[PyOpenGL-Users] Crossfade images

[Frédéric <fre...@gb...>]

Hi,

I'm new to OpenGL, and I need your help to start a project: an open-source  
cross-platform photo slideshow software, like Pictures-To-Exe[1], 
ProShow[2] or m.objects[3]. It will probably be a mix of their main 
features.

I started to write the engine, using PyQt4, which has nice features for both 
audio and display. Here is the part of the code I currently use to draw the 
images with their respective luminosity, to simulate the projectors:

class PreviewDialogObject(QtGui.QWidget):
    def __init__(self, projectors):
        QtGui.QWidget.__init__(self)

        self.__projectors = projectors

        layout = QtGui.QHBoxLayout()
        self.__previewLabel = QtGui.QLabel("Preview")
        layout.addWidget(self.__previewLabel)
        self.setLayout(layout)

        self.resize(WIDTH, HEIGHT)

    def refresh(self):
        image = QtGui.QImage(WIDTH, HEIGHT,
                             QtGui.QImage.Format_ARGB32_Premultiplied)
        painter = QtGui.QPainter(image)
        painter.setCompositionMode(QtGui.QPainter.CompositionMode_Source)
        painter.fillRect(QtCore.QRect(0, 0, WIDTH, HEIGHT), QtCore.Qt.black)
        painter.setCompositionMode(QtGui.QPainter.CompositionMode_Screen)
        for d in self.__projectors.itervalues():
            painter.setOpacity(d['opacity'])
            painter.drawImage((WIDTH - d['image'].width()) / 2,
                              (HEIGHT - d['image'].height()) / 2,
                               d['image'])
        painter.end()
        self.__previewLabel.setPixmap(QtGui.QPixmap.fromImage(image))

But even on my fast machine (quad core Q6600), I get some flickering ; so I 
think I need to switch to OpenGL to get very smooth transitions.

I found some code on the web to use a QGLWidget, instead of the QWidget:

class PreviewDialogGLObject(QtGui.QGraphicsView):
    def __init__(self, projectors):
        QtGui.QGraphicsView.__init__(self)

        self.__projectors = projectors
        format = QtOpenGL.QGLFormat()
        format.setSampleBuffers(True)
        format.setDoubleBuffer(True)
        widget = QtOpenGL.QGLWidget(format)
        self.setViewport(widget)
        self.setViewportUpdateMode(QtGui.QGraphicsView.FullViewportUpdate)
        self.__previewScene = PreviewScene(self.__projectors)
        self.setScene(self.__previewScene)

        self.resize(WIDTH, HEIGHT)

    def refresh(self):
        self.__previewScene.update()


class PreviewScene(QtGui.QGraphicsScene):
    def __init__(self, projectors):
        QtGui.QGraphicsScene.__init__(self)

        self.__projectors = projectors

    def drawBackground(self, painter, rect):
        painter.save()
        painter.setCompositionMode(QtGui.QPainter.CompositionMode_Source)
        painter.fillRect(QtCore.QRect(-WIDTH / 2, -HEIGHT / 2,
                                      WIDTH, HEIGHT),
                                      QtCore.Qt.black)
        #painter.setCompositionMode(QtGui.QPainter.CompositionMode_Screen)
        painter.setCompositionMode(QtGui.QPainter.CompositionMode_Source)
        for d in self.__projectors.itervalues():
            painter.setOpacity(d['opacity'])
            painter.drawImage(-d['image'].width() / 2,
                              -d['image'].height() / 2,
                              d['image'])
        painter.restore()

But it does not improve anything at all! I get the same issue. The only 
difference is that I can't use the 'Screen' composition mode anymore :o/

This is why I'm here! I guess that I have to use native OpenGL functions in 
the drawBackground() method, to crossfade my images. But I can't get it 
work. I spent days on the web looking at tutorials or books, but I'm lost. 
I understand that I need to use textures, but all tutorials use different 
methods, and my tests does not lead to anything usable (it takes several 
seconds to refresh a simple image!). More, I think I should start using 
OpenGL3, but all functions used in the tutorials are deprecated, and I 
didn't find any information for replacement.

So, it would be nice if someone could help me to start, with bases.

I also would like to know if OpenGL will allow me to use complex composition 
modes, like 'screen' or 'addition', to simulate different projection 
results?

Thanks for reading,

[1] http://www.wnsoft.com/apr/index.html
[2] http://www.photodex.com/products/proshowgold
[3] http://www.mobjects.com

-- 
   Frédéric

   http://www.gbiloba.org