Cocos2d-x3.2 下 OpenGL ES 2.0 第一个简单的实例画三角形

这里贴出具体的代码，比较简单。

HelloWorldScene.h

#ifndef __HELLOWORLD_SCENE_H__
#define __HELLOWORLD_SCENE_H__

#include "cocos2d.h"

class HelloWorld : public cocos2d::Layer
{
public:
    // there's no 'id' in cpp, so we recommend returning the class instance pointer
    static cocos2d::Scene* createScene();

    // Here's a difference. Method 'init' in cocos2d-x returns bool, instead of returning 'id' in cocos2d-iphone
    virtual bool init();  
    
    // implement the "static create()" method manually
    CREATE_FUNC(HelloWorld);
    
    
    
    virtual void visit(cocos2d::Renderer *renderer, const cocos2d::Mat4 &parentTransform, uint32_t parentFlags);
    
    void onDraw();
    
private:
    cocos2d::CustomCommand _command;
    
    
};

#endif // __HELLOWORLD_SCENE_H__

HelloWorldScene.cpp

#include "HelloWorldScene.h"

USING_NS_CC;

Scene* HelloWorld::createScene()
{
    // 'scene' is an autorelease object
    auto scene = Scene::create();
    
    // 'layer' is an autorelease object
    auto layer = HelloWorld::create();

    // add layer as a child to scene
    scene->addChild(layer);

    // return the scene
    return scene;
}

// on "init" you need to initialize your instance
bool HelloWorld::init()
{
    //////////////////////////////
    // 1. super init first
    if ( !Layer::init() )
    {
        return false;
    }
  

    this->setGLProgram(GLProgramCache::getInstance()->getGLProgram(GLProgram::SHADER_NAME_POSITION_COLOR));
        
    return true;
}

void HelloWorld::onDraw()
{
     //获得当前HelloWorld的shader
    auto glProgram = getGLProgram();
    //使用此shader
    glProgram->use();
    //设置该shader的一些内置uniform,主要是MVP，即model-view-project矩阵
    glProgram->setUniformsForBuiltins();
    
    auto size = Director::getInstance()->getWinSize();
    //指定将要绘制的三角形的三个顶点，分别位到屏幕左下角，右下角和正中间的顶端
    float vertercies[] = {0 , 0 , size.width , 0 , size.width / 2 , size.height};
    //指定每一个顶点的颜色，颜色值是RGBA格式的，取值范围是0-1
    float color[] = {0 , 0 , 1 , 1, //第一个点的颜色值蓝色
        1 , 0 , 0 ,1 ,              //第二个点的颜色值 红色
        0 , 1 , 0 , 1};             //第三个点的颜色值 绿色
    
    //激活名字为position和color的vertex attribute
    GL::enableVertexAttribs(GL::VERTEX_ATTRIB_FLAG_POSITION | GL::VERTEX_ATTRIB_FLAG_COLOR);
    //分别给position和color指定数据源
    glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_POSITION, 2, GL_FLOAT, GL_FALSE, 0, vertercies);
    
    glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_COLOR, 4, GL_FLOAT, GL_FALSE, 0, color);
    //绘制三角形，所谓的draw call就是指这个函数调用
    glDrawArrays(GL_TRIANGLES, 0, 3);
    //通知cocos2d-x 的renderer，让它在合适的时候调用这些OpenGL命令
    CC_INCREMENT_GL_DRAWN_BATCHES_AND_VERTICES(1, 3);
     //如果出错了，可以使用这个函数来获取出错信息
    CHECK_GL_ERROR_DEBUG();
    
    
    
    
    
}

void HelloWorld::visit(cocos2d::Renderer *renderer, const cocos2d::Mat4 &parentTransform, uint32_t parentFlags)
{
    Layer::visit(renderer, parentTransform, parentFlags);
    
    _command.init(_globalZOrder);
    _command.func = CC_CALLBACK_0(HelloWorld::onDraw, this);
    Director::getInstance()->getRenderer()->addCommand(&_command);
}