【Filament】绘制圆形

1 前言

​ Filament环境搭建中介绍了 Filament 的 Windows 和 Android 环境搭，绘制三角形中介绍了绘制纯色和彩色三角形，绘制矩形中介绍了绘制纯色和彩色矩形，本文将使用 Filament 绘制圆形。

2 绘制圆形

​ 本文项目结构如下，完整代码资源 → Filament绘制圆形。

2.1 自定义基类

​ 为方便读者将注意力聚焦在 Filament 的输入上，轻松配置复杂的环境依赖逻辑，笔者仿照 OpenGL ES 的写法，抽出了 FLSurfaceView 和 BaseModel 类。FLSurfaceView 与 GLSurfaceView 的功能类似，承载了渲染环境配置；BaseModel 中提供了一些 VertexBuffer、IndexBuffer、Material、Renderable 相关的工具类，方便子类直接使用这些工具类。

​ build.gradle

...
android {
    ...
    aaptOptions { // 在应用程序打包过程中不压缩的文件
        noCompress 'filamat', 'ktx'
    }
}

dependencies {
    implementation fileTree(dir: '../libs', include: ['*.aar'])
    ...
}

​ 说明：在项目根目录下的 libs 目录中，需要放入以下 aar 文件，它们源自Filament环境搭建中编译生成的 aar。

​ FLSurfaceView.java

package com.zhyan8.circle.filament;

import android.content.Context;
import android.graphics.Point;
import android.view.Choreographer;
import android.view.Surface;
import android.view.SurfaceView;

import com.google.android.filament.Camera;
import com.google.android.filament.Engine;
import com.google.android.filament.EntityManager;
import com.google.android.filament.Filament;
import com.google.android.filament.Renderer;
import com.google.android.filament.Scene;
import com.google.android.filament.Skybox;
import com.google.android.filament.SwapChain;
import com.google.android.filament.View;
import com.google.android.filament.Viewport;
import com.google.android.filament.android.DisplayHelper;
import com.google.android.filament.android.FilamentHelper;
import com.google.android.filament.android.UiHelper;

/*
 * Filament中待渲染的SurfaceView
 * 功能可以类比OpenGL ES中的GLSurfaceView
 * 用于创建Filament的渲染环境
 */
public class FLSurfaceView extends SurfaceView {
    public static int RENDERMODE_WHEN_DIRTY = 0; // 用户请求渲染才渲染一帧
    public static int RENDERMODE_CONTINUOUSLY = 1; // 持续渲染
    protected int mRenderMode = RENDERMODE_CONTINUOUSLY; // 渲染模式
    protected Choreographer mChoreographer; // 消息控制
    protected DisplayHelper mDisplayHelper; // 管理Display(可以监听分辨率或刷新率的变化)
    protected UiHelper mUiHelper; // 管理SurfaceView、TextureView、SurfaceHolder
    protected Engine mEngine; // 引擎(跟踪用户创建的资源, 管理渲染线程和硬件渲染器)
    protected Renderer mRenderer; // 渲染器(用于操作系统窗口, 生成绘制命令, 管理帧延时)
    protected Scene mScene; // 场景(管理渲染对象、灯光)
    protected View mView; // 存储渲染数据(View是Renderer操作的对象)
    protected Camera mCamera; // 相机(视角管理)
    protected Point mDesiredSize; // 渲染分辨率
    protected float[] mSkyboxColor; // 背景颜色
    protected SwapChain mSwapChain; // 操作系统的本地可渲染表面(native renderable surface, 通常是一个window或view)
    protected FrameCallback mFrameCallback = new FrameCallback(); // 帧回调

    static {
        Filament.init();
    }

    public FLSurfaceView(Context context) {
        super(context);
        mChoreographer = Choreographer.getInstance();
        mDisplayHelper = new DisplayHelper(context);
    }

    public void init() { // 初始化
        setupSurfaceView();
        setupFilament();
        setupView();
        setupScene();
    }

    public void setRenderMode(int renderMode) { // 设置渲染模式
        mRenderMode = renderMode;
    }

    public void requestRender() { // 请求渲染
        mChoreographer.postFrameCallback(mFrameCallback);
    }

    public void onResume() { // 恢复
        mChoreographer.postFrameCallback(mFrameCallback);
    }

    public void onPause() { // 暂停
        mChoreographer.removeFrameCallback(mFrameCallback);
    }

