apply vanilla uvlock under blockstate x/y rotations and face zero-thickness elements towards the ray

x rotations without uvlock already sampled the model-space element like
vanilla (lying logs/pillars, vertical observers/dispensers verified against
FaceBakery for every blockstate variant). The remaining divergence was
uvlock: faces kept model-extent UVs and were sampled in world orientation,
so top stairs, ceiling buttons, fences/walls and ceiling vines showed
shifted or rotated textures. Rotated uvlocked elements now also go through
the model-space path, with each face's final UVs mapped by vanilla's
BlockMath face transformation (inverted, as in FaceBakery).

Zero-thickness elements (vine, lichen) always reported their low face;
pick the face turned towards the ray instead.

Edge-case test plugin: xrot/xrot2 scenes (lying pillars, vertical
observers/dispensers/droppers, top stairs, ceiling buttons).

src/main/java/eu/mhsl/minecraft/pixelpics/assets/ModelBaker.java

@@ -96,9 +96,13 @@ public final class ModelBaker {
                 }
             }
 
-            // Without uvlock, textures turn with the model (vanilla): keep the model-space element so the
-            // intersectors can sample it exactly. With uvlock they stay world-aligned (the rotated faces).
-            Element unrotated = (!variant.uvlock() && (xSteps != 0 || ySteps != 0)) ? modelElement : null;
+            // Rotated variants keep the model-space element; intersectors hit it with the inverse-rotated ray
+            // (vanilla bakes the same way). Without uvlock the textures thus turn with the model; with uvlock
+            // each face's final UVs are additionally transformed so the texture stays world-aligned.
+            Element unrotated = null;
+            if (xSteps != 0 || ySteps != 0) {
+                unrotated = variant.uvlock() ? uvLocked(modelElement, xSteps, ySteps) : modelElement;
+            }
             baked.add(new Element(from, to, faces, rotOrigin, rotAxis, rotAngle, rescale, unrotated, xSteps, ySteps));
 
             // Accumulate average color from the element's face textures.
@@ -149,6 +153,50 @@ public final class ModelBaker {
         };
     }
 
+    /** The model-space element with every face's UVs locked to the world under the given rotation. */
+    private static Element uvLocked(Element e, int xSteps, int ySteps) {
+        Face[] locked = new Face[6];
+        for (Direction d : Direction.values()) {
+            Face f = e.faces[d.ordinal()];
+            if (f != null) locked[d.ordinal()] = f.withUvLock(uvLockTransform(d, xSteps, ySteps));
+        }
+        return new Element(e.from, e.to, locked, e.rotOrigin, e.rotAxis, e.rotAngleRad, e.rescale);
+    }
+
+    /**
+     * Vanilla uvlock ({@code BlockMath.getFaceTransformation}, inverted as in {@code FaceBakery}): the final
+     * texture coordinates of model face {@code d}, centred on the texture, are mapped by
+     * {@code M = G2L(d) · R⁻¹ · L2G(D)} where R is the blockstate rotation, D the world face {@code d} turns into,
+     * and L2G the per-face UV frames (south = identity). For side faces this keeps the texture world-aligned;
+     * up/down under x rotations follow vanilla's frames (not strictly world-aligned). M is one of the 8 symmetries
+     * of the unit UV square, returned as the affine of {@link Face#uvLock}.
+     */
+    static double[] uvLockTransform(Direction d, int xSteps, int ySteps) {
+        Direction world = d.rotateX(xSteps).rotateY(ySteps);
+        double[] cu = lockAxis(d, world, 1, 0, xSteps, ySteps);
+        double[] cv = lockAxis(d, world, 0, 1, xSteps, ySteps);
+        // u' = ½ + cu.x (u-½) + cv.x (v-½), v' = ½ + cu.y (u-½) + cv.y (v-½)
+        return new double[] {0.5 - 0.5 * (cu[0] + cv[0]), cu[0], cv[0], 0.5 - 0.5 * (cu[1] + cv[1]), cu[1], cv[1]};
+    }
+
+    private static double[] lockAxis(Direction d, Direction world, double u, double v, int xSteps, int ySteps) {
+        double[] w = uvFrame(world, u, v, 0, false);
+        double[] m = Element.unrotate(w[0], w[1], w[2], xSteps, ySteps, false);
+        return uvFrame(d, m[0], m[1], m[2], true);
+    }
+
+    /** Vanilla {@code BlockMath.VANILLA_UV_TRANSFORM_LOCAL_TO_GLOBAL} (or its inverse) applied to a vector. */
+    private static double[] uvFrame(Direction d, double x, double y, double z, boolean inverse) {
+        return switch (d) {
+            case SOUTH -> new double[] {x, y, z};
+            case NORTH -> new double[] {-x, y, -z}; // rotY(180°)
+            case EAST -> inverse ? new double[] {-z, y, x} : new double[] {z, y, -x}; // rotY(90°)
+            case WEST -> inverse ? new double[] {z, y, -x} : new double[] {-z, y, x}; // rotY(-90°)
+            case UP -> inverse ? new double[] {x, -z, y} : new double[] {x, z, -y}; // rotX(-90°)
+            case DOWN -> inverse ? new double[] {x, z, -y} : new double[] {x, -z, y}; // rotX(90°)
+        };
+    }
+
     private int[][] resolveTexture(String ref, Map<String, String> vars) {
         if (ref == null) return null;
         String current = ref;

src/main/java/eu/mhsl/minecraft/pixelpics/assets/model/Element.java

@@ -19,9 +19,10 @@ public final class Element {
     public final double rotAngleRad; // radians
     public final boolean rescale;
 
