Fix #1773 (Wrong particle position when `worldSpace` flag equals to true) (#1889)

* Add test case for issue #1773.

* Fix wrong particle position when using 'EmitterMeshVertexShape' or 'EmitterMeshFaceShape' and worldSpace flag equal to true. The old code was interpolating particles position toward emitter world position and this was only working fine for EmitterPointShape and in the other shapes this was causing particles not keep the shape because they were being dragged toward emitter position. The new code calculates the distance vector from emitter last location to the current emitter location and subtracts it from particles position to generate a hypothetical position that is used for interpolation.

* Add javadoc to TestIssue1773.

* Minor javadoc fix.

jme3-core/src/main/java/com/jme3/effect/ParticleEmitter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2009-2021 jMonkeyEngine
+ * Copyright (c) 2009-2023 jMonkeyEngine
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -1081,6 +1081,12 @@ public class ParticleEmitter extends Geometry {
             }
         }
 
+        // Emitter distance from last location
+        Vector3f lastDistance = null;
+        if (lastPos != null && isInWorldSpace()) {
+            lastDistance = getWorldTranslation().subtract(lastPos, lastPos);
+        }
+
         // Spawns particles within the tpf timeslot with proper age
         float interval = 1f / particlesPerSec;
         float originalTpf = tpf;
@@ -1091,6 +1097,11 @@ public class ParticleEmitter extends Geometry {
             if (p != null) {
                 p.life -= tpf;
                 if (lastPos != null && isInWorldSpace()) {
+                    // Generate a hypothetical position by subtracting distance
+                    // vector from particle position and use for interpolating
+                    // particle. This will fix discrete particles motion when
+                    // emitter is moving fast. - Ali-RS 2023-1-2
+                    Vector3f lastPos = p.position.subtract(lastDistance, temp);
                     p.position.interpolateLocal(lastPos, 1 - tpf / originalTpf);
                 }
                 if (p.life <= 0) {

