There are many topics like this, but none with concrete answers. I am drawing a tile-map in the traditional way (two for loops) and keeping my player centered except when the edges of the map is reached. How would I create collision detection? I need to know how to translate tile location in the array to screen coordinates I think.
A:
It depends on the model.
If your model (the data) is a grid, then a collision occurs simply when two incompatible objects occupy the same location. The easiest way to handle this type of collision is just to make sure where you are trying to move a game entity to is "available". If it is, no collision, and update the model. If it wasn't free, then there was a collision.
The screen simply renders the model. With the exception of something like of per-pixel collision detection (think the original lemmings or worms), don't use it for collision detection.
The screen/view is just the rendering agent. While you can have the model tied tightly to the screen (e.g. you only need to update parts of the screen in which things have changed such as when a piece is moved), the screen is not, and should not, generally be considered part of the model. However, with modern computing speed, you might as well simple re-render the entire visible model each frame.
(Yes, I know I repeated myself. It was on purpose.)
Now, to answer the secondary question not mentioned in the title:
When you start rendering, simply draw screen_width/cell_width/2 cells to the left and screen_width/cell_width/2 cells to the right of the player (the player is assumed to take 1x1). Do the same for the up-and-down. Make sure to not cause an Index-Out-Of-Bounds exception. You can run the for-loops with out-of-bounds values, as long long as you clamp/filter before using them. If you wish to only make the character "push" the edge when he gets close, keep track of a current model-to-view reference as well.
pst
2010-04-05 05:15:00