First, greetings and salutations. I'm a new poster here, though I've browsed the forums and articles many times in the past, and have come to ask for assistance with my current project. Any help, even the tiniest of nudges in the right direction, will be most appreciated.

I am currently, as the title suggests, working on a Shmup style game, specifically a Vertically Scrolling Arcade Space Shooter. The game is written in Java, using the wonderful Libgdx framework. I have the core mechanics working, namely the enemy movement, power-ups, etc. I can have endless random waves of enemies to shoot but I'm completely at a loss when it comes to creating actual levels that control when and where the enemies should spawn. A bit of research has led me to believe that there are two main ideas when it comes to this. First, using a spatial map editor system to place enemies that are activated when the camera/character draws near. Second, using LUA or XML files to script enemy spawning based on time. Either of the options would work for me but, sadly, I'm not even sure where to begin to implement either one.

My question is, what would be a good method for creating levels/waves for a game such as this?

Again, any help or advice is very much appreciated. If more information is required on my part, please, ask away and I'll do my best to answer any questions.

<Level>
  <Spawn Scroll="10" Position="0, 0" Enemy="Airplane" Pattern="StraightAcross"/>
  <Spawn Scroll="10" Position="10, 0" Enemy="Boat" Pattern="Stationary"/>
  <Spawn Scroll="15" Position="0, 0" Enemy="Airplane" Pattern="Loop01"/>
</Level>

void SpawnEnemies(int NewScrollPos)
{
  while ((NextSpawn < Spawns.Length()) && (Spawns[NextSpawn].Scroll <= NewScrollPos))
  {
    auto& itemToSpawn = Spawn[NextSpawn];
    SpawnEnemy(itemToSpawn.Enemy, itemToSpawn.Position, itemToSpawn.Pattern);
    ++NextSpawn;
  }
}

Edit: Beaten out by SmkViper when I had to run an errand. Blast!

Thank you all for the quick responses! You've been very helpful and after some consideration, I've decided to go with an editor instead of setting up timing in a text/lua/xml file. I feel that, despite the extra work involved upfront, an actual level editor would allow me to design the levels/waves much more efficiently than scripting everything out.

My question now is this; Could the Tiled map editor be used in this situation or is it not a good solution? I could create my own map editor but I believe, if I'm not completely off base here, that Tiled would be able to do what I need it to fairly effectively.

My question now is this; Could the Tiled map editor be used in this situation or is it not a good solution? I could create my own map editor but I believe, if I'm not completely off base here, that Tiled would be able to do what I need it to fairly effectively.

Tiled should be fine. You could define particular tile types as spawners pretty easily (even on an invisible [in your game] layer).

Personally though, I just prefer procedural level generation. It saves you a lot of headache and work in level editing, and you don't have to worry about importing and parsing the tiled map.

It's a bit of tweaking your algorithm, but depending on how long you plan your game to be, can be a lot less work in the end (Also, if you need to change the game balance, which is likely, you don't have to go back and re-edit all of the levels: you just tweak your procedural generation a bit).