My ceiling looks dirty – in patches. I built a palace from quartz slabs expecting clean, white walls and ceiling. The walls look good, but the ceiling has patterns of deep shading depending on what's built above the slabs, not what's lighting them from below.
In fact, the lighting below these slabs has very little effect, as if the light must pass through the slab to the top before it can brighten the near face on the underside.
The slab ceiling is at the upper-half of its block level (so the underside is mid-block). The underside seems to be getting its lighting data from the upper side. It should be getting its light data from beneath (i.e. The illumination for an exposed slab top or bottom face should be whatever impinges upon the same face of the full block at its coordinates).
I have done some advanced searching here to find any earlier reports of this lighting bug, but have found none. I found other lighting bugs, but not this one. If you think you see a duplicate, then please PM me before dismissing my report (I'll happily admit duplication if it really is the case).
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If I place a dirt block beneath the ceiling, then a ceiling tile turns completely black (is not rendered), and there's a half-block of space between the not-rendered ceiling slab and the dirt block. When I remove the dirt block, the underside of the ceiling slab resumes its too-dim illumination.
Also, if I attach a torch to the dirt block, the light levels of the nearby ceiling slabs is not affected. Some of them remain quite dim even with a torch only half a block away.
What affects the slabs is what is built on top of them. Looking up at my ceiling, I can tell where the walls are on the 2nd floor. There's a distinct pattern of darkness where I've built above the slabs.
Can you provide some screen shots? I have seen similar glitches with ceiling lighting glitches, but i have not tested it with half slabs.
PS
Has this been tested in the 1.8 release?
I'm getting inconsistent behavior today. Sometimes adding a torch below the ceiling will light it up, and sometimes not. Maybe part of this problem is a finicky block-updating, not overall rendering. However, placing blocks above the ceiling always darkens the underside greatly, revealing the pattern of construction on the upper floor.
I took a screen shot and will try to upload it...
I added a few screenshots of how this lighting glitch affects different set ups. I won't be able to fix this, but these screen shots might help support this issue.
On 2014-09-06_16.14.47, the L shaped pattern is above the slabs and there is no light above them.
This is ongoing in 1.8.
I suspect that this behavior stems from slabs not being "opaque", and they're not opaque because they don't fill whole cubes. This leads to some unexpected "logic", in this case some solid stone objects become strangely translucent.
There really should be two factors at work. One is actual opacity, which should be a property of the material. The other is cube-filling, which is knowledge about the geometry of a block that can simplify some of the graphics rendering. Having looked at object rendering code, I don't envy the coder asked to add complexity.
Eventually, the material opacity should be separated from geometric cube-filling, and a block's cube-filling might even be expressed in each of three axes (or six faces) so that something like a slab or stairs would "fill" its cube in one or more directions but not crosswise (or it would occlude one or more faces while leaving others open). Such a scheme should also fix the black-gap bug where I should be able to see past a half-slab but the background blocks are not rendered (appear black).
Is this still an issue in the current Minecraft Snapshot 15w47c or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.
Does this persist if you place a block on the bottom of the darkened slabs then remove the block?