NDK OpenGLES 3.0 开发（一）：绘制一个三角形

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什么是 OpenGLES

OpenGLES 全称 OpenGL for Embedded Systems ，是三维图形应用程序接口 OpenGL 的子集，本质上是一个跨编程语言、跨平台的编程接口规范，主要应用于嵌入式设备，如手机、平板等。由科纳斯（Khronos）组织定义和推广，科纳斯是一个图形软硬件行业协会，该协会主要关注图形和多媒体方面的开放标准。

OpenGLES 3.0 的特点

OpenGLES 3.0 实际上是 OpenGLES 2.0 的扩展版本，向下兼容 OpenGLES 2.0 ，但不兼容 OpenGLES 1.0 。

OpenGLES 3.0 主要新特性

纹理

着色器

几何形状

缓冲区对象

帧缓冲区

OpenGLES 3.0 着色器语言规范变化

OpenGLES 3.0 着色器脚本

#version 300 es                          
layout(location = 0) in vec4 vPosition;  
void main()                              
{                                        
   gl_Position = vPosition;              
}

其中，#version 300 es 为 OpenGLES 3.0 版本声明，3.0 中使用 in 和 out 关键字取代 attribute 和 var**ying ，layout** 关键字直接为脚本中的属性指定位置，为属性赋值变成了：

GLfloat vVertices[] = {
            0.0f,  0.5f, 0.0f,
            -0.5f, -0.5f, 0.0f,
            0.5f, -0.5f, 0.0f,
            0.0f,  -1.0f, 0.0f,
            0.5f, -0.5f, 0.0f,
            -0.5f, -0.5f, 0.0f
    };

//第一个参数为对应属性的 location 值
glVertexAttribPointer (0, 3, GL_FLOAT, GL_FALSE, 0, vVertices );

而原来 2.0 的赋值方式为：

positionLoc = glGetAttribLocation（program, "vPosition"）;
glVertexAttribPointer(positionLoc, 3, GL_FLOAT, GL_FALSE, 0, vVertices );

绘制三角形

绘制一个三角形的步骤：

1. 创建 OpenGLES 环境（可以借助于 GLSurfaceView 创建的上下文对象）；

2. 编译并链接着色器程序；

3. 指定着色器程序，为着色器程序中的变量赋值；

4. 绘制。

基于 GLSurfaceView 搭建 OpenGLES 环境

简单自定义 GLSurfaceView。

package com.byteflow.app;

import android.content.Context;
import android.opengl.GLSurfaceView;
import android.util.AttributeSet;
import android.util.Log;
import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;

public class MyGLSurfaceView extends GLSurfaceView {
    private static final String TAG = "MyGLSurfaceView";

    public static final int IMAGE_FORMAT_RGBA = 0x01;
    public static final int IMAGE_FORMAT_NV21 = 0x02;
    public static final int IMAGE_FORMAT_NV12 = 0x03;
    public static final int IMAGE_FORMAT_I420 = 0x04;

    private MyGLRender mGLRender;
    private MyNativeRender mNativeRender;

    public MyGLSurfaceView(Context context) {
        this(context, null);
    }

    public MyGLSurfaceView(Context context, AttributeSet attrs) {
        super(context, attrs);
        this.setEGLContextClientVersion(3);
        mNativeRender = new MyNativeRender();
        mGLRender = new MyGLRender(mNativeRender);
        setRenderer(mGLRender);
        setRenderMode(RENDERMODE_CONTINUOUSLY);
    }

    public MyNativeRender getNativeRender() {
        return mNativeRender;
    }

    public static class MyGLRender implements GLSurfaceView.Renderer {
        private MyNativeRender mNativeRender;

        MyGLRender(MyNativeRender myNativeRender) {
            mNativeRender = myNativeRender;
        }

        @Override
        public void onSurfaceCreated(GL10 gl, EGLConfig config) {
            Log.d(TAG, "onSurfaceCreated() called with: gl = [" + gl + "], config = [" + config + "]");
            mNativeRender.native_OnSurfaceCreated();

        }

        @Override
        public void onSurfaceChanged(GL10 gl, int width, int height) {
            Log.d(TAG, "onSurfaceChanged() called with: gl = [" + gl + "], width = [" + width + "], height = [" + height + "]");
            mNativeRender.native_OnSurfaceChanged(width, height);

        }

        @Override
        public void onDrawFrame(GL10 gl) {
            Log.d(TAG, "onDrawFrame() called with: gl = [" + gl + "]");
            mNativeRender.native_OnDrawFrame();

