QGLWidget don't move its contents on scroll

Question

I'm using Qt from python with PySide bindings. The main part of my application is the OpenGL view that can be resized to particular value (this is a simulator for testing my game in different resolutions of mobile devices). I use QGLWidget to render graphics from my game engine and QScrollArea for scrolling.

When I try to scroll GL view nothing happens - it just stays at the same place, but coordinates of QGLWidget are updated just fine which I see through print statements.

Playing around with resizing main window I've came to conclusion that everything inside QGLWidget is snapped to the bottom-left corner of currently visible area. So this would explain why I can't see scrolling.

Am I supposed to update projection matrix manually?

So you have `QGLWidget` inside `QScrollArea`? What exactly do you expect to happen when you scroll? — Fenikso, Jan 08 '14 at 13:18
I expect that QGLWidget is moved with all it's drawings. I can move QGLWidget around by scaling the window. ScrollView alignment is set center and QGLWidget keeps centered in the window. But I can't move QGLWidget by scrolling, all GL drawings are snapped to bottom-left corner of currently visible rect of QGLWidget. — Vavius, Jan 08 '14 at 18:30

Fenikso · Accepted Answer · 2014-01-09T09:10:58.577

It sounds like some kind of parenting issue. This works as expected:

import sys
from PySide.QtGui import *
from PySide.QtOpenGL import *
from OpenGL.GL import *
from OpenGL.GLU import *

class GLWidget(QGLWidget):
    def __init__(self, *args, **kwargs):
        QGLWidget.__init__(self,  *args, **kwargs)

    def initializeGL(self):
        glShadeModel(GL_SMOOTH)
        glEnable(GL_DEPTH_TEST)
        glClearColor(0.0, 0.0, 0.0, 1.0)
        glClearDepth(1.0)

    def resizeGL(self, w, h):
        glMatrixMode(GL_PROJECTION)
        glLoadIdentity()
        glViewport(0, 0, w, h)
        gluPerspective(45.0, w / h, 1, 1000)

    def paintGL(self):
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
        glMatrixMode(GL_MODELVIEW)
        glLoadIdentity()                   
        glTranslatef(0.0, 0.0, -6.0)            
        glBegin(GL_TRIANGLES)                 
        glColor3f(1.0, 0.0, 0.0)           
        glVertex3f(0.0, 1.0, 0.0)        
        glColor3f(0.0, 0.0, 1.0)           
        glVertex3f(-1.0, -1.0, 0.0)        
        glColor3f(0.0, 1.0, 0.0)           
        glVertex3f(1.0, -1.0, 1.0)        
        glEnd()

class Window(QWidget):
    def __init__(self, *args, **kwargs):
        QWidget.__init__(self, *args, **kwargs)

        self.scroll = QScrollArea(self)
        self.glWidget = GLWidget(self.scroll)
        self.glWidget.resize(600, 400)
        self.scroll.setWidget(self.glWidget)

        self.layout = QHBoxLayout()
        self.layout.addWidget(self.scroll)

        self.setLayout(self.layout)
        self.resize(400, 300)
        self.show()

app = QApplication(sys.argv)
win = Window()
sys.exit(app.exec_())

OS: Windows 7 SP1 (32bit)
PySide: 1.2.1
Qt: 4.8.5
PyOpenGL: 3.0.2

Now it sounds like problem with my setup. I'm using PySide 1.2.1, Qt 4.8.5, Mac OS X 10.8.5. Your triangle is fixed and doesn't move with scroll bars — Vavius, Jan 08 '14 at 20:47
I am on Windows 7. Library versions seem the same, I can check PyOpenGL version tomorrow. — Fenikso, Jan 08 '14 at 21:38
Maybe this problem is related to Cocoa limitations when dealing with GLViews. Here is the line from Qt docs about it: "QGLWidget can’t have any sibling widgets placed ontop of itself. This is due to limitations in the Cocoa API and is not supported by Apple." — Vavius, Jan 08 '14 at 21:45
May be interesting to try the same in Java with Swing and JOGL. Because there are `GLCanvas` and `GLJPanel`. The second being slower but with better compatibility with Swing GUI. I suspect the first to behave the same if it is OS limitation. — Fenikso, Jan 09 '14 at 09:17

QGLWidget don't move its contents on scroll

1 Answers1