Question regarding image tiling in a QGraphicsView

Question

This is related to one of my other questions.

If I am tiling a large image by creating a separate QGraphicsItem (with the raster data as its pixmap), how do I keep track of the QGraphicsItem's position within the scene? Obviously for raster data, it is important to keep all the tiles "touching" to make a continuous image and they also have to be in the right place so the image doesnt look jumbled.

Does each tile have to have positioning methods that move it in relation to it's neighbors on the top/left/bottom/right? This seems kind of clunky. Is there a better way to make them all move together?

In other words, if I pan the scene with scroll bars, or pick up the image and drag/move it around in the scene, I want all the tiles to also move and stay in the right position relative to each other.

What is the best approach for controlling the layout, which tiles need to be rendered (i.e. only the visible ones), and populating the data only once it is needed? Also, once a tile has been rendered, is the data from it ever dropped, and repopulated from the image file, say if it stays out of view for a while, then comes back later if someone pans to that section?

Answer 1

There are (more than) 2 ways of doing this:

1. Use QGraphicsItemGroup which handles grouping of your tile items for you. It moves, selects, updates it's group members as if they are one. I've never used it but from the doc, it seems to work with typical applications.

2. Paint the tiles yourself in the paint() of one custom item. This gives you total control on how to place and draw the tiles while the item truly acts as one item since it is, well, one item. This is what I do.