Particlebugfix

fxgl-entity/src/main/java/com/almasb/fxgl/particle/Particle.java

@@ -252,9 +252,19 @@ boolean update(double tpf) {
 
             // From https://stackoverflow.com/questions/17113234/affine-transform-scale-around-a-point
             // x = S(x – c) + c = Sx + (c – Sc)
-            var sx = (scaleOrigin.x + x - entityScale.x * (scaleOrigin.x + x)) + entityScale.y * x;
+
+            //scale origin and entity scale are 2d points, when referencing the x and y values these are
+            //the corresponding points            
+            var sx = (scaleOrigin.x + x - entityScale.x * (scaleOrigin.x + x)) + entityScale.x * x;
+            //sx = (x plus the scale of x from origin - center of where particle comes from) + scaled centre of particle
+            //sx = (x on the page, including origin - center of where particle comes from + sc
+
             var sy = (scaleOrigin.y + y - entityScale.y * (scaleOrigin.y + y)) + entityScale.y * y;
 
+            //x = sx + (c - Sc)
+            //sx = x - (c - Sc) = x - c + Sc
+            //S is the scaling transformation, and c is the center in coordinates relative to the top left.
+
             getView().setLayoutX(sx);
             getView().setLayoutY(sy);
 

fxgl-samples/src/main/java/intermediate/particles/ParticleScaleSample2.java

@@ -0,0 +1,68 @@
+package intermediate.particles;
+
+import com.almasb.fxgl.animation.Interpolators;
+import com.almasb.fxgl.app.GameApplication;
+import com.almasb.fxgl.app.GameSettings;
+import com.almasb.fxgl.core.math.FXGLMath;
+import com.almasb.fxgl.dsl.components.ExpireCleanComponent;
+import com.almasb.fxgl.dsl.components.ProjectileComponent;
+import com.almasb.fxgl.particle.ParticleComponent;
+import com.almasb.fxgl.particle.ParticleEmitters;
+import javafx.geometry.Point2D;
+import javafx.scene.effect.BlendMode;
+import javafx.scene.paint.Color;
+import javafx.scene.shape.Circle;
+import javafx.util.Duration;
+
+import java.util.function.Supplier;
+
+import static com.almasb.fxgl.dsl.FXGL.*;
+import static com.almasb.fxgl.dsl.FXGL.entityBuilder;
+import static com.almasb.fxgl.dsl.FXGL.random;
+import static com.almasb.fxgl.dsl.FXGL.runOnce;
+import static com.almasb.fxgl.dsl.FXGL.texture;
+
+public class ParticleScaleSample2 extends GameApplication{
+    @Override
+    protected void initSettings(GameSettings settings) {
+        settings.setWidth(1280);
+        settings.setHeight(720);
+    }
+
+    @Override
+    protected void initGame() {
+        getGameScene().setBackgroundColor(Color.BLACK);
+
+        //this circle has a difference in the x and the y points in the scale
+        spawnMinor(new Point2D(450, 300), false);
+
+        //this cricle has the same x and y points in the scale
+        spawnMinor(new Point2D(450, 300), true);
+
+        //both of their locations are the same, they should spawn in the same space. but because the x point is affected by the scale, the circles appear in different locations.
+        //this shows the biggest issue with this bug, the x value is being affected by the y scale, when it should not be. 
+    }
+
+    private void spawnMinor(Point2D p, Boolean pointsTheSame) {
+        var emitter = ParticleEmitters.newExplosionEmitter(17);
+
+        //this sets the new points to be either the same or different
+        if (pointsTheSame) {
+            emitter.setEntityScaleFunction(() -> new Point2D(1, 1));
+        } else {
+            emitter.setEntityScaleFunction(() -> new Point2D(1, 2));
+        }
+        emitter.setExpireFunction(i -> Duration.seconds(10));
+        emitter.setSize(10, 20);
+        entityBuilder()
+                .at(p)
+                .with(new ParticleComponent(emitter))
+                .with(new ExpireCleanComponent(Duration.seconds(3)).animateOpacity())
+                .zIndex(100)
+                .buildAndAttach();
+    }
+
+    public static void main(String[] args) {
+        launch(args);
+    }
+}