The Smooth tool uses a Gaussian blur to soften terrain. What sets it apart from other smoothing tools is that its algorithm maintains the same total block count within the brush stroke. Instead of adding or removing unnecessary mass, it attempts to spread blocks evenly across the chosen area based on the surroundings. This makes the brush more adaptive and precise, while also offering adjustable settings linked to this behaviour. The tool operates within the chosen area as defined by the brush settings, but remember that the blurring kernel also considers the surroundings of the selection.
The Smooth Strength controls the degree of terrain smoothing. By default, it's set to 2, which provides a pleasant smoothing effect. Lower strength is useful for refining areas with a lot of noise while preserving the overall shape. On the other hand, higher strengths blend and lump blocks together more drastically to achieve the smoothest shape possible.
The Modifiers, are settings related to smoothing behaviour. By default, the tool has a 100% Block Ratio in Stable mode. This means the tool will preserve all blocks (100%) and strive to keep things relatively unchanged during the smoothing process. If you increase the block ratio, it adds more mass, which is equivalent to the total number of selected blocks times the ratio. For instance, a 101% ratio means adding 1% more blocks, while a 99% ratio means removing 1% of blocks. For smaller areas, this allows precise tuning, while larger selections, due to their greater mass, will naturally grow or shrink more based on your settings. The Melt mode biases the removal of blocks and the Grow mode biases the addition of blocks to smooth the area. Combining these with the ratio allows for precise finetuning of the smoothing.
The "Fix edges" option, which is on by default, integrates the edge of the smoothed area with the existing terrain to avoid creating sharp contrasts. This makes the smoothed areas blend seamlessly with the rest of the terrain, preventing jagged edges.