        }
    }
}

JNI 类。

package com.byteflow.app;

public class MyNativeRender {
    static {
        System.loadLibrary("native-render");
    }

    public native void native_OnInit();

    public native void native_OnUnInit();

    public native void native_SetImageData(int format, int width, int height, byte[] bytes);

    public native void native_OnSurfaceCreated();

    public native void native_OnSurfaceChanged(int width, int height);

    public native void native_OnDrawFrame();
}

Native 层简单实现 JNI 。

//
// Created by ByteFlow on 2019/7/9.
//
#include "util/LogUtil.h"
#include <MyGLRenderContext.h>
#include "jni.h"

#define NATIVE_RENDER_CLASS_NAME "com/byteflow/app/MyNativeRender"

#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_byteflow_app_MyNativeRender
 * Method:    native_OnInit
 * Signature: ()V
 */
JNIEXPORT void JNICALL native_OnInit(JNIEnv *env, jobject instance)
{
    MyGLRenderContext::GetInstance();

}

/*
 * Class:     com_byteflow_app_MyNativeRender
 * Method:    native_OnUnInit
 * Signature: ()V
 */
JNIEXPORT void JNICALL native_OnUnInit(JNIEnv *env, jobject instance)
{
    MyGLRenderContext::DestroyInstance();
}

/*
 * Class:     com_byteflow_app_MyNativeRender
 * Method:    native_SetImageData
 * Signature: (III[B)V
 */
JNIEXPORT void JNICALL native_SetImageData
(JNIEnv *env, jobject instance, jint format, jint width, jint height, jbyteArray imageData)
{
    int len = env->GetArrayLength (imageData);
    uint8_t* buf = new uint8_t[len];
    env->GetByteArrayRegion(imageData, 0, len, reinterpret_cast<jbyte*>(buf));
    MyGLRenderContext::GetInstance()->SetImageData(format, width, height, buf);
    delete[] buf;
    env->DeleteLocalRef(imageData);
}

/*
 * Class:     com_byteflow_app_MyNativeRender
 * Method:    native_OnSurfaceCreated
 * Signature: ()V
 */
JNIEXPORT void JNICALL native_OnSurfaceCreated(JNIEnv *env, jobject instance)
{
    MyGLRenderContext::GetInstance()->OnSurfaceCreated();
}

/*
 * Class:     com_byteflow_app_MyNativeRender
 * Method:    native_OnSurfaceChanged
 * Signature: (II)V
 */
JNIEXPORT void JNICALL native_OnSurfaceChanged
(JNIEnv *env, jobject instance, jint width, jint height)
{
    MyGLRenderContext::GetInstance()->OnSurfaceChanged(width, height);

}

/*
 * Class:     com_byteflow_app_MyNativeRender
 * Method:    native_OnDrawFrame
 * Signature: ()V
 */
JNIEXPORT void JNICALL native_OnDrawFrame(JNIEnv *env, jobject instance)
{
    MyGLRenderContext::GetInstance()->OnDrawFrame();

}

#ifdef __cplusplus
}
#endif

static JNINativeMethod g_RenderMethods[] = {
        {"native_OnInit",             "()V",       (void *)(native_OnInit)},
        {"native_OnUnInit",           "()V",       (void *)(native_OnUnInit)},
        {"native_SetImageData",       "(III[B)V",  (void *)(native_SetImageData)},
        {"native_OnSurfaceCreated",   "()V",       (void *)(native_OnSurfaceCreated)},
        {"native_OnSurfaceChanged",   "(II)V",     (void *)(native_OnSurfaceChanged)},
        {"native_OnDrawFrame",        "()V",       (void *)(native_OnDrawFrame)},
};

static int RegisterNativeMethods(JNIEnv *env, const char *className, JNINativeMethod *methods, int methodNum)
{
    LOGCATE("RegisterNativeMethods");
    jclass clazz = env->FindClass(className);
    if (clazz == NULL)
    {
        LOGCATE("RegisterNativeMethods fail. clazz == NULL");
        return JNI_FALSE;
    }
    if (env->RegisterNatives(clazz, methods, methodNum) < 0)
    {
        LOGCATE("RegisterNativeMethods fail");
        return JNI_FALSE;
    }
    return JNI_TRUE;
}

static void UnregisterNativeMethods(JNIEnv *env, const char *className)
{
    LOGCATE("UnregisterNativeMethods");
    jclass clazz = env->FindClass(className);
    if (clazz == NULL)
    {
        LOGCATE("UnregisterNativeMethods fail. clazz == NULL");
        return;
    }
    if (env != NULL)
    {
        env->UnregisterNatives(clazz);
    }
}

