Due to some unforeseen apartment maintenance, I didn't have as much time to invest today as I had hoped.
That said, I had made some progress anyway :)
I made a quad, slapped a tiling texture on it, and made it UV scroll from code. Presto, simple scrolling background. I might come back to this later and do something more fancy, e.g. add some more layers and do some simple parallax effect, but for now it's good enough.
I made another textured quad that I move around based on input, constrained within a movement area (defined via 2 corners I placed in the world). This is my player object. It fires a projectile based on input. My player needs a lot more work later on, but I have something moving, at least. One of many things to do is make this an animated thing, instead of a static texture. Apart from that, what I need to add will become apparent once I add in other features.
Yet another textured quad was made - this time it's a projectile. When spawned, it moves forward until it times out and is removed. I'll need to add collision detection here (once I have something to collide with), and I'll probably want to remove it if it exits the screen. I'll want to come back to this later on an use an object pool instead of instantiating and destroying objects all the time, but mainly for my own sake -- I doubt this project will run into performance issues given the simplicity of it all.
Before going further, I'll probably redo a few things -- shifting my camera from top-down to side-view, making the game window portrait instead of landscape (so it makes sense if I get it on a mobile device later on), and other small stuff like that.
Next will be an enemy that moves in some fashion and that you can defeat. Upon defeat, it will spawn some currency that the player can collect. Once that's up and running, a system for spawning the enemies in waves (first iteration probably just timed/formula based). Other than that, their behaviour is undefined at the moment. Maybe some firing back at the player. At some point later on there will also be an object pool for this (like with the projectiles).
Once I have a basic enemy that moves around, the plan is to deal with health somehow (instead of hit = death), both for the player and the enemies.
This will also mean I'll do some GUI/HUD stuff to keep track of currency, health, and other related bits and pieces.
After that I'll probably want to do something with the shop/upgrade system.
Past that, it's a bit fuzzy, but I'll have a clearer picture once I've started on the above.