Centring Sprite or moving camera? C++/Opengl

Question

I'm self learning C++ and playing around 2D tile mapping.

I have been reading through this scrolling post here, which is based on this tiling tutorial.

Using the above tutorial and some help from the Pearson, Computer Graphics with OpenGL book I have written a small program that draws a 40x40 tiled world and a Sprite (also a tile).

In terms of drawing/render order, the map(or world) itself is that back layer and the Sprite is the forward most (or top) layer. I'm assuming that's a good way of doing it as its easier for 2 tiles to interact than a tile and a custom sprite or rectangle. Is that correct?

I have implemented a Keyhandling() function that lets you move the map inside the viewport using the keyboards arrow keys. I have a variable called offsetx, offsety that when a key is pressed increases or decreases. Depending on whether I assign the variable to the map or sprite, I can more one or the other in any direction on the screen.

Neither seems to work very well, so I assigned the variables to both (map and sprite) but with positive values for the sprite, and negative for the map. So upon a key press, this allows my Sprite to move in one direction whilst the map moves in the opposite direction.

My problem is, the sprite soon moves enough to leave the window and not enough to bring the more of the map into the scene. (The window only shows about 1/8th of the tiles at any one time).

I've been thinking all day, and I think an efficient/effective way to solve this issue would be to fix the sprite to the centre of the screen and when a key is pressed the map moves around... I'm unsure how to implement this though.

Would that be a good way? Or is it expected to move the viewport or camera too?

Answer 1

You don't want to move everything relative to the Sprite whenever your character moves. Consider a more complicated world where you also have other things on the map, eg other sprites. It's simplest to keep the map fixed, and move each sprite relative to the map, (if it's a movable sprite). It just doesn't make much sense to move everything in the world whenever your character moves around in the world.

If you want to render your world with your character always at the center, that's perfectly fine. The best thing to do is move the camera. This also allows you to zoom your camera in/out, rotate the camera, etc. with very little hassle in keeping track of all the objects in the world.

Be careful with your usage of the word "viewport". It means a very specific thing in OpenGL. (ie, look at the function glViewport). If your book uses it differently, that's fine. I'm just pointing this out because it's not 100% clear to me what you mean by it.