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+# FAQ
+
+### How to run it?
+
+There's no GUI. Find a directory with Minecraft Anvil files (.mca).
+Copy a Minecraft "terrain.png" into that directory (do a google
+image search). Run from that directory.
+
+### How accurate is this as a Minecraft viewer?
+
+Not very. Many Minecraft blocks are not handled correctly:
+
+*         No redstone, rails, or other "flat" blocks
+*         No signs, doors, fences, carpets, or other complicated geometry
+*         Stairs are turned into ramps
+*         Upper slabs turn into lower slabs
+*         Wood types only for blocks, not stairs, slabs, etc
+*         Colored glass becomes regular glass
+*         Glass panes become glass blocks
+*         Water is opaque
+*         Water level is incorrect
+*         No biome coloration
+*         Cactus is not shrunk, shows holes
+*         Chests are not shrunk
+*         Double-chests draw as two chests
+*         Pumpkins etc. are not rotated properly
+*         Torches are drawn hackily, do not attach to walls
+*         Incorrect textures for blocks that postdate terrain.png
+*         Transparent textures have black fringes due to non-premultiplied-alpha
+*         Skylight and block light are combined in a single value
+*         Only blocks at y=1..255 are shown (not y=0)
+*         If a 32x32x256 "quad-chunk" needs more than 800K quads, isn't handled (very unlikely)
+
+Some of these are due to engine limitations, and some of
+these are because I didn't make the effort since my
+goal was to make a demo for stb_voxel_render.h, not
+to make a proper Minecraft viewer.
+
+
+### Could this be turned into a proper Minecraft viewer?
+
+Yes and no. Yes, you could do it, but no, it wouldn't
+really resemble this code that much anymore.
+
+You could certainly use this engine to
+render the parts of Minecraft it works for, but many
+of the things it doesn't handle it can't handle at all
+(stairs, water, fences, carpets, etc) because it uses
+low-precision coordinates to store voxel data.
+
+You would have to render all of the stuff it doesn't
+handle through another rendering path. In a game (not
+a viewer) you would need such a path for movable entities
+like doors and carts anyway, so possibly handling other
+things that way wouldn't be so bad.
+
+Rails, ladders, and redstone lines could be implemented by
+using tex2 to overlay those effects, but you can't rotate
+tex1 and tex2 independently, so there may be cases where
+the underlying texture needs a different rotation from the
+overlaid texture, which would require separate rendering.
+Handling redstone's brightness being different from underlying
+block's brightness would require separate rendering.
+
+You can use the face-color effect to do biome coloration,
+but the change won't be smooth the way it is in Minecraft.
+
+
+### Why isn't building the mesh data faster?
+
+Partly because converting from minecraft data is expensive.
+
+Here is the approximate breakdown of an older version
+of this executable and lib that did the building single-threaded.
+
+*       25%   loading & parsing minecraft files (4/5ths of this is my crappy zlib)
+*       18%   converting from minecraft blockids & lighting to stb blockids & lighting
+*       10%   reordering from data[z][y]\[x] (minecraft-style) to data[y][x]\[z] (stb-style)
+*       40%   building mesh data
+*        7%   uploading mesh data to OpenGL
+
+I did do significant optimizations after the above, so the
+final breakdown is different, but it should give you some
+sense of the costs.
+