Viewport vs. World Coordinate Systems

Game Mechanics
#1

Right now my side scroller game demo basically moves my map and all objects around my player, ie. the viewport and the player don’t actually move, everything else moves around it.

I would like to change this if I can so that the player and the viewport move around together and the map and all other objects stay stationary. I know that when I draw using my Graphics2D object, I am currently using coordinates starting at the origin (0, 0) located in the top left hand corner of my JPanel extended canvas.

So my question is, how would I be able to map a viewport to move around, and have access to world cooridinates, the 2D playable world being updated and not rendered much bigger than the viewport size. Also having access to a set of viewport cooridnates would be nice.

Does anyone have any tips on how I can implement something along these lines using Graphics2D.

Currently I am using the wrap around background technique, but I would like to change this to a stationary map with moving player and viewport in sync.

#2

At it’s simplest, a viewport is a pair of world coordinates representing the offset along the x and y axis. When you render, you’ll subtract those offsets from the world coordinates of your objects to get the screen coordinates.

You may have a little trouble if your screen y axis is going up -> down while your world y-axis is going up -> down. In that case, screenY = screenHeight - (worldY - viewY) instead of just screenY = worldY - viewY.

That’s assuming your screen origin is in a corner, if it’s not, you’ll have to offset by wherever it is… It’ll also get a little more involved if you want to scale (i.e., if 1 unit of world coordinates != 1 pixel), but it’s the same general idea of converting from world to screen coordinates.