Cheaper ellipsoid deposit cells

- squared y/z offsets computed once per sphere row, same evaluation order
- test pins cells, order and RNG draws against the per-cell form

core/src/main/java/art/arcane/iris/generation/decoration/IrisDepositGenerator.java

@@ -304,7 +304,12 @@ public class IrisDepositGenerator {
         return new ClumpFootprint(cells.extentX * 2 + 1, cells.minY, false);
     }
 
-    private static void vanillaEllipsoidCells(RNG rng, int size, CellSink sink) {
+    /**
+     * Emits the clump's cells sphere by sphere in x, y, z order, duplicates included. The squared y and z
+     * offsets are computed once per sphere row; the sums keep the per-cell evaluation order, so every cell
+     * test is bit-identical to evaluating {@code nx * nx + ny * ny + nz * nz} in place.
+     */
+    static void vanillaEllipsoidCells(RNG rng, int size, CellSink sink) {
         float angle = rng.nextFloat() * (float) Math.PI;
         float reach = size / 8F;
         double startX = Math.sin(angle) * reach;
@@ -347,6 +352,8 @@ public class IrisDepositGenerator {
             }
         }
 
+        double[] squaredY = new double[16];
+        double[] squaredZ = new double[16];
         for (int i = 0; i < size; i++) {
             double radius = nodes[i * 4 + 3];
             if (radius < 0D) {
@@ -361,21 +368,37 @@ public class IrisDepositGenerator {
             int maxY = Math.max((int) Math.floor(centerY + radius), minY);
             int minZ = (int) Math.floor(centerZ - radius);
             int maxZ = Math.max((int) Math.floor(centerZ + radius), minZ);
+            int spanY = maxY - minY + 1;
+            int spanZ = maxZ - minZ + 1;
+            if (spanY > squaredY.length) {
+                squaredY = new double[spanY];
+            }
+            if (spanZ > squaredZ.length) {
+                squaredZ = new double[spanZ];
+            }
+            for (int y = 0; y < spanY; y++) {
+                double ny = (minY + y + 0.5D - centerY) / radius;
+                squaredY[y] = ny * ny;
+            }
+            for (int z = 0; z < spanZ; z++) {
+                double nz = (minZ + z + 0.5D - centerZ) / radius;
+                squaredZ[z] = nz * nz;
+            }
 
             for (int x = minX; x <= maxX; x++) {
                 double nx = (x + 0.5D - centerX) / radius;
-                if (nx * nx >= 1D) {
+                double squaredX = nx * nx;
+                if (squaredX >= 1D) {
                     continue;
                 }
-                for (int y = minY; y <= maxY; y++) {
+                for (int y = 0; y < spanY; y++) {
-                    double ny = (y + 0.5D - centerY) / radius;
+                    double squaredXY = squaredX + squaredY[y];
-                    if (nx * nx + ny * ny >= 1D) {
+                    if (squaredXY >= 1D) {
                         continue;
                     }
-                    for (int z = minZ; z <= maxZ; z++) {
+                    for (int z = 0; z < spanZ; z++) {
-                        double nz = (z + 0.5D - centerZ) / radius;
+                        if (squaredXY + squaredZ[z] < 1D) {
-                        if (nx * nx + ny * ny + nz * nz < 1D) {
+                            sink.add(x, minY + y, minZ + z);
-                            sink.add(x, y, z);
                         }
                     }
                 }
@@ -601,7 +624,7 @@ public class IrisDepositGenerator {
     }
 
     @FunctionalInterface
-    private interface CellSink {
+    interface CellSink {
         void add(int x, int y, int z);
     }
 

core/src/test/java/art/arcane/iris/generation/decoration/IrisDepositEllipsoidCellsTest.java

