update set adn get field string access in iterator + new exemple

Author: elebras1

examples/src/main/java/com/github/elebras1/flecs/examples/MultiThreadedSystemExemple.java

@@ -0,0 +1,46 @@
+package com.github.elebras1.flecs.examples;
+
+import com.github.elebras1.flecs.*;
+import com.github.elebras1.flecs.examples.components.Minister;
+import com.github.elebras1.flecs.util.FlecsConstants;
+
+import java.util.Random;
+
+public class MultiThreadedSystemExemple {
+    public static void main(String[] args) {
+        try (World world = new World()) {
+            System.out.println("=== Test Multithreaded system + native access ===");
+            world.component(Minister.class);
+            world.setThreads(4);
+
+            Random rnd = new Random();
+            for (int i = 0; i < 1000; i++) {
+                world.obtainEntity(world.entity("Min_" + i)).set(new Minister("M-" + i, "default.png", rnd.nextFloat() * 50, 2020, 0));
+            }
+
+            world.system("LoyaltySystem")
+                    .with(Minister.class)
+                    .kind(FlecsConstants.EcsOnUpdate)
+                    .multiThreaded(true)
+                    .iter(it -> {
+                        int count = it.count();
+                        for (int i = 0; i < count; i++) {
+                            float loyalty = it.fieldFloat(Minister.class, 0, "loyalty", i);
+
+                            float newLoyalty = Math.min(loyalty + 10.0f, 100.0f);
+                            String newImg = newLoyalty > 50 ? "happy.png" : "angry.png";
+
+                            it.setFieldFloat(Minister.class, 0, "loyalty", i, newLoyalty);
+                            it.setFieldString(Minister.class, 0, "imageFileName", i, newImg);
+                        }
+                    });
+
+            for (int f = 0; f < 5; f++) {
+                world.progress(0.016f);
+            }
+
+            Minister m = world.obtainEntity(world.lookup("Min_42")).get(Minister.class);
+            System.out.printf("Check Min_42 -> Loyalty: %.1f | Img: %s%n", m.loyalty(), m.imageFileName());
+        }
+    }
+}

src/main/java/com/github/elebras1/flecs/Iter.java

@@ -1,5 +1,6 @@
 package com.github.elebras1.flecs;
 
+import java.lang.foreign.MemoryLayout;
 import java.lang.foreign.MemorySegment;
 import java.lang.foreign.ValueLayout;
 import java.util.Arrays;
@@ -174,13 +175,9 @@ public <T> byte fieldByte(Class<T> componentClass, int index, String fieldName,
 
     public <T> String fieldString(Class<T> componentClass, int index, String fieldName, int i) {
         long offset = fieldPtr(componentClass, index, fieldName, i);
-        MemorySegment stringPointer = this.cachedColumns[index].get(ValueLayout.ADDRESS.withByteAlignment(1), offset);
-
-        if (stringPointer.address() == 0) {
-            return null;
-        }
-
-        return stringPointer.reinterpret(Short.MAX_VALUE).getString(0);
+        Component<T> component = this.world.componentRegistry().getComponent(componentClass);
+        long capacity = component.layout().select(MemoryLayout.PathElement.groupElement(fieldName)).byteSize();
+        return this.cachedColumns[index].asSlice(offset, capacity).getString(0);
     }
 
     public <T> void setFieldInt(Class<T> componentClass, int index, String fieldName, int i, int value) {
@@ -219,7 +216,18 @@ public <T> void setFieldByte(Class<T> componentClass, int index, String fieldNam
     }
 
     public <T> void setFieldString(Class<T> componentClass, int index, String fieldName, int i, String value) {
-        throw new UnsupportedOperationException("setFieldString not yet implemented");
+        long offset = fieldPtr(componentClass, index, fieldName, i);
+        Component<T> component = this.world.componentRegistry().getComponent(componentClass);
+        long capacity = component.layout().select(MemoryLayout.PathElement.groupElement(fieldName)).byteSize();
+        MemorySegment slice = this.cachedColumns[index].asSlice(offset, capacity);
+        if (value == null || value.isEmpty()) {
+            slice.set(ValueLayout.JAVA_BYTE, 0, (byte) 0);
+            return;
+        }
+        byte[] bytes = value.getBytes(java.nio.charset.StandardCharsets.UTF_8);
+        int len = Math.min(bytes.length, (int) capacity - 1);
+        MemorySegment.copy(bytes, 0, slice, ValueLayout.JAVA_BYTE, 0, len);
+        slice.set(ValueLayout.JAVA_BYTE, len, (byte) 0);
     }
 
     public long event() {