorials. In my paintGL() function, I have two cases. Indeed, if there is nothing to draw in OpenGL then I only use the QPainter to draw 2 lines (this part does work). However, when there is something to draw with OpenGL, I first use an OpenGL function such as drawElements() and then I use my painter to overpaint the widget, but in this case I can only display my OpenGL "objects", the two lines being invisible.

Here is the code of my paintGL method:

def paintGL(self): 


        glClearColor(0, 0, 0, 1)
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)



        if np.array(self.objects).size:

            print('there are %i objects'%(len(self.objects)))
            #                


            # active shader program
            glUseProgram(self.shaderProgram)

            for i, obj in enumerate(self.objects):        

                loc_pos = glGetAttribLocation(self.shaderProgram, "position")
                glEnableVertexAttribArray(loc_pos)
                glBindBuffer(GL_ARRAY_BUFFER, obj.VBO[0])
                glVertexAttribPointer(loc_pos, 2, GL_FLOAT, False, 0,  ctypes.c_void_p(0))

                loc_col = glGetAttribLocation(self.shaderProgram, "color")
                glEnableVertexAttribArray(loc_col)

                glBindBuffer(GL_ARRAY_BUFFER, obj.VBO[1])
                glVertexAttribPointer(loc_col, 4, GL_FLOAT, False, 0,  ctypes.c_void_p(0))


                glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, obj.VBO[2])
                glDrawElements(GL_TRIANGLES, obj.indices.size, GL_UNSIGNED_INT, ctypes.c_void_p(0))


            glUseProgram(0)


            painter = QtGui.QPainter()
            painter.begin(self)
            painter.setRenderHint(QtGui.QPainter.Antialiasing)
            print(painter.isActive())


            pen = QtGui.QPen(QtGui.QColor(255,0,0), 10)

            x = 100
            y= 100       

            # clean previous drawings        
            painter.fillRect(self.rect(),QtGui.QBrush(QtGui.QColor(0,0,0)) )
            painter.setPen(pen)

            currentFont = painter.font()
            currentFont.setPointSize(currentFont.pointSize()*4)
            painter.setFont(currentFont)
            painter.drawLine(x, 0, x, self.height())
            painter.drawLine(0, y, self.width(), y)    


            painter.end()

        else:

            print('No data in objects ==> no drawing')
            painter = QtGui.QPainter()
            painter.begin(self)
            painter.setRenderHint(QtGui.QPainter.Antialiasing)
            print(painter.isActive())


            pen = QtGui.QPen(QtGui.QColor(255,0,0), 10)

            x = 100
            y= 100       

            # clean previous drawings        
            painter.fillRect(self.rect(),QtGui.QBrush(QtGui.QColor(0,0,0)) )
            painter.setPen(pen)

            currentFont = painter.font()
            currentFont.setPointSize(currentFont.pointSize()*4)
            painter.setFont(currentFont)
            painter.drawLine(x, 0, x, self.height())
            painter.drawLine(0, y, self.width(), y)    


            painter.end()