libgdx 3D 渲染优化

原文地址：http://blog.xoppa.com/3d-frustum-culling-with-libgdx/

非翻译，详细内容请见原文，捡点我能理解的说说吧~

关于矩阵之类的知识可以看一下 http://www.cppblog.com/lovedday/archive/2008/01/09/40813.html 我也不懂~~

渲染3D场景的时候，可见物件的数量要远远小于物件总数。

试想，在铺了一地地砖的时候，视角对着天，这时候需要渲染的地砖就没有了。摄像机照不到的地方，完全没有必要渲染。

只渲染可视视角范围内的物件，对于性能的提升是很大的。

直接上测试代码：

package com.mygdx.game;

import com.badlogic.gdx.ApplicationListener;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.assets.AssetManager;
import com.badlogic.gdx.graphics.Camera;
import com.badlogic.gdx.graphics.Color;
import com.badlogic.gdx.graphics.GL20;
import com.badlogic.gdx.graphics.PerspectiveCamera;
import com.badlogic.gdx.graphics.g2d.BitmapFont;
import com.badlogic.gdx.graphics.g3d.Environment;
import com.badlogic.gdx.graphics.g3d.Model;
import com.badlogic.gdx.graphics.g3d.ModelBatch;
import com.badlogic.gdx.graphics.g3d.ModelInstance;
import com.badlogic.gdx.graphics.g3d.attributes.ColorAttribute;
import com.badlogic.gdx.graphics.g3d.environment.DirectionalLight;
import com.badlogic.gdx.graphics.g3d.utils.CameraInputController;
import com.badlogic.gdx.math.Vector3;
import com.badlogic.gdx.math.collision.BoundingBox;
import com.badlogic.gdx.scenes.scene2d.Stage;
import com.badlogic.gdx.scenes.scene2d.ui.Label;
import com.badlogic.gdx.utils.Array;

/**
 * Created by HanHongmin on 14-7-24.
 */
public class FrustumCullingTestA implements ApplicationListener {
    protected PerspectiveCamera cam;
    protected CameraInputController camController;
    protected ModelBatch modelBatch;
    protected AssetManager assets;
    protected Array<ModelInstance> instances = new Array();
    protected Environment environment;
    protected boolean loading;

    protected Stage stage;
    protected Label label;
    protected BitmapFont font;
    protected StringBuilder stringBuilder;
    private Vector3 tempPosition = new Vector3();

    @Override
    public void create () {
        stage = new Stage();
        font = new BitmapFont();
        label = new Label(" ", new Label.LabelStyle(font, Color.WHITE));
        stage.addActor(label);
        stringBuilder = new StringBuilder();

        modelBatch = new ModelBatch();
        environment = new Environment();
        environment.set(new ColorAttribute(ColorAttribute.AmbientLight, 0.4f, 0.4f, 0.4f, 1f));
        environment.add(new DirectionalLight().set(0.8f, 0.8f, 0.8f, -1f, -0.8f, -0.2f));

        cam = new PerspectiveCamera(67, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
        cam.position.set(0f, 7f, 10f);
        cam.lookAt(0,0,0);
        cam.near = 1f;
        cam.far = 300f;
        cam.update();

        camController = new CameraInputController(cam);
        Gdx.input.setInputProcessor(camController);

        assets = new AssetManager();
        assets.load("data/box.g3db", Model.class);
        assets.load("data/box2.g3db", Model.class);
        loading = true;
    }

    private void doneLoading() {
        Model t1 = assets.get("data/box.g3db", Model.class);
        Model t2 = assets.get("data/box2.g3db", Model.class);

        for(int i=0;i<100;i++){
            for(int j=0;j<100;j++){
                Model t;
                if((i+j)%2==0){
                    t = t1;
                }else{
                    t=t2;
                }
                ModelInstance shipInstance = new ModelInstance(t);
                shipInstance.transform.setToTranslation(i, j, 0);//设置位置
                instances.add(shipInstance);
            }
        }

        loading = false;
    }

    private int visibleCount;
    @Override
    public void render () {
        if (loading && assets.update())
            doneLoading();
        camController.update();

