blitToVManip: Check out-of-bounds using node position not index (#8127)

Previously, when using 'place on vmanip' to add a schematic to a
lua voxelmanip, if part of the schematic was outside the voxelmanip
volume, the outside part would often appear in a strange place
elsewhere inside the voxelmanip instead of being trimmed off.
This was due to the out-of-bounds check checking the index.

A position outside the voxelmanip can have an index that satisfies
'0 <= index <= voxelmanip volume', causing the node to be placed
at a strange position inside the voxelmanip.

Use 'vm->m_area.contains(pos)' instead.
Move index calculation to later in the code to optimise.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/mapgen/mg_schematic.cpp b/src/mapgen/mg_schematic.cpp
index ba619b2e0..36f1dd76b 100644
--- a/src/mapgen/mg_schematic.cpp
+++ b/src/mapgen/mg_schematic.cpp
@@ -137,8 +137,8 @@ void Schematic::blitToVManip(MMVManip *vm, v3s16 p, Rotation rot, bool force_pla
 		for (s16 z = 0; z != sz; z++) {
 			u32 i = z * i_step_z + y * ystride + i_start;
 			for (s16 x = 0; x != sx; x++, i += i_step_x) {
-				u32 vi = vm->m_area.index(p.X + x, y_map, p.Z + z);
-				if (!vm->m_area.contains(vi))
+				v3s16 pos(p.X + x, y_map, p.Z + z);
+				if (!vm->m_area.contains(pos))
 					continue;
 
 				if (schemdata[i].getContent() == CONTENT_IGNORE)
@@ -150,6 +150,7 @@ void Schematic::blitToVManip(MMVManip *vm, v3s16 p, Rotation rot, bool force_pla
 				if (placement_prob == MTSCHEM_PROB_NEVER)
 					continue;
 
+				u32 vi = vm->m_area.index(pos);
 				if (!force_place && !force_place_node) {
 					content_t c = vm->m_data[vi].getContent();
 					if (c != CONTENT_AIR && c != CONTENT_IGNORE)