Mapgen v6: Fix mudflow iteration and iterate twice (#8795)

In MapgenV6::flowMud(), the previous implementation of coordinate
inversion caused the 2 inverted mudflow iterations (out of the 3
iterations) to not loop over the area, so only 1 non-inverted
iteration occurred.

Fix this bug but only iterate mudflow twice, as mapgen v6 has only
had 1 iteration for many years. There is now a good balance of 1
non-inverted iteration and 1 inverted iteration.

diff --git a/src/mapgen/mapgen_v6.cpp b/src/mapgen/mapgen_v6.cpp
index ae87b094dd4fc299c2d568fea3b26199b44d643c..28ca8faa2c9bed345bff2801f79e6b601058f420 100644 (file)
--- a/src/mapgen/mapgen_v6.cpp
+++ b/src/mapgen/mapgen_v6.cpp
@@ -773,22 +773,22 @@ void MapgenV6::addMud()
 
 void MapgenV6::flowMud(s16 &mudflow_minpos, s16 &mudflow_maxpos)
 {
-       // 340ms @cs=8
-       //TimeTaker timer1("flow mud");
-
-       // Iterate a few times
-       for (s16 k = 0; k < 3; k++) {
+       // Iterate twice
+       for (s16 k = 0; k < 2; k++) {
                for (s16 z = mudflow_minpos; z <= mudflow_maxpos; z++)
                for (s16 x = mudflow_minpos; x <= mudflow_maxpos; x++) {
-                       // Invert coordinates every 2nd iteration
-                       if (k % 2 == 0) {
-                               x = mudflow_maxpos - (x - mudflow_minpos);
-                               z = mudflow_maxpos - (z - mudflow_minpos);
+                       // Node column position
+                       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 {
+                               p2d = v2s16(node_min.X, node_min.Z) + v2s16(x, z);
                        }
 
-                       // Node position in 2d
-                       v2s16 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;