Canvas Games: Part I - HTML5 Canvas - page 689

Level Knobs

Even though we never show the level number to the game player, we are adjusting the diffi-
culty 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; levelRockMaxSpeedAdjust = level*.25;

Rock max speed

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

Number of simultaneous saucers

levelSaucerOccurrenceRate = 10+3*level; levelSaucerOccurrenceRate = 10+3*level;

Percent chance a saucer will appear

levelSaucerSpeed = 1+.5*level;

Saucer speed

levelSaucerFireDelay = 120-10*level; 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; levelSaucerMissileSpeed = 1+.2*level;

Speed of saucer missiles