Fog Of War - XNA

Question

I'm creating my own top down 2D RTS game for personal educational purposes. Currently I really just copying Starcraft's design/ideas. I've decided I should probably implement Fog Of War too.

Let me just explain my expectations:

• Areas currently being explored (i.e. units are there) should be lit up.
• Areas previsouly explored (i.e. units were there) should be darker but show what things were there when your unit was there.
• Areas not explored (i.e. areas your units have never been to) should be completely black.
• There should be a gradient change from each type (e.g. explored to previously explored) [See Picture Below]

I don't really need to know how to actually do it, but I would like a nice kick.

Thanks!

Answer 1

You should add more information about how you are implementing the game, but here are a few sugestions:

• Keep a bitmap of the whole map, each time a new area is explored just flip the corresponding bits as they become visible. You can do the same for the revealed area.
• Enemy units are drawn only if they are in the revealed area. You'll need to keep a 'last seen' state for buildings in the FOW area.
• You don't need to update visibility every frame - depending on your maximum unit speed, 5 or 10fps should be quite enough.
• Assuming you are using square tiles, you'll just need 4 masks to get the results you need: one for a 'solid' (blacked out) tile, one 'elbow' and one 'corner' gradient, and one 'straight edge' gradient. You can get all others from these using rotations and different transparencies.

Hope that helps.