HTML5 Canvas, 2nd Edition

Level Knobs

Even though we never show the level number to the game player, we are adjusting the difficulty every time a screen of rocks is cleared. We do this by increasing the level variable by 1 and then recalculating these values before the level begins. We refer to the variance in level difficulty as knobs, which refers to dials or switches. Here are the variables we will use for these knobs:

level+3

Number of rocks

levelRockMaxSpeedAdjust = level*.25;

Rock max speed

levelSaucerMax = 1+Math.floor(level/10);

Number of simultaneous saucers

levelSaucerOccurrenceRate = 10+3*level;

Percent chance a saucer will appear

levelSaucerSpeed = 1+.5*level;

Saucer speed

levelSaucerFireDelay = 120-10*level;

Delay between saucer missiles

levelSaucerFireRate = 20+3*level;

Percent chance a saucer will fire at the player

levelSaucerMissileSpeed = 1+.2*level;

Speed of saucer missiles