Opacity is a property of blocks with a wide range of effects in Minecraft. Opacity's primary use is to tell the game engine if it has to draw behind the block; completely solid blocks completely obscure view behind them while transparent blocks do not. Transparency doesn't just apply only to clear solid blocks such as Quicksoil Glass, but also things like stairs and single slabs, which do not completely fill their space.
Opacity also affects how light generates through the Aether. Opaque blocks completely prevent light from going through them while transparent blocks diminish it by one level per block. This value can be overwritten, though.
|Solid Blocks||Cold Aercloud ( Blue • Golden • Green • Storm • Purple) • Aerogel • Quicksoil Glass • Holystone Furnace|
|Non-Solid Blocks||Present • Slider Labyrinth Totem • Quicksoil Glass Pane • Skyroot Bed • Skyroot Chest • Skyroot Door • Skyroot Fence Gate • Skyroot Fence • Skyroot Ladder • Skyroot Trap Door • Slabs • Stairs • Walls|
|Non-Solids||Aether Portal • Skyroot Sign • Ambrosium Torch|
|Plants||Berry Bush ( Stem) • Leaves • Sapling • Orange Tree • Purple Flower • Tall Aether Grass • White Rose|
Things affected by opacity
Not a lot of effects of opacity are obvious, and Minecraft doesn't have a "solid" property so opacity is tested for instead.
- Opaque blocks suffocate the player while transparent ones do not
- Hostile mobs cannot spawn on transparent blocks nor can they spawn inside completely opaque ones. They can however spawn inside non-solid transparent blocks, such as flowers.
- Chests cannot be opened if there are opaque blocks covering the top of them, transparent blocks do not count
- Torches cannot be attached to transparent blocks, this rule also applies to signs
- Water which is completely surrounded by water or solid blocks won't have currents. If one of the surrounding blocks are transparent, the water will flow down like a waterfall.
- Tree leaves can overwrite transparent blocks when they grow but not opaque blocks
- Further, leaves will change graphics depending on graphic settings (Fancy or Fast)
- Opacity affects door orientation when placed
- Beds can only successfully reset spawn point if the block at it's head is opaque
- Particles that are affected by gravity (e.g. slime particles) fall through transparent blocks
Transparency in this sense does not imply being able to see through it, but recent Minecraft versions have provisions against seeing through opaque blocks regardless of texture.
Transparent blocks can still reduce or block light:
- Glass does not reduce light passing through, so glass is treated as air
- Water is transparent but has a -2 modifier to light, on top of the normal -1 (for a total of -3)
- Leaves do not have any extra effects but they do diffuse sky light
- Slabs and stairs block light completely