    public void onDestroy() { // 销毁Filament环境
        mChoreographer.removeFrameCallback(mFrameCallback);
        mUiHelper.detach();
        mEngine.destroyRenderer(mRenderer);
        mEngine.destroyView(mView);
        mEngine.destroyScene(mScene);
        mEngine.destroyCameraComponent(mCamera.getEntity());
        EntityManager entityManager = EntityManager.get();
        entityManager.destroy(mCamera.getEntity());
        mEngine.destroy();
    }

    protected void setupScene() { // 设置Scene参数
    }

    protected void onResized(int width, int height) { // Surface尺寸变化时回调
        double zoom = 1;
        double aspect = (double) width / (double) height;
        mCamera.setProjection(Camera.Projection.ORTHO,
                -aspect * zoom, aspect * zoom, -zoom, zoom, 0, 1000);
    }

    private void setupSurfaceView() { // 设置SurfaceView
        mUiHelper = new UiHelper(UiHelper.ContextErrorPolicy.DONT_CHECK);
        mUiHelper.setRenderCallback(new SurfaceCallback());
        if (mDesiredSize != null) {
            mUiHelper.setDesiredSize(mDesiredSize.x, mDesiredSize.y);
        }
        mUiHelper.attachTo(this);
    }

    private void setupFilament() { // 设置Filament参数
        mEngine = Engine.create();
        // mEngine = (new Engine.Builder()).featureLevel(Engine.FeatureLevel.FEATURE_LEVEL_0).build();
        mRenderer = mEngine.createRenderer();
        mScene = mEngine.createScene();
        mView = mEngine.createView();
        mCamera = mEngine.createCamera(mEngine.getEntityManager().create());
    }

    private void setupView() { // 设置View参数
        float[] color = mSkyboxColor != null ? mSkyboxColor : new float[] {0, 0, 0, 1};
        Skybox skybox = (new Skybox.Builder()).color(color).build(mEngine);
        mScene.setSkybox(skybox);
        if (mEngine.getActiveFeatureLevel() == Engine.FeatureLevel.FEATURE_LEVEL_0) {
            mView.setPostProcessingEnabled(false); // FEATURE_LEVEL_0不支持post-processing
        }
        mView.setCamera(mCamera);
        mView.setScene(mScene);
    }

    /*
     * 帧回调
     */
    private class FrameCallback implements Choreographer.FrameCallback {
        @Override
        public void doFrame(long frameTimeNanos) { // 渲染每帧数据
            if (mRenderMode == RENDERMODE_CONTINUOUSLY) {
                mChoreographer.postFrameCallback(this); // 请求下一帧
            }
            if (mUiHelper.isReadyToRender()) {
                if (mRenderer.beginFrame(mSwapChain, frameTimeNanos)) {
                    mRenderer.render(mView);
                    mRenderer.endFrame();
                }
            }
        }
    }

    /*
     * Surface回调
     */
    private class SurfaceCallback implements UiHelper.RendererCallback {
        @Override
        public void onNativeWindowChanged(Surface surface) { // Native窗口改变时回调
            if (mSwapChain != null) {
                mEngine.destroySwapChain(mSwapChain);
            }
            long flags = mUiHelper.getSwapChainFlags();
            if (mEngine.getActiveFeatureLevel() == Engine.FeatureLevel.FEATURE_LEVEL_0) {
                if (SwapChain.isSRGBSwapChainSupported(mEngine)) {
                    flags = flags | SwapChain.CONFIG_SRGB_COLORSPACE;
                }
            }
            mSwapChain = mEngine.createSwapChain(surface, flags);
            mDisplayHelper.attach(mRenderer, getDisplay());
        }

        @Override
        public void onDetachedFromSurface() { // 解绑Surface时回调
            mDisplayHelper.detach();
            if (mSwapChain != null) {
                mEngine.destroySwapChain(mSwapChain);
                mEngine.flushAndWait();
                mSwapChain = null;
            }
        }

        @Override
        public void onResized(int width, int height) { // Surface尺寸变化时回调
            mView.setViewport(new Viewport(0, 0, width, height));
            FilamentHelper.synchronizePendingFrames(mEngine);
            FLSurfaceView.this.onResized(width, height);
        }
    }
}

