安卓下多线程OpenGL共享Context (一)

    最近在研究Unity3D开发中使用Java Plugin进行纹理更新，想法很简单，在Java线程更新纹理数据，然后Unity场景中的纹理将自动更新。

首先，创建Java类，定义创建纹理及获取纹理参数的接口，并创建单线程池用于进行加载Bitmap并绑定纹理数据等OpenGL操作。Java代码示例：

package com.thornbirds.unity;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.opengl.GLES11Ext;
import android.opengl.GLES20;
import android.opengl.GLUtils;
import android.util.Log;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class PluginTexture {
    private static final String TAG = "PluginTexture";
    private int mTextureID = 0;
    private int mTextureWidth = 0;
    private int mTextureHeight = 0;

    // 创建单线程池，用于处理OpenGL纹理
    private final ExecutorService mRenderThread = Executors.newSingleThreadExecutor();

    public int getStreamTextureWidth() {
        return mTextureWidth;
    }

    public int getStreamTextureHeight() {
        return mTextureHeight;
    }

    public int getStreamTextureID() {
        return mTextureID;
    }

    public PluginTexture() {
    }

    public void setupOpenGL() {
        mRenderThread.execute(new Runnable() {
            @Override
            public void run() {
                // 生成OpenGL纹理ID
                int textures[] = new int[1];
                GLES20.glGenTextures(1, textures, 0);
                if (textures[0] == 0) {
                    Log.e(TAG, "glGenTextures failed");
                    return;
                }
                mTextureID = textures[0];
                mTextureWidth = 640;
                mTextureHeight = 360;
            }
        });
    }

    public void updateTexture() {
        mRenderThread.execute(new Runnable() {
            @Override
            public void run() {
                String imageFilePath = "/sdcard/test/image.png";
                final Bitmap bitmap = BitmapFactory.decodeFile(imageFilePath);

                GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, mTextureID);
                GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_MIN_FILTER, GLES20.GL_NEAREST);
                GLES20.glTexParameteri(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, GLES20.GL_TEXTURE_MAG_FILTER, GLES20.GL_NEAREST);
                GLUtils.texImage2D(GLES20.GL_TEXTURE_2D, 0, bitmap, 0);
                GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, 0);

                bitmap.recycle();
            }
        });
    }

    public void destroy() {
        mRenderThread.shutdownNow();
    }
}

    然后，创建C#脚本，在脚本中示例化Java对象，并调用Java方法初始化OpenGL；为了展示更新纹理，需获取到Java生成的纹理ID，并将其与脚本当前GameObject绑定。C#代码示例：

using System;
using UnityEngine;

public class PluginTestureDemo : MonoBehaviour {
    private AndroidJavaObject mPluginTexture; 
    private int mTextureId;
    private int mWidth;
    private int mHeight;

    void Start () {
        // 实例化com.thornbirds.unity.PluginTexture类的对象
        mPluginTexture = new AndroidJavaObject ("com.thornbirds.unity.PluginTexture");
        // 初始化OpenGL
        mPluginTexture.Call ("setupOpenGL");
    }

    void BindTexture () {
        // 获取JavaPlugin生成的纹理ID
        mTextureId = mPluginTexture.Call<int> ("getPluginTextureID");
        if (mTextureId == 0) {
            Debug.LogError ("getPluginTextureID failed");
            return;
        }
        mWidth = mPluginTexture.Call<int> ("getPluginTextureWidth");
        mHeight = mPluginTexture.Call<int> ("getPluginTextureHeight");
        // 将纹理ID与当前GameObject绑定
        GetComponent<MeshRenderer> ().material.mainTexture = Texture2D.CreateExternalTexture 
            (mWidth, mHeight, TextureFormat.ARGB32, false, false, (IntPtr) mTextureId);
        // 更新纹理数据
        mPluginTexture.Call ("updateTexture");
    }
}

注意：C#中使用了方法名调用Java方法，因此需要防止编译Jar包时Java类及其public方法被混淆。在Proguard文件中加入如下代码：

-keep class com.thornbirds.unity.PluginTexture {
    public *;
}

    该方案存在一个问题，在Java线程中访问进行OpenGL操作，会报Missing GLContext，需要为Java线程初始化OpenGL绘制环境。下回继续。