Mapgen v6: Various mudflow code improvements and bugfixes (#8805)

Calculate 'i' inside 'y' loop to avoid 'i' and 'y' becoming
out of step due to the uses of 'continue'.
Simplify calculation of 'p2d' when coordinates are inverted.
Remove some unnecessary and unreliable 'index out of
voxelmanip' checks.
Move calculation of '&em' out of loops.
For 'Loop further down until not air' code, use y coordinate
to detect being out of voxelmanip, instead of checking index
which did not detect that.
Add and improve comments.
Indent the 'for (;; y--) {' loop.
Improve format and fix codestyle issues.

src/mapgen/mapgen_v6.cpp

@@ -538,7 +538,7 @@ void MapgenV6::makeChunk(BlockMakeData *data)
	updateHeightmap(node_min, node_max);

	const s16 max_spread_amount = MAP_BLOCKSIZE;
	// Limit dirt flow area by 1 because mud is flown into neighbors.
	// Limit dirt flow area by 1 because mud is flowed into neighbors
	s16 mudflow_minpos = -max_spread_amount + 1;
	s16 mudflow_maxpos = central_area_size.X + max_spread_amount - 2;

@@ -773,6 +773,14 @@ void MapgenV6::addMud()

void MapgenV6::flowMud(s16 &mudflow_minpos, s16 &mudflow_maxpos)
{
	const v3s16 &em = vm->m_area.getExtent();
	static const v3s16 dirs4[4] = {
		v3s16(0, 0, 1), // Back
		v3s16(1, 0, 0), // Right
		v3s16(0, 0, -1), // Front
		v3s16(-1, 0, 0), // Left
	};

	// Iterate twice
	for (s16 k = 0; k < 2; k++) {
		for (s16 z = mudflow_minpos; z <= mudflow_maxpos; z++)
@@ -781,120 +789,97 @@ void MapgenV6::flowMud(s16 &mudflow_minpos, s16 &mudflow_maxpos)
			v2s16 p2d;
			// Invert coordinates on second iteration to process columns in
			// opposite order, to avoid a directional bias.
			if (k == 1) {
				p2d = v2s16(node_min.X, node_min.Z) + v2s16(
					mudflow_maxpos - (x - mudflow_minpos),
					mudflow_maxpos - (z - mudflow_minpos));
			} else {
			if (k == 1)
				p2d = v2s16(node_max.X, node_max.Z) - v2s16(x, z);
			else
				p2d = v2s16(node_min.X, node_min.Z) + v2s16(x, z);
			}

			const v3s16 &em = vm->m_area.getExtent();
			u32 i = vm->m_area.index(p2d.X, node_max.Y, p2d.Y);
			s16 y = node_max.Y;

			while (y >= node_min.Y) {
				for (;; y--) {
					u32 i = vm->m_area.index(p2d.X, y, p2d.Y);
					MapNode *n = nullptr;

					// Find next mud node in mapchunk column
					for (; y >= node_min.Y; y--) {
						n = &vm->m_data[i];
						if (n->getContent() == c_dirt ||
								n->getContent() == c_dirt_with_grass ||
								n->getContent() == c_gravel)
							break;

			for (;; y--) {
				MapNode *n = NULL;
				// Find mud
				for (; y >= node_min.Y; y--) {
					n = &vm->m_data[i];
					if (n->getContent() == c_dirt ||
							n->getContent() == c_dirt_with_grass ||
							n->getContent() == c_gravel)
						VoxelArea::add_y(em, i, -1);
					}
					if (y < node_min.Y)
						// No mud found in mapchunk column, process the next column
						break;

					VoxelArea::add_y(em, i, -1);
				}

				// Stop if out of area
				//if(vmanip.m_area.contains(i) == false)
				if (y < node_min.Y)
					break;

				if (n->getContent() == c_dirt ||
						n->getContent() == c_dirt_with_grass) {
					// Make it exactly mud
					n->setContent(c_dirt);

