Game Programming Patterns by Nystrom Robert

Author:Nystrom, Robert [Nystrom, Robert]
Language: eng
Format: epub
Tags: Non-fiction, Game Programming, Software Architecture, Computers, Programming, Games
Publisher: Genever Benning
Published: 2014-11-01T22:00:00+00:00

Do you see all of those “remembers” and “recalls”? Each “remember” corresponds to a push, and the “recalls” are pops. That means we can translate this to bytecode pretty easily. For example, the first line to get the wizard’s current health is:

LITERAL 0 GET_HEALTH

This bit of bytecode pushes the wizard’s health onto the stack. If we mechanically translate each line like that, we end up with a chunk of bytecode that evaluates our original expression. To give you a feel for how the instructions compose, I’ve done that below.

To show how the stack changes over time, we’ll walk through a sample execution where the wizard’s current stats are 45 health, 7 agility, and 11 wisdom. Next to each instruction is what the stack looks like after executing it and then a little comment explaining the instruction’s purpose:

LITERAL 0 [0] # Wizard index LITERAL 0 [0, 0] # Wizard index GET_HEALTH [0, 45] # getHealth() LITERAL 0 [0, 45, 0] # Wizard index GET_AGILITY [0, 45, 7] # getAgility() LITERAL 0 [0, 45, 7, 0] # Wizard index GET_WISDOM [0, 45, 7, 11] # getWisdom() ADD [0, 45, 18] # Add agility and wisdom LITERAL 2 [0, 45, 18, 2] # Divisor DIVIDE [0, 45, 9] # Average agility and wisdom ADD [0, 54] # Add average to current health SET_HEALTH [] # Set health to result

If you watch the stack at each step, you can see how data flows through it almost like magic. We push 0 for the wizard index at the beginning, and it just hangs around at the bottom of the stack until we finally need it for the last SET_HEALTH at the end.

Maybe my threshold for “magic” is a little too low here.

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