problem rendering garbled when rendering twice (QGraphicsScene->render(..))

[alwin]

I created another image, because I suspected it had something to do with the graphicTask objects (the green and blue rectangles). Some of these objects are partly in the rendered picture and partly outside it. (i.e. boundingRect() is partly outside the image) I shifted these task objects and recreated the image. Now I see that some of the timeline of the first render is also in the second image. This is strange because I use a newly created image (see the code) and render to that.
I also created an image without any task obejcts (only the timeline and the night-time rectangles (the grey rectangles) are in the image. When I do this it does not garble up the second image (see attached test2.jpg)

[wysota]

So how about that example code?

[Bitto]

Make sure to initialize the image. By default it's full of uninitialized pixels, and QGraphicsScene::render() will blend on top (source-over composition). When your app starts, chances are when you create the first image, it's going to be blank because the OS blanks those bits. Second time however, the image is likely to contain junk from the last time you rendered.

See QImage::fill(). Don't know if that will solve the problem but it's worth a shot...

[panly099]

Make sure to initialize the image. By default it's full of uninitialized pixels, and QGraphicsScene::render() will blend on top (source-over composition). When your app starts, chances are when you create the first image, it's going to be blank because the OS blanks those bits. Second time however, the image is likely to contain junk from the last time you rendered.

See QImage::fill(). Don't know if that will solve the problem but it's worth a shot...

This explanation is the right point and helps me out of my struggle. Thanks Bitto.