					// Don't flow it if the stuff under it is not mud
					{
					if (n->getContent() == c_dirt || n->getContent() == c_dirt_with_grass) {
						// Convert dirt_with_grass to dirt
						n->setContent(c_dirt);
						// Don't flow mud if the stuff under it is not mud,
						// to leave at least 1 node of mud.
						u32 i2 = i;
						VoxelArea::add_y(em, i2, -1);
						// Cancel if out of area
						if (!vm->m_area.contains(i2))
							continue;
						MapNode *n2 = &vm->m_data[i2];
						if (n2->getContent() != c_dirt &&
								n2->getContent() != c_dirt_with_grass)
							// Find next mud node in column
							continue;
					}
				}

				static const v3s16 dirs4[4] = {
					v3s16(0, 0, 1), // back
					v3s16(1, 0, 0), // right
					v3s16(0, 0, -1), // front
					v3s16(-1, 0, 0), // left
				};

				// Check that upper is walkable. Cancel
				// dropping if upper keeps it in place.
				u32 i3 = i;
				VoxelArea::add_y(em, i3, 1);
				MapNode *n3 = NULL;

				if (vm->m_area.contains(i3)) {
					n3 = &vm->m_data[i3];
					// Check if node above is walkable. If so, cancel
					// flowing as if node above keeps it in place.
					u32 i3 = i;
					VoxelArea::add_y(em, i3, 1);
					MapNode *n3 = &vm->m_data[i3];
					if (ndef->get(*n3).walkable)
						// Find next mud node in column
						continue;
				}

				// Drop mud on side
				for (const v3s16 &dirp : dirs4) {
					u32 i2 = i;
					// Move to side
					VoxelArea::add_p(em, i2, dirp);
					// Fail if out of area
					if (!vm->m_area.contains(i2))
						continue;
					// Check that side is air
					MapNode *n2 = &vm->m_data[i2];
					if (ndef->get(*n2).walkable)
						continue;
					// Check that under side is air
					VoxelArea::add_y(em, i2, -1);
					if (!vm->m_area.contains(i2))
						continue;
					n2 = &vm->m_data[i2];
					if (ndef->get(*n2).walkable)
						continue;
					// Loop further down until not air
					bool dropped_to_unknown = false;
					do {
					// Drop mud on one side
					for (const v3s16 &dirp : dirs4) {
						u32 i2 = i;
						// Move to side
						VoxelArea::add_p(em, i2, dirp);
						// Check that side is air
						MapNode *n2 = &vm->m_data[i2];
						if (ndef->get(*n2).walkable)
							continue;

						// Check that under side is air
						VoxelArea::add_y(em, i2, -1);
						n2 = &vm->m_data[i2];
						// if out of known area
						if (!vm->m_area.contains(i2) ||
								n2->getContent() == CONTENT_IGNORE) {
							dropped_to_unknown = true;
							break;
						}
					} while (!ndef->get(*n2).walkable);
					// Loop one up so that we're in air
					VoxelArea::add_y(em, i2, 1);

					// Move mud to new place. Outside mapchunk remove
					// any decorations above removed or placed mud.
					if (!dropped_to_unknown)
						moveMud(i, i2, i3, p2d, em);
						if (ndef->get(*n2).walkable)
							continue;

					// Done
					break;
						// Loop further down until not air
						s16 y2 = y - 1; // y of i2
						bool dropped_to_unknown = false;
						do {
							y2--;
							VoxelArea::add_y(em, i2, -1);
							n2 = &vm->m_data[i2];
							// If out of area or in ungenerated world
							if (y2 < full_node_min.Y || n2->getContent() == CONTENT_IGNORE) {
								dropped_to_unknown = true;
								break;
							}
						} while (!ndef->get(*n2).walkable);

						if (!dropped_to_unknown) {
							// Move up one so that we're in air
							VoxelArea::add_y(em, i2, 1);
							// Move mud to new place, and if outside mapchunk remove
							// any decorations above removed or placed mud.
							moveMud(i, i2, i3, p2d, em);
						}
						// Done, find next mud node in column
						break;
					}
				}
			}
			}
		}
	}
}