        Gdx.gl.glViewport(0, 0, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
        Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT | GL20.GL_DEPTH_BUFFER_BIT);

        modelBatch.begin(cam);
        visibleCount = 0;
        for (final ModelInstance instance : instances) {
            if (isVisible(cam, instance)) {
                modelBatch.render(instance, environment);
                visibleCount++;
            }
        }
        modelBatch.end();

        stringBuilder.setLength(0);
        stringBuilder.append(" FPS: ").append(Gdx.graphics.getFramesPerSecond());
        stringBuilder.append(" Visible: ").append(visibleCount);
        label.setText(stringBuilder);
        stage.draw();
    }

    protected boolean isVisible(final Camera cam, final ModelInstance instance) {
        instance.transform.getTranslation(tempPosition);//把位置信息放到tempPosition中
        return cam.frustum.pointInFrustum(tempPosition);//frustum平截头体，表示的就是可视范围
    }

    @Override
    public void dispose () {
        modelBatch.dispose();
        instances.clear();
        assets.dispose();
    }

    @Override
    public void resize(int width, int height) {
        stage.getViewport().update(width, height, true);
    }

    @Override
    public void pause() {
    }

    @Override
    public void resume() {
    }
}

以上代码中，关键部分是isVisible函数，该函数中计算了物件位置是否是在可视范围内。

这种算法稍稍有点瑕疵，运行即可看出效果。如果一个物件的位置不在可视范围内，但是此物件有一角却在，常理来说是应该显示的，而实际却没有显示出来。

上代码吧：

package com.mygdx.game;

import com.badlogic.gdx.ApplicationListener;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.assets.AssetManager;
import com.badlogic.gdx.graphics.Camera;
import com.badlogic.gdx.graphics.Color;
import com.badlogic.gdx.graphics.GL20;
import com.badlogic.gdx.graphics.PerspectiveCamera;
import com.badlogic.gdx.graphics.g2d.BitmapFont;
import com.badlogic.gdx.graphics.g3d.Environment;
import com.badlogic.gdx.graphics.g3d.Model;
import com.badlogic.gdx.graphics.g3d.ModelBatch;
import com.badlogic.gdx.graphics.g3d.ModelInstance;
import com.badlogic.gdx.graphics.g3d.attributes.ColorAttribute;
import com.badlogic.gdx.graphics.g3d.environment.DirectionalLight;
import com.badlogic.gdx.graphics.g3d.utils.CameraInputController;
import com.badlogic.gdx.math.Vector3;
import com.badlogic.gdx.math.collision.BoundingBox;
import com.badlogic.gdx.scenes.scene2d.Stage;
import com.badlogic.gdx.scenes.scene2d.ui.Label;
import com.badlogic.gdx.utils.Array;

/**
 * Created by HanHongmin on 14-7-24.
 */
public class FrustumCullingTest implements ApplicationListener {
    protected PerspectiveCamera cam;
    protected CameraInputController camController;
    protected ModelBatch modelBatch;
    protected AssetManager assets;
    protected Array<GameObject> instances = new Array();
    protected Environment environment;
    protected boolean loading;

    protected Stage stage;
    protected Label label;
    protected BitmapFont font;
    protected StringBuilder stringBuilder;
    private Vector3 tempPosition = new Vector3();

    @Override
    public void create () {
        stage = new Stage();
        font = new BitmapFont();
        label = new Label(" ", new Label.LabelStyle(font, Color.WHITE));
        stage.addActor(label);
        stringBuilder = new StringBuilder();

        modelBatch = new ModelBatch();
        environment = new Environment();
        environment.set(new ColorAttribute(ColorAttribute.AmbientLight, 0.4f, 0.4f, 0.4f, 1f));
        environment.add(new DirectionalLight().set(0.8f, 0.8f, 0.8f, -1f, -0.8f, -0.2f));

        cam = new PerspectiveCamera(67, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
        cam.position.set(0f, 7f, 10f);
        cam.lookAt(0,0,0);
        cam.near = 1f;
        cam.far = 30f;//视角最远
        cam.update();

        camController = new CameraInputController(cam);
        Gdx.input.setInputProcessor(camController);