jme3-examples/src/main/java/jme3test/effect/TestIssue1773.java

@@ -0,0 +1,303 @@
+/*
+ * Copyright (c) 2009-2023 jMonkeyEngine
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ * * Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * * Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ *
+ * * Neither the name of 'jMonkeyEngine' nor the names of its contributors
+ *   may be used to endorse or promote products derived from this software
+ *   without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+ * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+ * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package jme3test.effect;
+
+import com.jme3.animation.LoopMode;
+import com.jme3.app.SimpleApplication;
+import com.jme3.cinematic.MotionPath;
+import com.jme3.cinematic.events.MotionEvent;
+import com.jme3.effect.ParticleEmitter;
+import com.jme3.effect.ParticleMesh.Type;
+import com.jme3.effect.shapes.EmitterMeshVertexShape;
+import com.jme3.font.BitmapFont;
+import com.jme3.font.BitmapText;
+import com.jme3.input.KeyInput;
+import com.jme3.input.controls.ActionListener;
+import com.jme3.input.controls.KeyTrigger;
+import com.jme3.input.controls.Trigger;
+import com.jme3.light.AmbientLight;
+import com.jme3.light.DirectionalLight;
+import com.jme3.material.Material;
+import com.jme3.material.Materials;
+import com.jme3.math.ColorRGBA;
+import com.jme3.math.FastMath;
+import com.jme3.math.Vector2f;
+import com.jme3.math.Vector3f;
+import com.jme3.post.FilterPostProcessor;
+import com.jme3.post.filters.BloomFilter;
+import com.jme3.post.filters.FXAAFilter;
+import com.jme3.renderer.queue.RenderQueue;
+import com.jme3.scene.Geometry;
+import com.jme3.scene.Node;
+import com.jme3.scene.shape.CenterQuad;
+import com.jme3.scene.shape.Torus;
+import com.jme3.shadow.DirectionalLightShadowFilter;
+import com.jme3.system.AppSettings;
+import com.jme3.texture.Texture;
+import java.util.Arrays;
+
+/**
+ * Test case for Issue 1773 (Wrong particle position when using
+ * 'EmitterMeshVertexShape' or 'EmitterMeshFaceShape' and worldSpace
+ * flag equal to true)
+ *
+ * If the test succeeds, the particles will be generated from the vertices
+ * (for EmitterMeshVertexShape) or from the faces (for EmitterMeshFaceShape)
+ * of the torus mesh. If the test fails, the particles will appear in the
+ * center of the torus when worldSpace flag is set to true.
+ *
+ * @author capdevon
+ */
+public class TestIssue1773 extends SimpleApplication implements ActionListener {
+
+    public static void main(String[] args) {
+        TestIssue1773 app = new TestIssue1773();
+        AppSettings settings = new AppSettings(true);
+        settings.setResolution(1280, 720);
+        settings.setRenderer(AppSettings.LWJGL_OPENGL32);
+        app.setSettings(settings);
+        app.setPauseOnLostFocus(false);
+        app.setShowSettings(false);
+        app.start();
+    }
+
+    private ParticleEmitter emit;
+    private Node myModel;
+    private BitmapText emitUI;
+    private MotionEvent motionControl;
+    private boolean playing;
+
+    @Override
+    public void simpleInitApp() {
+
+        BitmapText hud = createTextUI(ColorRGBA.White, 20, 15);
+        hud.setText("Play/Pause Motion: KEY_SPACE, InWorldSpace: KEY_I");
+
+        emitUI = createTextUI(ColorRGBA.Blue, 20, 15 * 2);
+
+        configCamera();
+        setupLights();
+        setupGround();
+        setupCircle();
+        createMotionControl();
+        setupKeys();
+    }
+
+    /**
+     * Crates particle emitter and adds it to root node.
+     */
+    private void setupCircle() {
+        myModel = new Node("FieryCircle");
+
+        Geometry torus = createTorus(1f);
+        myModel.attachChild(torus);
+
+        emit = createParticleEmitter(torus, true);
+        myModel.attachChild(emit);
+
+        rootNode.attachChild(myModel);
+    }
+
+    /**
+     * Creates torus geometry used for the emitter shape.
+     */
+    private Geometry createTorus(float radius) {
+        float s = radius / 8f;
+        Geometry geo = new Geometry("CircleXZ", new Torus(64, 4, s, radius));
+        Material mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
+        mat.setColor("Color", ColorRGBA.Blue);
+        mat.getAdditionalRenderState().setWireframe(true);
+        geo.setMaterial(mat);
+        return geo;
+    }
+
+    /**
+     * Creates a particle emitter that will emit the particles from
+     * the given shape's vertices.
+     */
+    private ParticleEmitter createParticleEmitter(Geometry geo, boolean pointSprite) {
+        Type type = pointSprite ? Type.Point : Type.Triangle;
+        ParticleEmitter emitter = new ParticleEmitter("Emitter", type, 1000);
+        Material mat = new Material(assetManager, "Common/MatDefs/Misc/Particle.j3md");
+        mat.setTexture("Texture", assetManager.loadTexture("Effects/Smoke/Smoke.png"));
+        mat.setBoolean("PointSprite", pointSprite);
+        emitter.setMaterial(mat);
+        emitter.setLowLife(1);
+        emitter.setHighLife(1);
+        emitter.setImagesX(15);
+        emitter.setStartSize(0.04f);
+        emitter.setEndSize(0.02f);
+        emitter.setStartColor(ColorRGBA.Orange);
