| dx, -dx |
| dy, -dy |

| get dy, W pressed | -dy, get dy
| get dy, S pressed |  dy
| get dx, A pressed | -dx, get dx
| get dx, D pressed |  dx


| loop | input, player, enemies, cull, re-loop
| input | poll
| player | get dx:max, get dy:max

|| loop

| update enemy | track player
| enemies, last enemy |
| enemies | update enemy, next enemy

| cull | remove dead enemies
| re-loop | loop

| get dy, W pressed | -dy, get dy
| get dy, S pressed |  dy
| get dx, A pressed | -dx, get dx
| get dx, D pressed |  dx


| loop | input, player, enemies, cull, re-loop
| input | poll
| player | get dx:max, get dy:max

| update enemy | track player
| enemies, last enemy |
| enemies | update enemy, next enemy

| cull | remove dead enemies
| re-loop | loop