OpenglES学习4-立方体

这次我们参考xxx 实现的简单版本旋转立方体

- (void)prepare{
    // 1. 基本配置
    EAGLContext *ctx =  [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
    [EAGLContext setCurrentContext:ctx];
    self.ctx = ctx;
    
    glDeleteFramebuffers(1, &fboId);
    glDeleteBuffers(1, &colorRboId);
    glDeleteBuffers(1, &depthRboId);
    fboId = colorRboId = depthRboId = 0;
    
    glGenFramebuffers(1, &fboId);
    glBindFramebuffer(GL_FRAMEBUFFER, fboId);
    
    glGenRenderbuffers(1, &colorRboId);
    glBindRenderbuffer(GL_RENDERBUFFER, colorRboId);
    [self.ctx renderbufferStorage:GL_RENDERBUFFER fromDrawable:(CAEAGLLayer *)self.layer];
    GLint w,h;
    glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &w);
    glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &h);
    self.renderSize = CGSizeMake(w, h);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, colorRboId);
    [self chkFBOStatus];
    
    // --- depth render buffer
    glGenRenderbuffers(1, &depthRboId);
    glBindRenderbuffer(GL_RENDERBUFFER, depthRboId);
    //    Once a renderbuffer object is bound, we can specify the dimensions and format of the image stored in the renderbuffer.
    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, self.renderSize.width, self.renderSize.height);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthRboId);
    [self chkFBOStatus];

    // 2.
    glClearColor(0.423, 0.43, 0.87, 1);
    
    // 3. 设置顶点数据，下标数据
    glGenBuffers(1, &vboId);
    glBindBuffer(GL_ARRAY_BUFFER, vboId);
    //The vertex array data or element array data storage is created and initialized using the glBufferData command.
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
    
    // 3. shader配置
    [self setShader];
    
    projUnif = glGetUniformLocation(programId, "u_Projection");
    modelUnif = glGetUniformLocation(programId, "u_ModelView");
    
    // 5. 给shader 参数设置数据
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(VFVertex), (const GLvoid *)offsetof(VFVertex, position));
    glEnableVertexAttribArray(1);
    glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, sizeof(VFVertex), (const GLvoid *)offsetof(VFVertex, color));
}

- (void)drawAndRender{
    // 1. use program
    glUseProgram(programId);
    // 2. transform
    //FIXME: 这个不懂参数什么意思，如何取到的？
    self.modelPostion = GLKVector3Make(0, -0.5, -5);
    [self tansform];
    
    glViewport(0, 0, self.renderSize.width, self.renderSize.height);
    
    //FIXME: 这个不懂为什么设置？
    glDepthRangef(0, 1);
    // 3. clear old cached
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // 4. open depth test
    glEnable(GL_DEPTH_TEST);
    glEnable(GL_CULL_FACE);
    // 5. draw
    glBindRenderbuffer(GL_RENDERBUFFER, colorRboId);
    //The glBindBuffer command is used to make a buffer object the current array buffer object or the current element array buffer object.
//    glBindBuffer(GL_ARRAY_BUFFER, vboId);
    glDrawElements(GL_TRIANGLES, sizeof(indices)/sizeof(indices[0]), GL_UNSIGNED_BYTE, indices);
    
    // 6. render
    [self.ctx presentRenderbuffer:GL_RENDERBUFFER];
}

** 遗留的几个问题

1. 坐标空间的转换？

2. shader代码为何这么写？