// call this func when loading lib
extern "C" jint JNI_OnLoad(JavaVM *jvm, void *p)
{
    LOGCATE("===== JNI_OnLoad =====");
    jint jniRet = JNI_ERR;
    JNIEnv *env = NULL;
    if (jvm->GetEnv((void **) (&env), JNI_VERSION_1_6) != JNI_OK)
    {
        return jniRet;
    }

    jint regRet = RegisterNativeMethods(env, NATIVE_RENDER_CLASS_NAME, g_RenderMethods,
                                        sizeof(g_RenderMethods) /
                                        sizeof(g_RenderMethods[0]));
    if (regRet != JNI_TRUE)
    {
        return JNI_ERR;
    }

    return JNI_VERSION_1_6;
}

extern "C" void JNI_OnUnload(JavaVM *jvm, void *p)
{
    JNIEnv *env = NULL;
    if (jvm->GetEnv((void **) (&env), JNI_VERSION_1_6) != JNI_OK)
    {
        return;
    }

    UnregisterNativeMethods(env, NATIVE_RENDER_CLASS_NAME);
}

Native 层的 Render 封装类，其他的 Sample 都在此类中实现。

//
// Created by ByteFlow on 2019/7/9.
//

#include <TriangleSample.h>
#include "MyGLRenderContext.h"
#include "LogUtil.h"

MyGLRenderContext* MyGLRenderContext::m_pContext = nullptr;

MyGLRenderContext::MyGLRenderContext()
{

}

MyGLRenderContext::~MyGLRenderContext()
{

}

void MyGLRenderContext::SetImageData(int format, int width, int height, uint8_t *pData)
{
    LOGCATE("MyGLRenderContext::SetImageData format=%d, width=%d, height=%d, pData=%p", format, width, height, pData);
    NativeImage nativeImage;
    nativeImage.format = format;
    nativeImage.width = width;
    nativeImage.height = height;
    nativeImage.ppPlane[0] = pData;

    switch (format)
    {
        case IMAGE_FORMAT_NV12:
        case IMAGE_FORMAT_NV21:
            nativeImage.ppPlane[1] = nativeImage.ppPlane[0] + width * height;
            break;
        case IMAGE_FORMAT_I420:
            nativeImage.ppPlane[1] = nativeImage.ppPlane[0] + width * height;
            nativeImage.ppPlane[2] = nativeImage.ppPlane[1] + width * height / 4;
            break;
        default:
            break;
    }

    //m_TextureMapSample->LoadImage(&nativeImage);

}

void MyGLRenderContext::OnSurfaceCreated()
{
    LOGCATE("MyGLRenderContext::OnSurfaceCreated");
    glClearColor(1.0f,1.0f,0.5f, 1.0f);
    m_Sample.Init();
}

void MyGLRenderContext::OnSurfaceChanged(int width, int height)
{
    LOGCATE("MyGLRenderContext::OnSurfaceChanged [w, h] = [%d, %d]", width, height);
    glViewport(0, 0, width, height);
}

void MyGLRenderContext::OnDrawFrame()
{
    LOGCATE("MyGLRenderContext::OnDrawFrame");
    glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);

    m_Sample.Draw();


}

MyGLRenderContext *MyGLRenderContext::GetInstance()
{
    LOGCATE("MyGLRenderContext::GetInstance");
    if (m_pContext == nullptr)
    {
        m_pContext = new MyGLRenderContext();
    }
    return m_pContext;
}

void MyGLRenderContext::DestroyInstance()
{
    LOGCATE("MyGLRenderContext::DestroyInstance");
    if (m_pContext)
    {
        delete m_pContext;
        m_pContext = nullptr;
    }

}

编译链接着色器程序，进行绘制

三角形的绘制实现类。

//
// Created by ByteFlow on 2019/7/9.
//

#include "TriangleSample.h"
#include "../util/GLUtils.h"
#include "../util/LogUtil.h"

TriangleSample::TriangleSample()
{

}

TriangleSample::~TriangleSample()
{
    if (m_ProgramObj)
    {
        glDeleteProgram(m_ProgramObj);
    }

}

void TriangleSample::Init()
{
    char vShaderStr[] =
            "#version 300 es                          \n"
            "layout(location = 0) in vec4 vPosition;  \n"
            "void main()                              \n"
            "{                                        \n"
            "   gl_Position = vPosition;              \n"
            "}                                        \n";

    char fShaderStr[] =
            "#version 300 es                              \n"
            "precision mediump float;                     \n"
            "out vec4 fragColor;                          \n"
            "void main()                                  \n"
            "{                                            \n"
            "   fragColor = vec4 ( 1.0, 0.0, 0.0, 1.0 );  \n"
            "}                                            \n";

    m_ProgramObj = GLUtils::CreateProgram(vShaderStr, fShaderStr, m_VertexShader, m_FragmentShader);

}

void TriangleSample::Draw()
{
    LOGCATE("TriangleSample::Draw");
    GLfloat vVertices[] = {
            0.0f,  0.5f, 0.0f,
            -0.5f, -0.5f, 0.0f,
            0.5f, -0.5f, 0.0f,
    };

    if(m_ProgramObj == 0)
        return;