​ BaseModel.java

package com.zhyan8.circle.filament;

import android.content.res.AssetFileDescriptor;
import android.content.res.AssetManager;
import android.os.Handler;
import android.os.Looper;
import android.util.Log;

import com.google.android.filament.Box;
import com.google.android.filament.Engine;
import com.google.android.filament.EntityManager;
import com.google.android.filament.IndexBuffer;
import com.google.android.filament.Material;
import com.google.android.filament.MaterialInstance;
import com.google.android.filament.RenderableManager;
import com.google.android.filament.RenderableManager.PrimitiveType;
import com.google.android.filament.VertexBuffer;
import com.google.android.filament.VertexBuffer.AttributeType;
import com.google.android.filament.VertexBuffer.VertexAttribute;

import java.io.FileInputStream;
import java.io.IOException;
import java.nio.Buffer;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.channels.Channels;
import java.nio.channels.ReadableByteChannel;

/*
 * 模型基类
 * 管理模型的材质、顶点属性、顶点索引、渲染id
 */
public class BaseModel {
    private static String TAG = "BaseModel";
    protected AssetManager mAssetManager; // 资源管理器
    protected Engine mEngine; // Filament引擎
    protected Material mMaterial; // 模型材质
    protected MaterialInstance mMaterialInstance; // 模型材质实例
    protected VertexBuffer mVertexBuffer; // 顶点属性缓存
    protected IndexBuffer mIndexBuffer; // 顶点索引缓存
    protected int mRenderable; // 渲染id
    protected Box mBox; // 渲染区域

    public BaseModel(AssetManager assetManager, Engine engine) {
        mAssetManager = assetManager;
        mEngine = engine;
    }

    public Material getMaterial() { // 获取材质
        return mMaterial;
    }

    public VertexBuffer getVertexBuffer() { // 获取顶点属性缓存
        return mVertexBuffer;
    }

    public IndexBuffer getIndexBuffer() { // 获取顶点索引缓存
        return mIndexBuffer;
    }

    public int getRenderable() { // 获取渲染id
        return mRenderable;
    }

    public void destroy() { // 销毁模型
        mEngine.destroyEntity(mRenderable);
        mEngine.destroyVertexBuffer(mVertexBuffer);
        mEngine.destroyIndexBuffer(mIndexBuffer);
        mEngine.destroyMaterialInstance(mMaterialInstance);
        mEngine.destroyMaterial(mMaterial);
        EntityManager entityManager = EntityManager.get();
        entityManager.destroy(mRenderable);
    }

    protected Material loadMaterial(String materialPath) { // 加载材质
        Buffer buffer = readUncompressedAsset(mAssetManager, materialPath);
        if (buffer != null) {
            Material material = (new Material.Builder()).payload(buffer, buffer.remaining()).build(mEngine);
            mMaterialInstance = material.createInstance();
            material.compile(
                    Material.CompilerPriorityQueue.HIGH,
                    Material.UserVariantFilterBit.ALL,
                    new Handler(Looper.getMainLooper()),
                    () -> Log.i(TAG, "Material " + material.getName() + " compiled."));
            mEngine.flush();
            return material;
        }
        return null;
    }

    protected VertexBuffer getVertexBuffer(float[] values) { // 获取顶点属性缓存
        ByteBuffer vertexData = getByteBuffer(values);
        int vertexCount = values.length / 3;
        int vertexSize = Float.BYTES * 3;
        VertexBuffer vertexBuffer = new VertexBuffer.Builder()
                .bufferCount(1)
                .vertexCount(vertexCount)
                .attribute(VertexAttribute.POSITION, 0, AttributeType.FLOAT3, 0, vertexSize)
                .build(mEngine);
        vertexBuffer.setBufferAt(mEngine, 0, vertexData);
        return vertexBuffer;
    }

    protected VertexBuffer getVertexBuffer(Vertex[] values) { // 获取顶点属性缓存
        ByteBuffer vertexData = getByteBuffer(values);
        int vertexCount = values.length;
        int vertexSize = Vertex.BYTES;
        VertexBuffer vertexBuffer = new VertexBuffer.Builder()
                .bufferCount(1)
                .vertexCount(vertexCount)
                .attribute(VertexAttribute.POSITION, 0, AttributeType.FLOAT3, 0, vertexSize)
                .attribute(VertexAttribute.COLOR,    0, AttributeType.UBYTE4, 3 * Float.BYTES, vertexSize)
                .normalized(VertexAttribute.COLOR)
                .build(mEngine);
        vertexBuffer.setBufferAt(mEngine, 0, vertexData);
        return vertexBuffer;
    }

