Welcome back! In this tutorial, we are going to look at the solution to the intermediate 25 homework, which is to implement pattern matching using type information. This solution is a bit involved, but I will guide you through the process step by step.
Contents
Implementation Details
First, let’s go through the changes I made to the existing code. The main addition is the creation of a pattern matching listener, which is responsible for handling collisions between different types of color traits. This listener uses an unordered map to store the combinations of color traits and their corresponding handlers.
Additionally, I added an action system to separate the creation of effects from their execution. This allows us to add various effects, such as destruction and splitting, without impacting the simulation in real-time.
Pattern Matching Listener
To implement the pattern matching functionality, I created a PatternMatchingListener class that inherits from b2ContactListener and adds the necessary logic to handle collisions. The listener contains an unordered map, where the key is a pair of pointers to type_info, representing the color traits involved in the collision. The value is a function pointer to the handler for that specific combination.
The listener provides an interface to add patterns using the AddPattern function. This function takes the two color traits and the corresponding handler function and adds them to the unordered map.
During the collision handling process, the listener checks if the colliding bodies have dynamic types. If they do, it retrieves the color traits and looks for a matching pattern in the unordered map. If a pattern is found, it calls the corresponding handler function.
Action System
The action system allows us to create and execute actions after the simulation step. An action is a class that inherits from a base Action class and implements a Do function. This function takes a reference to the container of boxes and the Box2D world and performs the desired action on the boxes.
In the game loop, after stepping the world, the Action system iterates over the list of actions and executes them. This separation of creation and execution ensures that the actions are performed after the simulation step.
Splitting and Tagging Effects
To demonstrate the use of the action system, I added two effects: splitting and tagging. The splitting effect divides a box into four smaller boxes, while the tagging effect changes the color trait of a box to match the color trait of another box.
To trigger these effects, I added keypress handling. Pressing the space key triggers the splitting effect, and pressing the T key triggers the tagging effect. These effects will be executed in the action system after the simulation step.
Conclusion
In this tutorial, we covered the solution to the intermediate 25 homework, which involved implementing pattern matching using type information. We also introduced an action system to separate the creation and execution of effects in the simulation. This allowed us to add various effects without impacting the real-time simulation.
I hope you enjoyed this tutorial and found it helpful. Stay tuned for more advanced C++ game programming tutorials
