error doing image collision detection with _MemGet

[Herve]

Wow man, amazing work! Redefining the characters must have taken you a long time — I’m impressed!

My Linux setup doesn’t recognize the _button instruction to read the keyboard, so I couldn’t move the player or make them shoot.
Everything else works well: rendering, robot movement, and collision detection are fine.

To gauge performance I added an FPS counter. All tests were done with the default size 3 for the player and robots. I also varied the resolution to see the performance impact (the higher the resolution, the fewer collisions). Results:

• 127 robots and 0 large robots: 38 FPS at 640×480.
  
• 42 FPS at 1024×768.
  
• Lowering to 320×240, it’s impossible to run with 127 robots — the initial placement algorithm loops because it can’t find non-colliding spots for all robots; at that resolution a placement of 100 robots succeeds and gives 40 FPS.
  
• With 0 robots and 100 large robots, performance drops — at 1024×768 we fall to 12 FPS.
  

Finally, to confirm performance depended on the pixel-overlap detection technique, I disabled it and kept only bounding-box detection: at 1024×768 with 127 robots we get 47 FPS, and with 127 large robots 20 FPS. Pixel-perfect detection has a significant cost. It’s fun to dig into, but if your goal is a game with many sprites you should prefer other, more performant techniques.