        assets = new AssetManager();
        assets.load("data/box.g3db", Model.class);
        assets.load("data/box2.g3db", Model.class);
        loading = true;
    }

    private void doneLoading() {
        Model t1 = assets.get("data/box.g3db", Model.class);
        Model t2 = assets.get("data/box2.g3db", Model.class);

        for(int i=0;i<100;i++){
            for(int j=0;j<100;j++){
                Model t;
                if((i+j)%2==0){
                    t = t1;
                }else{
                    t=t2;
                }
                GameObject shipInstance = new GameObject(t);
                shipInstance.transform.setToTranslation(i, j, 0);//设置位置
                instances.add(shipInstance);
            }
        }

        loading = false;
    }

    private int visibleCount;
    @Override
    public void render () {
        if (loading && assets.update())
            doneLoading();
        camController.update();

        Gdx.gl.glViewport(0, 0, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
        Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT | GL20.GL_DEPTH_BUFFER_BIT);

        modelBatch.begin(cam);
        visibleCount = 0;
        for (final GameObject instance : instances) {
            if (isVisible(cam, instance)) {
                modelBatch.render(instance, environment);
                visibleCount++;
            }
        }
        modelBatch.end();

        stringBuilder.setLength(0);
        stringBuilder.append(" FPS: ").append(Gdx.graphics.getFramesPerSecond());
        stringBuilder.append(" Visible: ").append(visibleCount);
        label.setText(stringBuilder);
        stage.draw();
    }

    protected boolean isVisible(final Camera cam, final GameObject instance) {
        instance.transform.getTranslation(tempPosition);
        tempPosition.add(instance.center);
        return cam.frustum.boundsInFrustum(tempPosition, instance.dimensions);
    }

    @Override
    public void dispose () {
        modelBatch.dispose();
        instances.clear();
        assets.dispose();
    }

    @Override
    public void resize(int width, int height) {
        stage.getViewport().update(width, height, true);
    }

    @Override
    public void pause() {
    }

    @Override
    public void resume() {
    }



    public static class GameObject extends ModelInstance {
        public final Vector3 center = new Vector3();
        public final Vector3 dimensions = new Vector3();

        private final static BoundingBox bounds = new BoundingBox();

        public GameObject(Model model) {
            super(model);
            calculateBoundingBox(bounds);
            center.set(bounds.getCenter());
            dimensions.set(bounds.getDimensions());
        }
    }
}

这个怎么算的，其实我想说：呵呵！我也不懂！！！谁整明白了请告诉我啊~

估计是看见一点就显示吧。反正是打到我们想要的效果了。

原文作者提到，当物件旋转时，可能会出现问题。贴一下原作最后的代码：

package com.mygdx.game;

import com.badlogic.gdx.ApplicationListener;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.assets.AssetManager;
import com.badlogic.gdx.graphics.Camera;
import com.badlogic.gdx.graphics.Color;
import com.badlogic.gdx.graphics.GL20;
import com.badlogic.gdx.graphics.PerspectiveCamera;
import com.badlogic.gdx.graphics.g2d.BitmapFont;
import com.badlogic.gdx.graphics.g3d.Environment;
import com.badlogic.gdx.graphics.g3d.Model;
import com.badlogic.gdx.graphics.g3d.ModelBatch;
import com.badlogic.gdx.graphics.g3d.ModelInstance;
import com.badlogic.gdx.graphics.g3d.attributes.ColorAttribute;
import com.badlogic.gdx.graphics.g3d.environment.DirectionalLight;
import com.badlogic.gdx.graphics.g3d.utils.CameraInputController;
import com.badlogic.gdx.math.Vector3;
import com.badlogic.gdx.math.collision.BoundingBox;
import com.badlogic.gdx.scenes.scene2d.Stage;
import com.badlogic.gdx.scenes.scene2d.ui.Label;
import com.badlogic.gdx.utils.Array;

