worldedit-core/src/main/java/com/fastasyncworldedit/core/command/tool/brush/PopulateSchem.java

@@ -24,7 +24,8 @@ public record PopulateSchem(Mask mask, List<ClipboardHolder> clipboards, int rar
         CuboidRegion cuboid = new CuboidRegion(
                 editSession.getWorld(),
                 position.subtract(size1, size1, size1),
-                position.add(size1, size1, size1)
+                position.add(size1, size1, size1),
+                true
         );
         try {
             editSession.addSchems(cuboid, mask, clipboards, rarity, randomRotate);

worldedit-core/src/main/java/com/fastasyncworldedit/core/function/generator/SchemGen.java

@@ -7,6 +7,7 @@ import com.sk89q.worldedit.extent.clipboard.Clipboard;
 import com.sk89q.worldedit.function.mask.Mask;
 import com.sk89q.worldedit.math.transform.AffineTransform;
 import com.sk89q.worldedit.math.transform.Transform;
+import com.sk89q.worldedit.regions.Region;
 import com.sk89q.worldedit.session.ClipboardHolder;
 
 import java.util.List;
@@ -19,29 +20,60 @@ public class SchemGen implements Resource {
     private final List<ClipboardHolder> clipboards;
     private final boolean randomRotate;
     private final Mask mask;
+    private final Region region;
 
     private final MutableBlockVector3 mutable = new MutableBlockVector3();
 
+    /**
+     * @deprecated Use {@link SchemGen#SchemGen(Mask, Extent, List, boolean, Region)}
+     */
+    @Deprecated(forRemoval = true, since = "TODO")
     public SchemGen(Mask mask, Extent extent, List<ClipboardHolder> clipboards, boolean randomRotate) {
         this.mask = mask;
         this.extent = extent;
         this.clipboards = clipboards;
         this.randomRotate = randomRotate;
+        this.region = null;
+    }
+
+    /**
+     * New instance. Places a schematic on terrain at a given x,z when appropriate
+     *
+     * @since TODO
+     */
+    public SchemGen(Mask mask, Extent extent, List<ClipboardHolder> clipboards, boolean randomRotate, Region region) {
+        this.mask = mask;
+        this.extent = extent;
+        this.clipboards = clipboards;
+        this.randomRotate = randomRotate;
+        this.region = region;
+    }
+
+    private int getY(int x, int z) {
+        if (region == null) {
+            return extent.getNearestSurfaceTerrainBlock(
+                    x,
+                    z,
+                    mutable.y(),
+                    this.extent.getMinY(),
+                    this.extent.getMaxY(),
+                    Integer.MIN_VALUE,
+                    Integer.MAX_VALUE
+            );
+        } else {
+            int y = extent.getHighestTerrainBlock(x, z, region.getMinimumY(), region.getMaximumY(), mask);
+            if (y == region.getMinimumY() && !extent.getBlock(x, y, z).getMaterial().isMovementBlocker()) {
+                return Integer.MIN_VALUE;
+            }
+            return y;
+        }
     }
 
     @Override
     public boolean spawn(Random random, int x, int z) throws WorldEditException {
         mutable.mutX(x);
         mutable.mutZ(z);
-        int y = extent.getNearestSurfaceTerrainBlock(
-                x,
-                z,
-                mutable.y(),
-                this.extent.getMinY(),
-                this.extent.getMaxY(),
-                Integer.MIN_VALUE,
-                Integer.MAX_VALUE
-        );
+        int y = getY(x, z);
         if (y == Integer.MIN_VALUE || y == Integer.MAX_VALUE) {
             return false;
         }
@@ -54,7 +86,8 @@ public class SchemGen implements Resource {
         if (randomRotate) {
             holder.setTransform(new AffineTransform().rotateY(ThreadLocalRandom.current().nextInt(4) * 90));
         }
-        Clipboard clipboard = holder.getClipboard();
+        Clipboard clipboard = holder.getClipboards().size() == 1 ? holder.getClipboard() :
+                holder.getClipboards().get(ThreadLocalRandom.current().nextInt(clipboards.size()));
         Transform transform = holder.getTransform();
         if (transform.isIdentity()) {
             clipboard.paste(extent, mutable, false);

worldedit-core/src/main/java/com/sk89q/worldedit/EditSession.java

@@ -3881,7 +3881,7 @@ public class EditSession extends PassthroughExtent implements AutoCloseable {
     @Override
     public void addSchems(Region region, Mask mask, List<ClipboardHolder> clipboards, int rarity, boolean rotate) throws
             WorldEditException {
-        spawnResource(region, new SchemGen(mask, this, clipboards, rotate), rarity, 1);
+        spawnResource(region, new SchemGen(mask, this, clipboards, rotate, region), rarity, 1);
     }
 
