Sometimes you want to build underwater with nothing but air between yourself and the water, even when the water is above you.
This idea makes that possible, by adding steam, an air-like block into which water cannot flow, and a boiler whose purpose is to make steam.
First, the boiler: This would be crafted from eight magma blocks, similar to the furnace recipe. Instead of using furnace fuel, it's only fuels would be magma blocks, magma cream, and lava. As long as there is fuel in the boiler, it will, every few game ticks, examine a random nearby block; if that examined block is water, the water is replaced by steam; if that examined block is steam, the steam is made hotter.
Next, the steam: It is very air-like, and doesn't affect movement or light or mob spawning, etc; also, like air in the nether, it does not injure the player. Steam does not respond to block updates, nor does it create or respond to scheduled updates, nor does it use a ticking tile entity.
Steam does respond to random block ticks: When a steam block is given a block tick, it looks at each of it's 6 neighboring blocks, and for each one, does the following:
If the neighboring block is air, and the steam's temperature is above zero, the steam decreases it's own temp by 1, and replaces the air by a copy of itself. If the steam's temp was equal to zero, the steam itself is replaced by air.
If the neighboring block is water, or a waterlogged block, or ice/snow/etc, the steam's temperature is decreased. If this would put it below zero, the steam replaces itself with water.
If neighboring block is steam, the difference in temperatures is taken, then divided by two (rounding down), and if the result is not zero, that amount of heat is moved from the hotter steam block to the cooler steam block.
Other blocks are ignored.
With this combination of rules, a boiler can fill a large but finite volume of space with steam, provided that it initially is full of air, and can keep the steam hot enough to prevent most of this from being cooled by water that it later comes into contact with.
TL;DR: You would first build an enclosed underwater structure, then remove most of the water (except the stuff near your boiler), then fill it with steam, then remove the enclosure; As long as you keep the boiler fueled, the steam will keep the water out.
Oh, and I was thinking that the temperature of steam would range from 0 to 15 inclusive, or perhaps 0 to 31 inclusive. Bigger numbers allow steam to spread further from the boiler, which makes it easier to conceal. Remember, the purpose of this idea is for aesthetic water manipulation, so forcing the player to have many boilers is less than ideal, even if the boilers themselves look nice, fuel automation might look a bit ugly.
Sometimes you want to build underwater with nothing but air between yourself and the water, even when the water is above you.
This idea makes that possible, by adding steam, an air-like block into which water cannot flow, and a boiler whose purpose is to make steam.
First, the boiler: This would be crafted from eight magma blocks, similar to the furnace recipe. Instead of using furnace fuel, it's only fuels would be magma blocks, magma cream, and lava. As long as there is fuel in the boiler, it will, every few game ticks, examine a random nearby block; if that examined block is water, the water is replaced by steam; if that examined block is steam, the steam is made hotter.
Next, the steam: It is very air-like, and doesn't affect movement or light or mob spawning, etc; also, like air in the nether, it does not injure the player. Steam does not respond to block updates, nor does it create or respond to scheduled updates, nor does it use a ticking tile entity.
Steam does respond to random block ticks: When a steam block is given a block tick, it looks at each of it's 6 neighboring blocks, and for each one, does the following:
With this combination of rules, a boiler can fill a large but finite volume of space with steam, provided that it initially is full of air, and can keep the steam hot enough to prevent most of this from being cooled by water that it later comes into contact with.
TL;DR: You would first build an enclosed underwater structure, then remove most of the water (except the stuff near your boiler), then fill it with steam, then remove the enclosure; As long as you keep the boiler fueled, the steam will keep the water out.
Oh, and I was thinking that the temperature of steam would range from 0 to 15 inclusive, or perhaps 0 to 31 inclusive. Bigger numbers allow steam to spread further from the boiler, which makes it easier to conceal. Remember, the purpose of this idea is for aesthetic water manipulation, so forcing the player to have many boilers is less than ideal, even if the boilers themselves look nice, fuel automation might look a bit ugly.