    protected IndexBuffer getIndexBuffer(short[] values) { // 获取顶点索引缓存
        ByteBuffer indexData = getByteBuffer(values);
        int indexCount = values.length;
        IndexBuffer indexBuffer = new IndexBuffer.Builder()
                .indexCount(indexCount)
                .bufferType(IndexBuffer.Builder.IndexType.USHORT)
                .build(mEngine);
        indexBuffer.setBuffer(mEngine, indexData);
        return indexBuffer;
    }

    protected int getRenderable(PrimitiveType primitiveType, int vertexCount) { // 获取渲染id
        int renderable = EntityManager.get().create();
        new RenderableManager.Builder(1)
                .boundingBox(mBox)
                .geometry(0, primitiveType, mVertexBuffer, mIndexBuffer, 0, vertexCount)
                .material(0, mMaterialInstance)
                .build(mEngine, renderable);
        return renderable;
    }

    private Buffer readUncompressedAsset(AssetManager assetManager, String assetPath) { // 加载资源
        ByteBuffer dist = null;
        try {
            AssetFileDescriptor fd = assetManager.openFd(assetPath);
            try(FileInputStream fis = fd.createInputStream()) {
                dist = ByteBuffer.allocate((int) fd.getLength());
                try (ReadableByteChannel src = Channels.newChannel(fis)) {
                    src.read(dist);
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        if (dist != null) {
            return dist.rewind();
        }
        return null;
    }

    private ByteBuffer getByteBuffer(float[] values) { // float数组转换为ByteBuffer
        ByteBuffer byteBuffer = ByteBuffer.allocate(values.length * Float.BYTES);
        byteBuffer.order(ByteOrder.nativeOrder());
        for (int i = 0; i < values.length; i++) {
            byteBuffer.putFloat(values[i]);
        }
        byteBuffer.flip();
        return byteBuffer;
    }

    private ByteBuffer getByteBuffer(short[] values) { // short数组转换为ByteBuffer
        ByteBuffer byteBuffer = ByteBuffer.allocate(values.length * Short.BYTES);
        byteBuffer.order(ByteOrder.nativeOrder());
        for (int i = 0; i < values.length; i++) {
            byteBuffer.putShort(values[i]);
        }
        byteBuffer.flip();
        return byteBuffer;
    }

    private ByteBuffer getByteBuffer(Vertex[] values) { // Vertex数组转换为ByteBuffer
        ByteBuffer byteBuffer = ByteBuffer.allocate(values.length * Vertex.BYTES);
        byteBuffer.order(ByteOrder.nativeOrder());
        for (int i = 0; i < values.length; i++) {
            values[i].put(byteBuffer);
        }
        byteBuffer.flip();
        return byteBuffer;
    }

    /*
     * 顶点数据
     * 包含顶点位置和颜色
     */
    public static class Vertex {
        public static int BYTES = 16;
        public float x;
        public float y;
        public float z;
        public int color;
        public Vertex() {}
        public Vertex(float x, float y, float z, int color) {
            this.x = x;
            this.y = y;
            this.z = z;
            this.color = color;
        }

        public ByteBuffer put(ByteBuffer buffer) { // Vertex转换为ByteBuffer
            buffer.putFloat(x);
            buffer.putFloat(y);
            buffer.putFloat(z);
            buffer.putInt(color);
            return buffer;
        }
    }
}

2.2 绘制纯色圆形（固定材质颜色）

​ MainActivity.java

package com.zhyan8.circle;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;

import com.zhyan8.circle.filament.FLSurfaceView;

public class MainActivity extends AppCompatActivity {
    private FLSurfaceView mFLSurfaceView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mFLSurfaceView = new MyFLSurfaceView(this);
        setContentView(mFLSurfaceView);
        mFLSurfaceView.init();
        mFLSurfaceView.setRenderMode(FLSurfaceView.RENDERMODE_CONTINUOUSLY);
    }

    @Override
    public void onResume() {
        super.onResume();
        mFLSurfaceView.onResume();
    }

    @Override
    public void onPause() {
        super.onPause();
        mFLSurfaceView.onPause();
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        mFLSurfaceView.onDestroy();
    }
}

