The stair block model renders a part of the texture it does not need to because it is not visible to the player unless if they are in spectator. This can have a minor performance impact because the GPU has to render part of a texture that does not need to be rendered.
How to reproduce
Go into spectator
Fly inside the top part of a stair block
This will work with any kind of stair. You have to look at it from the side the actual texture is on because of the way the game culls textures will you are inside of blocks. For tracking purposes this is reproducible on versions prior to 1.16.5. I have attached three pictures, one is while looking at the front of the step and the inside, the second one is what it looks like when you go inside of the step, and the third picture (named 1.8.10) was tested in 1.8.10 because the official Minecraft wiki states that the first version of the game to support spectator mode was 1.8. You can see the same issue is reproducible as well as a similar issue which is no longer present in newer versions of the game.
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Comments 7
I don't see any unnecessary faces – all are visible. Adding additional elements causes more faces to be drawn than were before.
@tryashtar, the additional elements have the faces inside of the stairs removed so the game only has to render the faces on the outside of the stair. So only model stitching time should be affected but that should be minimal. The thing that is wrong with the vanilla model is that the bottom element is the size of a half slab. That means below the elements which make up the upper part of the stair you can see the texture on that element. Even though the player can only see it if in spectator mode the game still draws that part of the texture while it can not be seen. The fix I made makes use of smaller elements with removed faces so that only the part exposed of the bottom is rendered.
Even if half of the texture is not seen, it's still only two triangles, both of which are visible. The vanilla stair model has two cubes and draws 22 triangles; your version has three cubes and draws 28 triangles
As an example, imagine this is a hopper seen from below. Even though the middle part of the texture isn't visible due to the funnel covering it, it's far more efficient to model this as one cube with two triangles than four cubes with eight
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I have made a fix for this bug. I have added additional elements to the block models that make it so the unnecessary faces do not render. The attached fix is a resource pack that works in 1.16.5 and the 1.17 snapshots. Just ignore the warning for 1.16.5 and below. I also give Mojang Studios full permissions to use the block models in the resource pack directly with or without modification.
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