Happy Glass is a fun and funny puzzle game that requires a player to use physics and deductive reasoning skills to fill glass containers with water. Many containers in the game are empty and unhappy. The player follows various rules through three modes (Precise, Don't Spill and Flippy Glass) to cheer up each glass.
In Precise mode, the player must guesstimate the exact amount of water needed from a tap to fill a container with nothing more than the size of the container against a graph sheet background as a guide. In Don't Spill mode, they must remove a variety of block shapes from under a container without spilling the water in it. In Flippy Glass mode, they must flip a glass successfully into a prearranged spot under a tap using a line that they draw between the glass and the space.
Any time that the player makes the glass container happy, they receive coins that they can use to purchase different water colors and faces. With the latter, they change the color of the glass as well as the facial expressions.