    // Use the program object
    glUseProgram (m_ProgramObj);

    // Load the vertex data
    glVertexAttribPointer (0, 3, GL_FLOAT, GL_FALSE, 0, vVertices );
    glEnableVertexAttribArray (0);

    glDrawArrays (GL_TRIANGLES, 0, 3);

}

编译和链接着色器程序的类

#include "GLUtils.h"
#include "LogUtil.h"
#include <stdlib.h>

GLuint GLUtils::LoadShader(GLenum shaderType, const char *pSource)
{
    GLuint shader = 0;
        shader = glCreateShader(shaderType);
        if (shader)
        {
            glShaderSource(shader, 1, &pSource, NULL);
            glCompileShader(shader);
            GLint compiled = 0;
            glGetShaderiv(shader, GL_COMPILE_STATUS, &compiled);
            if (!compiled)
            {
                GLint infoLen = 0;
                glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &infoLen);
                if (infoLen)
                {
                    char* buf = (char*) malloc((size_t)infoLen);
                    if (buf)
                    {
                        glGetShaderInfoLog(shader, infoLen, NULL, buf);
                        LOGCATE("GLUtils::LoadShader Could not compile shader %d:\n%s\n", shaderType, buf);
                        free(buf);
                    }
                    glDeleteShader(shader);
                    shader = 0;
                }
            }
        }
    return shader;
}

GLuint GLUtils::CreateProgram(const char *pVertexShaderSource, const char *pFragShaderSource, GLuint &vertexShaderHandle, GLuint &fragShaderHandle)
{
    GLuint program = 0;
        vertexShaderHandle = LoadShader(GL_VERTEX_SHADER, pVertexShaderSource);
        if (!vertexShaderHandle) return program;

        fragShaderHandle = LoadShader(GL_FRAGMENT_SHADER, pFragShaderSource);
        if (!fragShaderHandle) return program;

        program = glCreateProgram();
        if (program)
        {
            glAttachShader(program, vertexShaderHandle);
            CheckGLError("glAttachShader");
            glAttachShader(program, fragShaderHandle);
            CheckGLError("glAttachShader");
            glLinkProgram(program);
            GLint linkStatus = GL_FALSE;
            glGetProgramiv(program, GL_LINK_STATUS, &linkStatus);

            glDetachShader(program, vertexShaderHandle);
            glDeleteShader(vertexShaderHandle);
            vertexShaderHandle = 0;
            glDetachShader(program, fragShaderHandle);
            glDeleteShader(fragShaderHandle);
            fragShaderHandle = 0;
            if (linkStatus != GL_TRUE)
            {
                GLint bufLength = 0;
                glGetProgramiv(program, GL_INFO_LOG_LENGTH, &bufLength);
                if (bufLength)
                {
                    char* buf = (char*) malloc((size_t)bufLength);
                    if (buf)
                    {
                        glGetProgramInfoLog(program, bufLength, NULL, buf);
                        LOGCATE("GLUtils::CreateProgram Could not link program:\n%s\n", buf);
                        free(buf);
                    }
                }
                glDeleteProgram(program);
                program = 0;
            }
        }
    LOGCATE("GLUtils::CreateProgram program = %d", program);
    return program;
}

void GLUtils::DeleteProgram(GLuint &program)
{
    LOGCATE("GLUtils::DeleteProgram");
    if (program)
    {
        glUseProgram(0);
        glDeleteProgram(program);
        program = 0;
    }
}

void GLUtils::CheckGLError(const char *pGLOperation)
{
    for (GLint error = glGetError(); error; error = glGetError())
    {
        LOGCATE("GLUtils::CheckGLError GL Operation %s() glError (0x%x)\n", pGLOperation, error);
    }

}

在 Init 函数中实现编译链接着色器程序 m_ProgramObj ，其中顶点着色器脚本：

#version 300 es                          
layout(location = 0) in vec4 vPosition;  
void main()                              
{                                        
   gl_Position = vPosition;              
}

片元着色器脚本：

#version 300 es                              
precision mediump float;                     
out vec4 fragColor;                          
void main()                                  
{                                            
   fragColor = vec4 ( 1.0, 0.0, 0.0, 1.0 );  //填充三角形区域为红色
}

在 Draw 函数中指定着色器程序，为着色器程序中的变量赋值，传入顶点坐标信息，然后绘制三角形。

opengles 坐标系中三角形顶点坐标

绘制的结果图

参考

OpenGLES 维基百科

https://zh.wikipedia.org/wiki/OpenGL_ES

OpenGLES 3.0 编程指南

https://book.douban.com/subject/26414014/

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