In earlier versions of Java Edition, the heightmap debug renderer worked just fine. However, in modern versions, there is a noticeable decrease in performance whenever the debug renderer is enabled. I thought this was odd, so I decided to take a look at the source code. While I was reviewing the code, I noticed that there are multiple programming errors that are creating performance bottlenecks. These issues include redundant level/chunk calls, ignored frustum culling, and attempting to render an excessive amount of gizmos per frame.
To reproduce the issue, start up the game and log in to a server/singleplayer world. When you turn on the heightmap debug renderer in the Debug Options menu, there will be a lot of lag.
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Here are the screenshots. Please be advised that the screenshot for 1.21.8 is from before the debug properties were added. During this time, you had to use modifications to enable the heightmap debug renderer. This is the last version where it worked properly. I did not add any code which modified the heightmap debug renderer itself; it only added a way to enable it.
As for the latest snapshot, the performance issues were actually even worse when I was in the process of getting the screenshot you needed. You can see this for yourself in the FPS chart.
And to be honest, any issues with the renderers are worth fixing. The point of the renderers and other tools is to assist with debugging. If the debug features don’t work properly, that defeats the purpose of them being in the game.
I’ve finally gotten around to testing myself, and my performance is significantly better in 26.3 Snapshot 9 than in 26.2 - and this is in spite of MC-310154 degrading my performance when using OpenGL.
This being the case, and your experiences in 1.21.8 being invalid since the renderer was not a supported feature at that time, I’m not particularly confident that Mojang will accept this report; but since I can find no precedent to the contrary, but I will mark it as Plausible and see how they feel about tracking these sorts of issues.
Thank you for your report!
After consideration, the issue is being closed as Invalid.
This report does not describe a bug.
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Please upload 3 screenshots with both the heightmap renderer and FPS chart (F3 + 2) enabled, and with the game version and system specs showing in the debug overlay. Upload 1 screenshot each for whichever version of the game the renderer worked best on; for the latest release (currently 26.2); and for the latest snapshot (currently 26.3 Snapshot 8). Try to remove as many variables as possible by using the same world and taking the screenshots in a realistic situation (e.g. looking down a hillside at a village and ocean), and keep your video settings as similar as possible to mitigate the effects of any other performance improvements or regressions.
The intention with these screenshots should be to demonstrate that this issue is worth fixing. Since the game states that debug options “may slow down your computer”, the standard of an issue being worth fixing is higher than for other performance issues. Code analysis would also be helpful but is not a requirement- I know from experience that fetching good screenshots from multiple versions of the game can be a bit of a hassle.