HD mode requires is a Pro License. Feature set:

• HighDPI text.
• Texture Atlas auto-discovery (given a naming convention, we swap out sprites on your behalf based on its original file path you have it in code). We handle all the texture caching/perf stuff behind the scenes.
• Ability to remove the letter box so you can render “edge to edge” (eg: ultrawide displays).
• Input coordinate mapping normalized to 720p logical resolution.

Basically we handle all the bullshit related to different resolutions so you can focus on building your game.

PS: All license tiers of DragonRuby can be used for commercial purposes, royalty free.