​ MyFLSurfaceView.java

package com.zhyan8.circle;

import android.content.Context;

import com.google.android.filament.Camera;
import com.zhyan8.circle.filament.BaseModel;
import com.zhyan8.circle.filament.FLSurfaceView;

public class MyFLSurfaceView extends FLSurfaceView {
    private BaseModel mMyModel;
    public MyFLSurfaceView(Context context) {
        super(context);
    }

    public void init() {
        mSkyboxColor = new float[] {0.965f, 0.941f, 0.887f, 1};
        super.init();
    }

    @Override
    public void onDestroy() {
        mMyModel.destroy();
        super.onDestroy();
    }

    @Override
    protected void setupScene() { // 设置Scene参数
        mMyModel = new Circle1(getContext().getAssets(), mEngine);
        mScene.addEntity(mMyModel.getRenderable());
    }

    @Override
    protected void onResized(int width, int height) {
        double zoom = 1.5;
        double aspect = (double) width / (double) height;
        mCamera.setProjection(Camera.Projection.ORTHO,
                -aspect * zoom, aspect * zoom, -zoom, zoom, 0, 10);
    }
}

​ Circle1.java

package com.zhyan8.circle;

import android.content.res.AssetManager;

import com.google.android.filament.Box;
import com.google.android.filament.Engine;
import com.google.android.filament.RenderableManager.PrimitiveType;
import com.zhyan8.circle.filament.BaseModel;

public class Circle1 extends BaseModel {
    private String materialPath = "materials/circle1.filamat";
    private float[] mVertices;
    private short[] mIndex;

    public Circle1(AssetManager assetManager, Engine engine) {
        super(assetManager, engine);
        init();
    }

    private void init() {
        int num = 50;
        mVertices = getCircle(0, 0, 0.5f, num);
        mIndex = getIndices(num);
        mBox = new Box(0.0f, 0.0f, 0.0f, 1.0f, 1.0f, 0.01f);
        mMaterial = loadMaterial(materialPath);
        mVertexBuffer = getVertexBuffer(mVertices);
        mIndexBuffer = getIndexBuffer(mIndex);
        mRenderable = getRenderable(PrimitiveType.TRIANGLES, mIndex.length);
    }

    private float[] getCircle(float centerX, float centerY, float radius, int num) {
        float unit = (float) (2 * Math.PI / num);
        float[] coords = new float[(num + 1) * 3];
        int index = 0;
        for (int i = 0; i < num; i++) {
            coords[index++] = (float)(centerX + radius * Math.cos(unit * i));
            coords[index++] = (float)(centerY + radius * Math.sin(unit * i));
            coords[index++] = 0;
        }
        coords[index++] = centerX;
        coords[index++] = centerY;
        coords[index] = 0;
        return coords;
    }

    private short[] getIndices(int num) {
        short[] indices = new short[num * 3];
        short centerIndex = (short) num;
        short index = 0;
        for (short i = 0; i < num - 1; i++) {
            indices[index++] = centerIndex;
            indices[index++] = i;
            indices[index++] = (short)(i + 1);
        }
        indices[index++] = centerIndex;
        indices[index++] = (short) (num - 1);
        indices[index] = 0;
        return indices;
    }
}

​ circle1.mat

material {
    name : circle,

    // 禁用所有lighting
    shadingModel : unlit,
    featureLevel : 0
}

fragment {
    vec3 sRGB_to_linear(vec3 color) { // gamma解码, 转换到线下空间
        color.x = pow(color.r, 2.2);
        color.y = pow(color.g, 2.2);
        color.z = pow(color.b, 2.2);
        return color;
    }

    void material(inout MaterialInputs material) {
        prepareMaterial(material); // 在方法返回前必须回调该函数
        vec3 color = vec3(0.455, 0.725, 1.0);
        color = sRGB_to_linear(color);
        material.baseColor = vec4(color, 1.0);
    }
}

​ 说明：这里需要进行伽马解码处理，将颜色空间转换到线性空间中，否则显示的颜色将会偏亮，伽马编码原理详见 → 【Unity3D】伽马校正。

​ transform.bat

@echo off
setlocal enabledelayedexpansion
set "srcFolder=../src/main/materials"
set "distFolder=../src/main/assets/materials"

for %%f in ("%srcFolder%\*.mat") do (
	set "matfile=%%~nf"
	matc -p mobile -a opengl -o "!matfile!.filamat" "%%f"
    move "!matfile!.filamat" "%distFolder%\!matfile!.filamat"
)

echo Processing complete.
pause

​ 说明：需要将 matc.exe 文件与 transform.bat 文件放在同一个目录下面，matc.exe 源自Filament环境搭建中编译生成的 exe 文件。双击 transform.bat 文件，会自动将 /src/main/materials/ 下面的所有 mat 文件全部转换为 filamat 文件，并移到 /src/main/assets/materials/ 目录下面。

