Everyone, First of all, thanks to Tobias Leech for so quickly answering my previous question on alpha values.
Now, I'm trying to understand movement. I managed to hack together a simple, choppy, "movement by teleportation" app in which one can use ASDW to move a rectangle around in the screen. However, inspired by the Pong code in the SDL manual, I'm trying to recreate this properly by using motion handlers. The resulting code is at http://pastebin.com/mVHANk7T The strange thing about it is that movement works just fine, but only up and to the left (ie via A and W) not to the right or down (ie via D and S). I'm at a bit of a loss as to what's going on...why would a negative x-velocity and positive y-velocity be fine, but not a positive x-velocity or a negative y-velocity? I know that the correct velocity values are being set (by de-commenting the debugging print statement and running the code), so it's not an issue of the wrong velocity values being set... Is there something obvious that I'm missing here? Thank you for your time, Jack