FPS halved when using minimal vs vanilla

[FluffyDiscord]

Hey there, I have RTX 4090 with Ryzen 9800X3D. Basically top line hardware.

Weird thing is, that when I set Smooth Lightning quality even to Minimal, my FPS halves, so that would be from 165 to around 80fps (using High Fps Support mod). The difference between minimal and ultra preset it another ~30fps down, so ultra gives me 50fps.

The FPS drop seem to be too harsh, even when you have the minimal preset. The Smooth Lightning literally tanks performance.

The worst thing is that neither my GPU not CPU is even utilized at all. GPU sitting at comfy 6% and my CPU at 8%. The multithreading config option does nothing for me.

[RexBerry]

Single-threaded CPU seems to be a bottleneck with Terraria's render code (especially if you have a lot of mods installed), so I'm not surprised the CPU and GPU aren't being used much. I would try lowering the in-game resolution to 1920x1080 (or 1920x1200).

[FluffyDiscord]

What is the "thread count" config option for then? Also the tooltip for enabling smooth lightning says that it uses GPU, not CPU. Misleading then?

[RexBerry]

Thread count is for processing the light map (blurring, light color tone mapping) and for the fancy lighting engine. The main performance issue with smooth lighting is that every time it renders tiles, walls, and liquids, it does it 2 times (3 times if improved glow effect accuracy is enabled, like in the ultra preset) in order to support glow masks. The rendering code in Terraria is an unorganized mess and mods are allowed to do basically anything when drawing tiles, so there is no way to draw glow masks separately other than to draw tiles multiple times at different brightness levels. The rendering system in Terraria prioritizes flexibility over efficiency, so single-threaded CPU performance is important.

Yes, I suppose I should update the tooltip. Before v0.8.0, there was no true glow mask support, so smooth lighting did not change how many times tiles were rendered.

[FluffyDiscord]

Thanks for clarifying that. I have not looked at your code, but do you think you could perhaps cache calculated light and update it for example every second frame and approximating between if possible and use maybe half resolution, eg. skipping every second or third pixel and approximating between? I think you could have this on lower presets or as standalone config options. I would say this could boost FPS drastically while still being an improvement from vanilla. What do you think?

[RexBerry]

The main performance issue is drawing the tiles multiple times. Applying/compositing the lighting onto the tiles is more GPU-dependent, and processing the light map is multithreaded. Terraria already computes lighting and renders tiles/wall/liquids only once every four frames, and the work is spread across multiple frames so different things are updated each frame. I don't know how/if High FPS Support changes this, but I'd guess it doesn't for performance reasons and because the game runs at 60 ticks per second regardless.