​ 运行效果如下。

2.3 绘制纯色圆形（传递材质颜色）

​ MyFLSurfaceView.java

package com.zhyan8.circle;

import android.content.Context;

import com.google.android.filament.Camera;
import com.zhyan8.circle.filament.BaseModel;
import com.zhyan8.circle.filament.FLSurfaceView;

public class MyFLSurfaceView extends FLSurfaceView {
    private BaseModel mMyModel;
    public MyFLSurfaceView(Context context) {
        super(context);
    }

    public void init() {
        mSkyboxColor = new float[] {0.965f, 0.941f, 0.887f, 1};
        super.init();
    }

    @Override
    public void onDestroy() {
        mMyModel.destroy();
        super.onDestroy();
    }

    @Override
    protected void setupScene() { // 设置Scene参数
        mMyModel = new Circle2(getContext().getAssets(), mEngine);
        mScene.addEntity(mMyModel.getRenderable());
    }

    @Override
    protected void onResized(int width, int height) {
        double zoom = 1.5;
        double aspect = (double) width / (double) height;
        mCamera.setProjection(Camera.Projection.ORTHO,
                -aspect * zoom, aspect * zoom, -zoom, zoom, 0, 10);
    }
}

​ Circle2.java

package com.zhyan8.circle;

import android.content.res.AssetManager;

import com.google.android.filament.Box;
import com.google.android.filament.Colors;
import com.google.android.filament.Engine;
import com.google.android.filament.RenderableManager.PrimitiveType;
import com.zhyan8.circle.filament.BaseModel;

public class Circle2 extends BaseModel {
    private String materialPath = "materials/circle2.filamat";
    private float[] mVertices;
    private short[] mIndex;

    public Circle2(AssetManager assetManager, Engine engine) {
        super(assetManager, engine);
        init();
    }

    private void init() {
        int num = 50;
        mVertices = getCircle(0, 0, 0.5f, num);
        mIndex = getIndices(num);
        mBox = new Box(0.0f, 0.0f, 0.0f, 1.0f, 1.0f, 0.01f);
        mMaterial = loadMaterial(materialPath);
        mMaterialInstance.setParameter("baseColor", Colors.RgbType.SRGB, 0.455f, 0.725f, 1.0f);
        mVertexBuffer = getVertexBuffer(mVertices);
        mIndexBuffer = getIndexBuffer(mIndex);
        mRenderable = getRenderable(PrimitiveType.TRIANGLES, mIndex.length);
    }

    private float[] getCircle(float centerX, float centerY, float radius, int num) {
        float unit = (float) (2 * Math.PI / num);
        float[] coords = new float[(num + 1) * 3];
        int index = 0;
        for (int i = 0; i < num; i++) {
            coords[index++] = (float)(centerX + radius * Math.cos(unit * i));
            coords[index++] = (float)(centerY + radius * Math.sin(unit * i));
            coords[index++] = 0;
        }
        coords[index++] = centerX;
        coords[index++] = centerY;
        coords[index] = 0;
        return coords;
    }

    private short[] getIndices(int num) {
        short[] indices = new short[num * 3];
        short centerIndex = (short) num;
        short index = 0;
        for (short i = 0; i < num - 1; i++) {
            indices[index++] = centerIndex;
            indices[index++] = i;
            indices[index++] = (short)(i + 1);
        }
        indices[index++] = centerIndex;
        indices[index++] = (short) (num - 1);
        indices[index] = 0;
        return indices;
    }
}

​ circle2.mat

material {
    name : circle,

    // 禁用所有lighting
    shadingModel : unlit,
    featureLevel : 0,
    parameters : [
        { // 颜色必须在线性空间中传递, 而不是sRGB空间
            type : float3,
            name : baseColor
        }
    ]
}

fragment {
    void material(inout MaterialInputs material) {
        prepareMaterial(material); // 在方法返回前必须回调该函数
        material.baseColor.rgb = materialParams.baseColor;
    }
}

​ 运行效果如下，可以看到，与 2.2 节中进行伽马校正后的颜色是一样的。

​ 声明：本文转自【Filament】绘制圆形。