Here is a sample project that I ported over to TwinCAT for running the classic snake game.  I used this as a sample to start out learning the ST language from ladder logic.  There is a 2D boolean array that stores pixels of the screen and another array set that has a shifting index for moving the snake between tiles.  The 'ball' or 'food' is a flashing bit that gets scanned and checked if the head of the 'snake' is in contact with it, then shifts down the tail array.  A random generator gets new x/y coordinates for the next 'ball' location, and is validated that it is not already part of the tail.

Some items of note:

• Uses a GVL 2-d array and the block checks bounds.  Dimensions on the array can be changed to whatever size as long as the visualization is updated
• Uses latching HMI buttons to set the direction in X or Y (-1 or +1 makes cursor go left or right)
• Setup variables initializes and resets all variables on bootup
• Option for autoscrolling where the 'snake' will continue in a loop around the border of the screen
• Option for enable crashes let me disable the end of game when debugging the initial programming
• Option for scan time on a slider permits the game speed to change
• High score and current score display

Other arcade games that I wrote at this time were something similar to the PONG/tennis game as well as the stacking block tower.  All of these were running on an HMI for a machine that was being built and I had the opportunity to use a joystick that was required for normal machine operation - much more fun than clicking on the visualization screen!