@@ -0,0 +1,113 @@
+package art.arcane.iris.generation.decoration;
+
+import art.arcane.volmlib.util.math.RNG;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+public class IrisDepositEllipsoidCellsTest {
+    @Test
+    public void cellsAndDrawsMatchThePerCellEvaluation() {
+        int[] sizes = {1, 2, 3, 4, 5, 7, 8, 9, 12, 16, 17, 24, 32, 33, 48, 64, 96, 200};
+        for (int size : sizes) {
+            long seeds = size <= 64 ? 300L : 8L;
+            for (long seed = 0L; seed < seeds; seed++) {
+                long mixedSeed = seed * 0x9E3779B97F4A7C15L + size;
+                RNG expectedRng = new RNG(mixedSeed);
+                RNG actualRng = new RNG(mixedSeed);
+                List<Long> expected = new ArrayList<>();
+                List<Long> actual = new ArrayList<>();
+                referenceCells(expectedRng, size, (x, y, z) -> expected.add(pack(x, y, z)));
+                IrisDepositGenerator.vanillaEllipsoidCells(actualRng, size, (x, y, z) -> actual.add(pack(x, y, z)));
+                assertEquals("size " + size + " seed " + seed, expected, actual);
+                assertEquals("size " + size + " seed " + seed, expectedRng.nextLong(), actualRng.nextLong());
+            }
+        }
+    }
+
+    private static long pack(int x, int y, int z) {
+        return ((long) (x & 0x1FFFFF) << 42) | ((long) (y & 0x1FFFFF) << 21) | (z & 0x1FFFFF);
+    }
+
+    private static void referenceCells(RNG rng, int size, IrisDepositGenerator.CellSink sink) {
+        float angle = rng.nextFloat() * (float) Math.PI;
+        float reach = size / 8F;
+        double startX = Math.sin(angle) * reach;
+        double endX = -Math.sin(angle) * reach;
+        double startZ = Math.cos(angle) * reach;
+        double endZ = -Math.cos(angle) * reach;
+        double startY = rng.nextInt(3) - 2;
+        double endY = rng.nextInt(3) - 2;
+        double[] nodes = new double[size * 4];
+
+        for (int i = 0; i < size; i++) {
+            float progress = (float) i / size;
+            double radiusNoise = rng.nextDouble() * size / 16D;
+            nodes[i * 4] = startX + (endX - startX) * progress;
+            nodes[i * 4 + 1] = startY + (endY - startY) * progress;
+            nodes[i * 4 + 2] = startZ + (endZ - startZ) * progress;
+            nodes[i * 4 + 3] = ((Math.sin(Math.PI * progress) + 1D) * radiusNoise + 1D) / 2D;
+        }
+
+        for (int i = 0; i < size - 1; i++) {
+            if (nodes[i * 4 + 3] <= 0D) {
+                continue;
+            }
+            for (int j = i + 1; j < size; j++) {
+                if (nodes[j * 4 + 3] <= 0D) {
+                    continue;
+                }
+                double dx = nodes[i * 4] - nodes[j * 4];
+                double dy = nodes[i * 4 + 1] - nodes[j * 4 + 1];
+                double dz = nodes[i * 4 + 2] - nodes[j * 4 + 2];
+                double dr = nodes[i * 4 + 3] - nodes[j * 4 + 3];
+                if (dr * dr <= dx * dx + dy * dy + dz * dz) {
+                    continue;
+                }
+                if (dr > 0D) {
+                    nodes[j * 4 + 3] = -1D;
+                } else {
+                    nodes[i * 4 + 3] = -1D;
+                }
+            }
+        }
+
+        for (int i = 0; i < size; i++) {
+            double radius = nodes[i * 4 + 3];
+            if (radius < 0D) {
+                continue;
+            }
+            double centerX = nodes[i * 4];
+            double centerY = nodes[i * 4 + 1];
+            double centerZ = nodes[i * 4 + 2];
+            int minX = (int) Math.floor(centerX - radius);
+            int maxX = Math.max((int) Math.floor(centerX + radius), minX);
+            int minY = (int) Math.floor(centerY - radius);
+            int maxY = Math.max((int) Math.floor(centerY + radius), minY);
+            int minZ = (int) Math.floor(centerZ - radius);
+            int maxZ = Math.max((int) Math.floor(centerZ + radius), minZ);
+
+            for (int x = minX; x <= maxX; x++) {
+                double nx = (x + 0.5D - centerX) / radius;
+                if (nx * nx >= 1D) {
+                    continue;
+                }
+                for (int y = minY; y <= maxY; y++) {
+                    double ny = (y + 0.5D - centerY) / radius;
+                    if (nx * nx + ny * ny >= 1D) {
+                        continue;
+                    }
+                    for (int z = minZ; z <= maxZ; z++) {
+                        double nz = (z + 0.5D - centerZ) / radius;
+                        if (nx * nx + ny * ny + nz * nz < 1D) {
+                            sink.add(x, y, z);
+                        }
+                    }
+                }
+            }
+        }
+    }
+}