Avoid User-defined Block-flags (to avoid transparency-related issues)

[KokeCacao]

Proposal: We should avoid user-defined export const OPAQUE_BLOCKS, export const TRANSLUCENT_BLOCKS, export const NON_SELF_CULLING, or at least have a way to automatically generate them.

Reason: minecraft:glass is rendered incorrectly when a proper fix on transparency is installed, but the user incorrectly missed glass in TRANSLUCENT_BLOCKS, causing the correct algorithm to misbehave.

• Since many fixes to transparency-related issues, we no longer need if (texColor.a < 0.5) discard in the shader. This will ensure that a semi-transparent object is rendered correctly.
• Not defining minecraft:glass as TRANSLUCENT_BLOCKS is fine with if (texColor.a < 0.5) discard since, unlike stained_glass, glass has binary transparency.
• With a proper transparency fix, we render based on sorted geometry and depth buffer. Not defining minecraft:glass as TRANSLUCENT_BLOCKS will mess up sorting.
• To prevent this issue from happening, and with Mojang keep introducing new blocks, we need an automatic way to assign these block flags.

[jacobsjo]

Since many fixes to transparency-related issues, we no longer need if (texColor.a < 0.5) discard in the shader. This will ensure that a semi-transparent object is rendered correctly.

Why? This case is needed for all the blocks with textures with binary transparency. Glass is by far not the only texture with binary transparency. Leaves, Crops, Doors, just to name a few. We can't treat them all as semi-transparent unless we have proper depth sorting (which is a very hard problem, your PR isn't the solution as discussed)

edit to clarify: I'm not sure where the 0.5 comes from. The line we have is if(texColor.a < 0.01) discard; to only discard pixels that are completely transparent.

Not defining minecraft:glass as TRANSLUCENT_BLOCKS is fine with if (texColor.a < 0.5) discard since, unlike stained_glass, glass has binary transparency.

Glass (and all other blocks with binary transparency) shouldn't have the semi_transparent block flag.

With a proper transparency fix, we render based on sorted geometry and depth buffer. Not defining minecraft:glass as TRANSLUCENT_BLOCKS will mess up sorting.

How would sorting the semi transparent meshes mess up rendering of the solid meshes?

To prevent this issue from happening, and with Mojang keep introducing new blocks, we need an automatic way to assign these block flags.

How would you propose to assign the flags? It would be great if there was an easy way to do that. But the whole point of the flags is that we haven't found one, so they need to be provided by the library user instead.

[KokeCacao]

Why? This case is needed for all the blocks with textures with binary transparency. Glass is by far not the only texture with binary transparency. Leaves, Crops, Doors, just to name a few. We can't treat them all as semi-transparent unless we have proper depth sorting (which is a very hard problem, your PR isn't the solution as discussed)

We should have depth sorting. Would 224ms rendering for (144x82x173) mostly glass, or 5ms for (3x3x3) glass planes, 1ms for (41x15x27) normal building, okay? I'm not quite sure what's the standard for online rendering.

edit to clarify: I'm not sure where the 0.5 comes from.

Sorry, that was my typo.

Glass (and all other blocks with binary transparency) shouldn't have the semi_transparent block flag.

When sorting is implemented (not currently), they should be sorted as translucent blocks to prevent incorrect occlusion under LOD>0

How would sorting the semi transparent meshes mess up rendering of the solid meshes?

It would not. Not sure whether I interpreted correctly. If you ask "Why would not sorting glass mess up rendering of other solid meshes", then the answer is: we might occasionally run into rendering glass first and it updates the depth buffer therefore failed to render solid behind it.

How would you propose to assign the flags?

Good question! I am thinking about checking for opacity in the atlas.png. If the averaged opacity for a block / quad is below 1, we make it TRANSLUCENT_BLOCKS, otherwise a OPAQUE_BLOCKS. Not sure whether it covered other edge cases. For NON_SELF_CULLING, I have no idea. I can't think of any examples other than leaves

[KokeCacao]

Okay, I have implemented a version that automatically checks for opaque and transparent. opaque is for culling and transparent is for sorting Quads. Some definition:

cube: if any variant of a block contains a parent that starts with minecraft:cube_, then the block is cube.
transparent: if all pixels of all variant textures of a block have an average alpha of 255, then it is NOT transparent, otherwise transparent.
opaque: cube and NOT transparent blocks.

Note that although transparent can be defined at variant level (so that double slabs can be opaque for culling), and transparent can be defined at Quad level, defining them at block level can improve cache hit to reduce CPU time.

Of course, user-specified parameters in BlockFlags.ts will override those calculations.

Here are some examples of cube for us to check if they align with our expectations:

minecraft:red_carpet: NO.
minecraft:oak_trapdoor: NO.
minecraft:red_stained_glass: YES.
minecraft:diorite_wall: NO.
minecraft:soul_lantern: NO.
minecraft:smooth_stone_slab: NO.
minecraft:end_rod: NO.
minecraft:lightning_rod: NO.
minecraft:smooth_quartz_slab: NO.
minecraft:iron_trapdoor: NO.
minecraft:yellow_wool: YES.
minecraft:red_concrete: YES.
minecraft:stone_slab: NO.
minecraft:stone_stairs: NO.
minecraft:yellow_concrete: YES.
minecraft:stone: YES.
minecraft:smooth_quartz: YES.
minecraft:blue_concrete: YES.
minecraft:light_gray_wool: YES.
minecraft:smooth_quartz_stairs: NO.
minecraft:black_concrete: YES.
minecraft:stone_button: NO.
minecraft:gray_concrete: YES.
minecraft:blackstone_wall: NO.
minecraft:polished_blackstone_slab: NO.
minecraft:white_carpet: NO.
minecraft:orange_terracotta: YES.
minecraft:red_sandstone: YES.

Here are some examples of transparent for us to check if they align with our expectations:

minecraft:red_carpet: Non-Transparent
minecraft:oak_trapdoor: Transparent
minecraft:red_stained_glass: Transparent
minecraft:diorite_wall: Non-Transparent
minecraft:soul_lantern: Transparent
minecraft:smooth_stone_slab: Non-Transparent
minecraft:end_rod: Transparent
minecraft:lightning_rod: Transparent
minecraft:smooth_quartz_slab: Non-Transparent
minecraft:iron_trapdoor: Transparent
minecraft:yellow_wool: Non-Transparent
minecraft:red_concrete: Non-Transparent
minecraft:stone_slab: Non-Transparent
minecraft:stone_stairs: Non-Transparent
minecraft:yellow_concrete: Non-Transparent
minecraft:stone: Non-Transparent
minecraft:smooth_quartz: Non-Transparent
minecraft:blue_concrete: Non-Transparent
minecraft:light_gray_wool: Non-Transparent
minecraft:smooth_quartz_stairs: Non-Transparent
minecraft:black_concrete: Non-Transparent
minecraft:stone_button: Non-Transparent
minecraft:gray_concrete: Non-Transparent
minecraft:blackstone_wall: Non-Transparent
minecraft:polished_blackstone_slab: Non-Transparent
minecraft:white_carpet: Non-Transparent
minecraft:orange_terracotta: Non-Transparent
minecraft:red_sandstone: Non-Transparent

IMPORTANT NOTE: minecraft:glass under the above definition is transparent and NOT opaque. Since this relies on sorting, I will NOT submit a PR before sorting is merged. But feel free to discuss if there is any error.