/**
 * Created by HanHongmin on 14-7-24.
 */
public class FrustumCullingTestC implements ApplicationListener {
    protected PerspectiveCamera cam;
    protected CameraInputController camController;
    protected ModelBatch modelBatch;
    protected AssetManager assets;
    protected Array<GameObject> instances = new Array();
    protected Environment environment;
    protected boolean loading;

    protected Stage stage;
    protected Label label;
    protected BitmapFont font;
    protected StringBuilder stringBuilder;
    private Vector3 tempPosition = new Vector3();

    @Override
    public void create () {
        stage = new Stage();
        font = new BitmapFont();
        label = new Label(" ", new Label.LabelStyle(font, Color.WHITE));
        stage.addActor(label);
        stringBuilder = new StringBuilder();

        modelBatch = new ModelBatch();
        environment = new Environment();
        environment.set(new ColorAttribute(ColorAttribute.AmbientLight, 0.4f, 0.4f, 0.4f, 1f));
        environment.add(new DirectionalLight().set(0.8f, 0.8f, 0.8f, -1f, -0.8f, -0.2f));

        cam = new PerspectiveCamera(67, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
        cam.position.set(0f, 7f, 10f);
        cam.lookAt(0,0,0);
        cam.near = 1f;
        cam.far = 30f;//视角最远
        cam.update();

        camController = new CameraInputController(cam);
        Gdx.input.setInputProcessor(camController);

        assets = new AssetManager();
        assets.load("data/box.g3db", Model.class);
        assets.load("data/box2.g3db", Model.class);
        loading = true;
    }

    private void doneLoading() {
        Model t1 = assets.get("data/box.g3db", Model.class);
        Model t2 = assets.get("data/box2.g3db", Model.class);

        for(int i=0;i<100;i++){
            for(int j=0;j<100;j++){
                Model t;
                if((i+j)%2==0){
                    t = t1;
                }else{
                    t=t2;
                }
                GameObject shipInstance = new GameObject(t);
                shipInstance.transform.setToTranslation(i, j, 0);//设置位置
                instances.add(shipInstance);
            }
        }

        loading = false;
    }

    private int visibleCount;
    @Override
    public void render () {
        if (loading && assets.update())
            doneLoading();
        camController.update();

        Gdx.gl.glViewport(0, 0, Gdx.graphics.getWidth(), Gdx.graphics.getHeight());
        Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT | GL20.GL_DEPTH_BUFFER_BIT);

        modelBatch.begin(cam);
        visibleCount = 0;
        for (final GameObject instance : instances) {
            if (isVisible(cam, instance)) {
                modelBatch.render(instance, environment);
                visibleCount++;
            }
        }
        modelBatch.end();

        stringBuilder.setLength(0);
        stringBuilder.append(" FPS: ").append(Gdx.graphics.getFramesPerSecond());
        stringBuilder.append(" Visible: ").append(visibleCount);
        label.setText(stringBuilder);
        stage.draw();
    }

    protected boolean isVisible(final Camera cam, final GameObject instance) {
        instance.transform.getTranslation(tempPosition);
        tempPosition.add(instance.center);
        return cam.frustum.sphereInFrustum(tempPosition, instance.radius);
    }

    @Override
    public void dispose () {
        modelBatch.dispose();
        instances.clear();
        assets.dispose();
    }

    @Override
    public void resize(int width, int height) {
        stage.getViewport().update(width, height, true);
    }

    @Override
    public void pause() {
    }

    @Override
    public void resume() {
    }



    public static class GameObject extends ModelInstance {
        public final Vector3 center = new Vector3();
        public final Vector3 dimensions = new Vector3();
        public final float radius;

        private final static BoundingBox bounds = new BoundingBox();

        public GameObject(Model model) {
            super(model);
            calculateBoundingBox(bounds);
            center.set(bounds.getCenter());
            dimensions.set(bounds.getDimensions());
            radius = dimensions.len() / 2f;
        }
    }
}

注：以上代码我都有改过，比如GameObject的构造方法。会不会有问题我真不清楚。

另外还有两点：

1. Camera的far属性能够影响可视范围，不要忘了。

2. far边缘像是被刀切了一样，一条线，far越近越明显，是否有办法根据物件和摄像机位置再次筛选是否渲染呢？

far是一条直线，摄像机正对的中点看得更远一下可能更真实。