-    // Blockstate rotation WITHOUT uvlock: the model-space element and the 90° steps (x first, then y) that
-    // turn it into this world-space one. Textures stay bound to the model, so intersectors hit the
-    // unrotated element with the inverse-rotated ray. Null/0 when unrotated or uvlocked.
+    // Blockstate rotation: the model-space element and the 90° steps (x first, then y) that turn it into this
+    // world-space one. Intersectors hit the unrotated element with the inverse-rotated ray, so textures stay
+    // bound to the model (vanilla); under uvlock its faces carry a UV transform keeping them world-aligned.
+    // Null/0 when unrotated.
     public final Element unrotated;
     public final int xSteps;
     public final int ySteps;

src/main/java/eu/mhsl/minecraft/pixelpics/assets/model/Face.java

@@ -11,7 +11,17 @@ public final class Face {
     public final int rotation; // 0/90/180/270, applied to the sampled UV
     public final int tintIndex; // -1 = no tint
 
+    // uvlock: affine applied to the final texture (u, v) as {a, b, c, d, e, f} with u' = a + b*u + c*v and
+    // v' = d + e*u + f*v (one of the 8 symmetries of the unit square), null when not locked.
+    public final double[] uvLock;
+
     public Face(int[][] texture, double u1, double v1, double u2, double v2, int rotation, int tintIndex) {
+        this(texture, u1, v1, u2, v2, rotation, tintIndex, null);
+    }
+
+    public Face(
+            int[][] texture, double u1, double v1, double u2, double v2, int rotation, int tintIndex, double[] uvLock) {
+        this.uvLock = uvLock;
         this.texture = texture;
         this.u1 = u1;
         this.v1 = v1;
@@ -21,6 +31,16 @@ public final class Face {
         this.tintIndex = tintIndex;
     }
 
+    /** This face with another texture and tint index (UVs, rotation and uvlock kept). */
+    public Face withTexture(int[][] texture, int tintIndex) {
+        return new Face(texture, u1, v1, u2, v2, rotation, tintIndex, uvLock);
+    }
+
+    /** This face with its final texture coordinates transformed by a uvlock affine (see {@link #uvLock}). */
+    public Face withUvLock(double[] lock) {
+        return new Face(texture, u1, v1, u2, v2, rotation, tintIndex, lock);
+    }
+
     /**
      * Samples the ARGB pixel for a position within the face, where {@code (s, t)} are in 0..1 across
      * the face's two in-plane axes (s = horizontal, t = vertical, top-left origin).
@@ -48,6 +68,11 @@ public final class Face {
 
         double u = u1 + (u2 - u1) * rs;
         double v = v1 + (v2 - v1) * rt;
+        if (uvLock != null) {
+            double lu = uvLock[0] + uvLock[1] * u + uvLock[2] * v;
+            v = uvLock[3] + uvLock[4] * u + uvLock[5] * v;
+            u = lu;
+        }
 
         int h = texture.length;
         if (h == 0) return 0;

src/main/java/eu/mhsl/minecraft/pixelpics/render/entity/cem/ItemGeometry.java

@@ -110,8 +110,8 @@ public final class ItemGeometry {
         ResolvedModel model = registry.get(data);
         if (model == null || !model.hasGeometry) return;
         for (Element world : model.elements) {
-            // Rotated without uvlock: bake the model-space element turned by the blockstate rotation, so
-            // textures stay bound to the model (vanilla); otherwise the world-space element as is.
+            // Rotated: bake the model-space element turned by the blockstate rotation, so textures stay bound
+            // to the model like vanilla (uvlocked faces carry their UV transform); otherwise the element as is.
             Element e = world.unrotated != null ? world.unrotated : world;
             Affine variant = world.unrotated != null ? variantRotation(world.xSteps, world.ySteps) : Affine.identity();
             Face[] faces = new Face[6];
@@ -468,6 +468,6 @@ public final class ItemGeometry {
                 return copy;
             });
         }
-        return new Face(t, f.u1, f.v1, f.u2, f.v2, f.rotation, -1);
+        return f.withTexture(t, -1);
     }
 }

src/main/java/eu/mhsl/minecraft/pixelpics/render/raytrace/ElementIntersector.java