     @Override

worldedit-core/src/main/java/com/sk89q/worldedit/command/BrushCommands.java

@@ -645,10 +645,10 @@ public class BrushCommands {
     @CommandPermissions("worldedit.brush.populateschematic")
     public void scatterSchemBrush(
             Player player, InjectedValueAccess context,
-            @Arg(desc = "Mask")
-                    Mask mask,
             @Arg(name = "clipboard", desc = "Clipboard uri")
                     String clipboardStr,
+            @Arg(desc = "Mask of block to place on. Defaults to solid blocks.", def = "")
+                    Mask mask,
             @Arg(desc = "Expression", def = "30")
                     Expression radius,
             @Arg(desc = "double", def = "50")

worldedit-core/src/main/java/com/sk89q/worldedit/extent/Extent.java

@@ -216,7 +216,7 @@ public interface Extent extends InputExtent, OutputExtent {
      */
 
     /**
-     * Returns the highest solid 'terrain' block.
+     * Returns the highest solid 'terrain' (movement-blocking) block.
      *
      * @param x    the X coordinate
      * @param z    the Z coordinate
@@ -225,6 +225,9 @@ public interface Extent extends InputExtent, OutputExtent {
      * @return height of highest block found or 'minY'
      */
     default int getHighestTerrainBlock(final int x, final int z, int minY, int maxY) {
+        maxY = Math.min(maxY, getMaxY());
+        minY = Math.max(getMinY(), minY);
+
         for (int y = maxY; y >= minY; --y) {
             BlockState block = getBlock(x, y, z);
             if (block.getBlockType().getMaterial().isMovementBlocker()) {
@@ -235,7 +238,7 @@ public interface Extent extends InputExtent, OutputExtent {
     }
 
     /**
-     * Returns the highest solid 'terrain' block.
+     * Returns the highest block matching the given mask.
      *
      * @param x      the X coordinate
      * @param z      the Z coordinate
@@ -245,6 +248,9 @@ public interface Extent extends InputExtent, OutputExtent {
      * @return height of highest block found or 'minY'
      */
     default int getHighestTerrainBlock(final int x, final int z, int minY, int maxY, Mask filter) {
+        if (filter == null) {
+            return getHighestTerrainBlock(x, z, minY, maxY);
+        }
         maxY = Math.min(maxY, getMaxY());
         minY = Math.max(getMinY(), minY);
 
@@ -259,9 +265,7 @@ public interface Extent extends InputExtent, OutputExtent {
     }
 
     /**
-     * Returns the nearest surface layer (up/down from start)
-     * <p>
-     * TODO: Someone understand this..?
+     * Returns the nearest surface layer (up/down from start), where a layer is 1/16th of a block to allow for snow, liquid, etc.
      *
      * @param x    x to search from
      * @param z    y to search from
@@ -271,6 +275,9 @@ public interface Extent extends InputExtent, OutputExtent {
      * @return nearest surface layer
      */
     default int getNearestSurfaceLayer(int x, int z, int y, int minY, int maxY) {
+        maxY = Math.min(maxY, getMaxY());
+        minY = Math.max(getMinY(), minY);
+
         int clearanceAbove = maxY - y;
         int clearanceBelow = y - minY;
         int clearance = Math.min(clearanceAbove, clearanceBelow);
@@ -331,6 +338,9 @@ public interface Extent extends InputExtent, OutputExtent {
      * @return The y value of the nearest terrain block
      */
     default int getNearestSurfaceTerrainBlock(int x, int z, int y, int minY, int maxY, int failedMin, int failedMax, Mask mask) {
+        maxY = Math.min(maxY, getMaxY());
+        minY = Math.max(getMinY(), minY);
+
         y = Math.max(minY, Math.min(maxY, y));
         int clearanceAbove = maxY - y;
         int clearanceBelow = y - minY;
@@ -438,6 +448,9 @@ public interface Extent extends InputExtent, OutputExtent {
             int failedMax,
             boolean ignoreAir
     ) {
+        maxY = Math.min(maxY, getMaxY());
+        minY = Math.max(getMinY(), minY);
+
         y = Math.max(minY, Math.min(maxY, y));
         int clearanceAbove = maxY - y;
         int clearanceBelow = y - minY;
@@ -494,7 +507,7 @@ public interface Extent extends InputExtent, OutputExtent {
 
     default void addSchems(Region region, Mask mask, List<ClipboardHolder> clipboards, int rarity, boolean rotate) throws
             WorldEditException {
-        spawnResource(region, new SchemGen(mask, this, clipboards, rotate), rarity, 1);
+        spawnResource(region, new SchemGen(mask, this, clipboards, rotate, region), rarity, 1);
     }
 
     default void spawnResource(Region region, Resource gen, int rarity, int frequency) throws WorldEditException {