Upon crossing a chunk border, the server heightmap, local difficulty and blending method are not displayed on the debug screen (F3) for 1 frame, causing apparent flickering

Upon entering a new chunk, the server heightmap, local difficulty, and blending method are not displayed on the debug screen (F3) for 1 frame, causing apparent flickering on the debug screen. This is not really an issue when in an area generated with new blending, but for areas with old blending the blending line is simply omitted for that frame, causing all lines below it to jump upwards, which is quite annoying if the player’s GUI scale is anything above 1 or 2.

To reproduce

1. Enable the debug screen (F3)

2. Enable chunk border display (F3+G)

3. Cross a chunk border (you may need to be moving quickly, eg. flying with elytra, in order to reproduce)
   ❌ The SH and Local Difficulty lines show question marks for a single frame (may be intended, but noticeable), and if the area uses old blending, that line is omitted for a single frame, causing all lines below it to be pushed upwards by 1

Expected behavior

Either the data for the chunk the player is about to enter should be fetched from the server beforehand, or the blending line should be present for all chunks so that it can display “Blending: Old“, “Blending: New“ or “Blending: ??“. The latter approach probably makes more sense.

Recommended approach

This issue would be meaninglessly minor if the debug screen were used solely for debugging the game, but as of 1.21.8-rc1 it is still the only way for the player to access important in-game information such as the coordinates, biome, light level and local difficulty. Players shouldn’t have to contend with flickering in the HUD when just playing normally. It’s time to add a dedicated information HUD for everyday use; please consider reading my post on the Feedback Discord outlining this idea. Once this feature has been added this issue can be closed as Won’t Fix if desired, since leaving it unfixed will have only the tiniest gameplay impact.