+        emitter.setEndColor(ColorRGBA.Red);
+        emitter.setParticlesPerSec(900);
+        emitter.setGravity(0, 0f, 0);
+        //emitter.getParticleInfluencer().setVelocityVariation(1);
+        //emitter.getParticleInfluencer().setInitialVelocity(new Vector3f(0, .5f, 0));
+        emitter.setShape(new EmitterMeshVertexShape(Arrays.asList(geo.getMesh())));
+        //emitter.setShape(new EmitterMeshFaceShape(Arrays.asList(geo.getMesh())));
+        return emitter;
+    }
+
+    /**
+     * Creates a motion control that will move particle emitter in
+     * a circular path.
+     */
+    private void createMotionControl() {
+
+        float radius = 5f;
+        float height = 1.10f;
+
+        MotionPath path = new MotionPath();
+        path.setCycle(true);
+
+        for (int i = 0; i < 8; i++) {
+            float x = FastMath.sin(FastMath.QUARTER_PI * i) * radius;
+            float z = FastMath.cos(FastMath.QUARTER_PI * i) * radius;
+            path.addWayPoint(new Vector3f(x, height, z));
+        }
+        //path.enableDebugShape(assetManager, rootNode);
+
+        motionControl = new MotionEvent(myModel, path);
+        motionControl.setLoopMode(LoopMode.Loop);
+        //motionControl.setInitialDuration(15f);
+        //motionControl.setSpeed(2f);
+        motionControl.setDirectionType(MotionEvent.Direction.Path);
+    }
+
+    /**
+     * Use keyboard space key to toggle emitter motion and I key to
+     * toggle inWorldSpace flag. By default, inWorldSpace flag is on
+     * and emitter motion is off.
+     */
+    private void setupKeys() {
+        addMapping("ToggleMotionEvent", new KeyTrigger(KeyInput.KEY_SPACE));
+        addMapping("InWorldSpace", new KeyTrigger(KeyInput.KEY_I));
+    }
+
+    private void addMapping(String mappingName, Trigger... triggers) {
+        inputManager.addMapping(mappingName, triggers);
+        inputManager.addListener(this, mappingName);
+    }
+
+    @Override
+    public void onAction(String name, boolean isPressed, float tpf) {
+        if (name.equals("InWorldSpace") && isPressed) {
+            boolean worldSpace = emit.isInWorldSpace();
+            emit.setInWorldSpace(!worldSpace);
+
+        } else if (name.equals("ToggleMotionEvent") && isPressed) {
+            if (playing) {
+                playing = false;
+                motionControl.pause();
+            } else {
+                playing = true;
+                motionControl.play();
+            }
+        }
+    }
+
+    @Override
+    public void simpleUpdate(float tpf) {
+        emitUI.setText("InWorldSpace: " + emit.isInWorldSpace());
+    }
+
+    private void configCamera() {
+        flyCam.setDragToRotate(true);
+        flyCam.setMoveSpeed(10);
+
+        cam.setLocation(new Vector3f(0, 6f, 9.2f));
+        cam.lookAt(Vector3f.UNIT_Y, Vector3f.UNIT_Y);
+
+        float aspect = (float) cam.getWidth() / cam.getHeight();
+        cam.setFrustumPerspective(45, aspect, 0.1f, 1000f);
+    }
+
+    /**
+     * Adds a ground to the scene
+     */
+    private void setupGround() {
+        CenterQuad quad = new CenterQuad(12, 12);
+        quad.scaleTextureCoordinates(new Vector2f(2, 2));
+        Geometry floor = new Geometry("Floor", quad);
+        Material mat = new Material(assetManager, Materials.LIGHTING);
+        Texture tex = assetManager.loadTexture("Interface/Logo/Monkey.jpg");
+        tex.setWrap(Texture.WrapMode.Repeat);
+        mat.setTexture("DiffuseMap", tex);
+        floor.setMaterial(mat);
+        floor.rotate(-FastMath.HALF_PI, 0, 0);
+        rootNode.attachChild(floor);
+    }
+
+    /**
+     * Adds lights and filters
+     */
+    private void setupLights() {
+        viewPort.setBackgroundColor(ColorRGBA.DarkGray);
+        rootNode.setShadowMode(RenderQueue.ShadowMode.CastAndReceive);
+
+        AmbientLight ambient = new AmbientLight();
+        ambient.setColor(ColorRGBA.White);
+        //rootNode.addLight(ambient);
+
+        DirectionalLight sun = new DirectionalLight();
+        sun.setDirection((new Vector3f(-0.5f, -0.5f, -0.5f)).normalizeLocal());
+        sun.setColor(ColorRGBA.White);
+        rootNode.addLight(sun);
+
+        DirectionalLightShadowFilter dlsf = new DirectionalLightShadowFilter(assetManager, 4096, 3);
+        dlsf.setLight(sun);
+        dlsf.setShadowIntensity(0.4f);
+        dlsf.setShadowZExtend(256);
+
+        FXAAFilter fxaa = new FXAAFilter();
+        BloomFilter bloom = new BloomFilter(BloomFilter.GlowMode.Objects);
+
+        FilterPostProcessor fpp = new FilterPostProcessor(assetManager);
+        fpp.addFilter(bloom);
+        fpp.addFilter(dlsf);
+        fpp.addFilter(fxaa);
+        viewPort.addProcessor(fpp);
+    }
+
+    /**
+     * Creates a bitmap test used for displaying debug info.
+     */
+    private BitmapText createTextUI(ColorRGBA color, float xPos, float yPos) {
+        BitmapFont font = assetManager.loadFont("Interface/Fonts/Console.fnt");
+        BitmapText bmp = new BitmapText(font);
+        bmp.setSize(font.getCharSet().getRenderedSize());
+        bmp.setLocalTranslation(xPos, settings.getHeight() - yPos, 0);
+        bmp.setColor(color);
+        guiNode.attachChild(bmp);
+        return bmp;
+    }
+}