@@ -45,8 +45,8 @@ public final class ElementIntersector {
             Element element = model.elements.get(i);
             Candidate c;
             if (element.unrotated != null) {
-                // Blockstate rotation without uvlock: hit the model-space element with the inverse-rotated ray
-                // (same t: rigid transform), so faces and UVs stay bound to the model like in vanilla.
+                // Blockstate rotation: hit the model-space element with the inverse-rotated ray (same t: rigid
+                // transform), so faces and UVs stay bound to the model like in vanilla (uvlock: see Face#uvLock).
                 Element m = element.unrotated;
                 double[] mo = Element.unrotate(ox, oy, oz, element.xSteps, element.ySteps, true);
                 double[] md = Element.unrotate(dx, dy, dz, element.xSteps, element.ySteps, false);
@@ -130,12 +130,13 @@ public final class ElementIntersector {
             double inv = 1.0 / d[a];
             double t1 = (from[a] - o[a]) * inv;
             double t2 = (to[a] - o[a]) * inv;
-            boolean neg = true;
+            // Entered through the low face when travelling +axis. Decided by the direction, not t1 > t2, so
+            // zero-thickness elements (vines, lichen: from == to) show the face turned towards the ray.
+            boolean neg = inv > 0;
             if (t1 > t2) {
                 double tmp = t1;
                 t1 = t2;
                 t2 = tmp;
-                neg = false;
             }
             if (t1 > tmin) {
                 tmin = t1;

tools/edgecase-plugin/pptest/PPTest.java

@@ -56,6 +56,9 @@ public class PPTest extends JavaPlugin {
         scenes.put("pistondown", new Scene("pistondown", this::piston, -1.6, 2.6, -1.6, 0.5, 1.4, 0.5));
         scenes.put("pistonup", new Scene("pistonup", this::piston, 0.4, 2.6, -1.6, 2.5, 1.4, 0.5));
         scenes.put("vehicles", new Scene("vehicles", this::vehicles, 5, 3, -7, 5, 0.6, 1.5));
+        // Blockstate x rotations (+ x/y combined, uvlock): lying pillars, vertical observers/dispensers, top stairs.
+        scenes.put("xrot", new Scene("xrot", this::xrot, 3.5, 5.5, -4.5, 6, 0.5, 3.5));
+        scenes.put("xrot2", new Scene("xrot2", this::xrot, 11, 5, 10.5, 6, 0.5, 3.5));
         // Chests: same layout seen from all four sides (single/double per facing, trapped, ender, copper).
         scenes.put("chests_s", new Scene("chests_s", this::chests, 4.5, 5, 13, 4.5, 0, 3));
         scenes.put("chests_n", new Scene("chests_n", this::chests, 4.5, 5, -7, 4.5, 0, 3));
@@ -491,6 +494,38 @@ public class PPTest extends JavaPlugin {
         o.clone().add(4, 0, -2).getBlock().setBlockData(Bukkit.createBlockData("minecraft:furnace[facing=north]"), false);
     }
 
+    /**
+     * Row z=0: oak log, basalt, quartz pillar, hay bale lying along x (x=90,y=90) and z (x=90). Row z=3: observer,
+     * dispenser, dropper facing up and down. Row z=6: oak and stone-brick stairs half=top in all four facings
+     * (x=180 + uvlock), oak buttons on the ceiling. A stone column at z=-2 marks north.
+     */
+    private void xrot(Location o) {
+        java.util.function.BiConsumer<int[], String> put = (p, data) -> o.clone().add(p[0], p[1], p[2]).getBlock()
+                .setBlockData(Bukkit.createBlockData("minecraft:" + data), false);
+        String[] pillars = {"oak_log", "basalt", "quartz_pillar", "hay_block"};
+        for (int i = 0; i < pillars.length; i++) {
+            put.accept(new int[] {i * 3, 0, 0}, pillars[i] + "[axis=x]");
+            put.accept(new int[] {i * 3 + 1, 0, 0}, pillars[i] + "[axis=z]");
+        }
+        String[] vertical = {"observer", "dispenser", "dropper"};
+        for (int i = 0; i < vertical.length; i++) {
+            put.accept(new int[] {i * 3, 0, 3}, vertical[i] + "[facing=up]");
+            put.accept(new int[] {i * 3 + 1, 1, 3}, vertical[i] + "[facing=down]");
+            put.accept(new int[] {i * 3 + 1, 0, 3}, "glass");
+        }
+        String[] f = {"north", "east", "south", "west"};
+        for (int i = 0; i < f.length; i++) {
+            put.accept(new int[] {i * 2, 0, 6}, "oak_stairs[facing=" + f[i] + ",half=top]");
+            put.accept(new int[] {i * 2 + 1, 0, 6}, "stone_brick_stairs[facing=" + f[i] + ",half=top]");
+        }
+        put.accept(new int[] {9, 1, 6}, "stone");
+        put.accept(new int[] {9, 0, 6}, "oak_button[face=ceiling,facing=north]");
+        put.accept(new int[] {10, 1, 6}, "stone");
+        put.accept(new int[] {10, 0, 6}, "oak_button[face=ceiling,facing=east]");
+        put.accept(new int[] {0, 0, -2}, "stone");
+        put.accept(new int[] {0, 1, -2}, "stone");
+    }
+
     private void vehicles(Location o) {
         spawn(o, 0, 0, 0, 0, EntityType.CHEST_MINECART);
         spawn(o, 1.8, 0, 0, 90, EntityType.FURNACE_MINECART);