In the seventeenth video of the “Building a Game Development Framework” series, I implement a sophisticated Layering System and a new architectural concept called Game Maps. These updates provide 3D-like depth in a 2D game, enabling objects to be rendered on top of one another and moved across different visual planes.
I go from managing sprites directly in the Screen class to using a GameMap.
- Centralized Logic:
SimpleScreenis moved into theBaseScreen, and the logic for storing and updating sprites is delegated to theGameMap. - Custom Iterators: To handle complex updates (like removing an object from one layer and adding it to another in the same frame), the creator implements a custom
Iterator. This prevents “Concurrent Modification Exceptions” when the game tries to update the list of objects while it is still drawing them.
Entities now possess a layer property (an integer), allowing the framework to sort them from back to front.
- Rendering Order: The
GameMaprenders objects starting from layer 0 upward. Objects in higher layers are naturally drawn on top of those in lower layers. - Collision by Layer: To optimize performance and enable complex interactions, collision detection is updated to only check objects that are currently in the same layer.
Building on the previous “Mouse Drag” system, I add the ability to physically “lift” an object to a higher layer when it is grabbed.
- Vertical Transitions: When a user clicks a chip (like in Checkers), the movement class automatically increments its layer. This visually pulls the piece “up” toward the camera.
- Reversion on Collision: If a user tries to “drop” a piece into a lower layer where another object already exists, the framework detects the collision, reverses the layer change, and prevents the drop.
With multiple layers and overlapping sprites, a major technical hurdle is ensuring that a single click doesn’t trigger multiple objects simultaneously.
- The Lock System: The creator introduces an
InputLocksobject. When an actor is grabbed, it “locks” the mouse input to itself. Even if the user drags that actor over another one, the second actor ignores all input because it doesn’t hold the lock. - Two-Step Clearing: Unlocking is handled as a two-step process to ensure that a “release” click doesn’t accidentally trigger a different object on the frame immediately following the drop.
I show these features using red and black checker chips on a board:
- Stacking: Pieces can now be moved over one another without colliding if they are at different heights (layers).
- Layer Toggling: When a piece is clicked, it visually pops to the top layer. When released, it settles back down into the base layer.
- Drop Logic: You can successfully drag a piece over another, but you cannot “drop” it unless the square underneath is empty.
By the end of this video, the framework supports complex 2D depth, allowing for board games, top-down RPGs with multi-level environments, or UI systems with overlapping windows.