I’m building a simple RPG using Pygame and would like to implement a drag-and-drop inventory. However, even with the consideration of blitting a separate surface, it seems that the entire screen will need to be recalculated every single time the user drags an item around. Would it be best to allow a limited range of motion, or is it simply not feasible to implement such an interface?
I’m building a simple RPG using Pygame and would like to implement a drag-and-drop
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redrawing most or all of the screen is a very normal thing, across all windowing systems. this is rarely an issue, since most objects on screen can be drawn quickly.
To make this practical, it’s necessary to organize all of the game objects that have to be drawn in such a way that they can be quickly found and drawn in the right order. This often means that objects of a particular type are grouped into some sort of layer. The drawing code can go through each layer, and for each object in each layer, ask the object to draw itself. If a particular layer is costly to draw, because it’s got a lot of objects, can store a prerendered surface and blit that instead.
A really simple hack to get a similar effect is to capture the screen at the start of a drag to a surface, and then blit that every frame instead of the whole game. This obviously only makes sense in a game where dragging also means that the rest of the game is effectively paused.