Inject Code Into Multiple Game Classes

Code Injection via Class Transformation

SpASM enables injecting custom code into game classes during loading. This allows you to hook into game behavior, add new functionality, or modify existing methods across many classes at once.

Injection Workflow

1. Identify injection points in your target classes — specific methods or locations where your code should run. Use bytecode inspection to find suitable spots.

2. Generate bytecode for your injected code using bytecode manipulation tools. Your injected code must be valid JVM bytecode that matches the expected stack state at the injection point.

3. Insert bytecode at the correct location within the target method. Common approaches include prepending code at method start, appending before returns, or inserting at specific instructions.

4. Manage stack and local variables carefully to avoid corrupting the method's execution state. Injected code must preserve stack integrity.

5. Test thoroughly with different game scenarios. Injected code runs early in the loading process, so errors may cause cascading failures.

6. Consider performance impact — transformations on frequently-called methods can affect game performance. Optimize your injected code accordingly.