OpenGL/OpenGL ES (六) —— 立方体旋转

OpenGL/OpenGL ES (一) —— 专业名词快速了解
OpenGL/OpenGL ES (二) —— 渲染架构、图元、着色器、投影
OpenGL/OpenGL ES (三) —— 绘制甜甜圈
OpenGL/OpenGL ES (四) —— 纹理
OpenGL/OpenGL ES (五) —— 纹理翻转策略
OpenGL/OpenGL ES (六) —— 立方体旋转
OpenGL/OpenGL ES (七) —— 初探
OpenGL/OpenGL ES (八) —— 如何加载一张图片
OpenGL/OpenGL ES (九) —— 光照

前言

先看下大致的效果一个正立体围绕Z轴旋转，可以自行修改旋转的轴，只要在update方法中修改相对应的x、y、z、坐标就OK了。

最终效果.png

第一步

1、初始化一个 EAGLContext画布，通过画布初始化一个GLKView视图并且设置相对应的属性 。加载纹理属性GLKTextureInfo设置到GLKBaseEffect对象上。

- (void)commonInit {
   
    //1.创建context
     EAGLContext *context = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES3];
    //设置当前context
    [EAGLContext setCurrentContext:context];
    
    //2.创建GLKView并设置代理
    CGRect frame = CGRectMake(0, 100, self.view.frame.size.width, self.view.frame.size.width);
    self.glkView = [[GLKView alloc] initWithFrame:frame context:context];
    self.glkView.backgroundColor = [UIColor clearColor];
    self.glkView.delegate = self;
    
    //3.使用深度缓存
    self.glkView.drawableDepthFormat = GLKViewDrawableDepthFormat24;
    //默认是(0, 1)，这里用于翻转 z 轴，使正方形朝屏幕外
    //glDepthRangef(1, 0);
    
    //4.将GLKView 添加self.view 上
    [self.view addSubview:self.glkView];

    //5.获取纹理图片
    NSString *imagePath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"image.png"];
    UIImage *image = [UIImage imageWithContentsOfFile:imagePath];
    
    //6.设置纹理参数
    NSDictionary *options = @{GLKTextureLoaderOriginBottomLeft : @(YES)};
    GLKTextureInfo *textureInfo = [GLKTextureLoader textureWithCGImage:[image CGImage]
                                                               options:options
                                                                 error:NULL];
  
    //7.使用baseEffect
    self.baseEffect = [[GLKBaseEffect alloc] init];
    self.baseEffect.texture2d0.name = textureInfo.name;
    self.baseEffect.texture2d0.target = textureInfo.target;

}

第二步

1、加载顶点和纹理坐标数据

- (void)vertexDataSetup {
    /*
     解释一下:
     这里我们不复用顶点，使用每 3 个点画一个三角形的方式，需要 12 个三角形，则需要 36 个顶点
     以下的数据用来绘制以（0，0，0）为中心，边长为 1 的立方体
     */
    
    //8. 开辟顶点数据空间(数据结构SenceVertex 大小 * 顶点个数kCoordCount)
    self.vertices = malloc(sizeof(CCVertex) * kCoordCount);
    
    // 前面
    self.vertices[0] = (CCVertex){{-0.5, 0.5, 0.5},  {0, 1}};
    self.vertices[1] = (CCVertex){{-0.5, -0.5, 0.5}, {0, 0}};
    self.vertices[2] = (CCVertex){{0.5, 0.5, 0.5},   {1, 1}};
    
    self.vertices[3] = (CCVertex){{-0.5, -0.5, 0.5}, {0, 0}};
    self.vertices[4] = (CCVertex){{0.5, 0.5, 0.5},   {1, 1}};
    self.vertices[5] = (CCVertex){{0.5, -0.5, 0.5},  {1, 0}};
    
    // 上面
    self.vertices[6] = (CCVertex){{0.5, 0.5, 0.5},    {1, 1}};
    self.vertices[7] = (CCVertex){{-0.5, 0.5, 0.5},   {0, 1}};
    self.vertices[8] = (CCVertex){{0.5, 0.5, -0.5},   {1, 0}};
    self.vertices[9] = (CCVertex){{-0.5, 0.5, 0.5},   {0, 1}};
    self.vertices[10] = (CCVertex){{0.5, 0.5, -0.5},  {1, 0}};
    self.vertices[11] = (CCVertex){{-0.5, 0.5, -0.5}, {0, 0}};
    
    // 下面
    self.vertices[12] = (CCVertex){{0.5, -0.5, 0.5},    {1, 1}};
    self.vertices[13] = (CCVertex){{-0.5, -0.5, 0.5},   {0, 1}};
    self.vertices[14] = (CCVertex){{0.5, -0.5, -0.5},   {1, 0}};
    self.vertices[15] = (CCVertex){{-0.5, -0.5, 0.5},   {0, 1}};
    self.vertices[16] = (CCVertex){{0.5, -0.5, -0.5},   {1, 0}};
    self.vertices[17] = (CCVertex){{-0.5, -0.5, -0.5},  {0, 0}};
    
    // 左面
    self.vertices[18] = (CCVertex){{-0.5, 0.5, 0.5},    {1, 1}};
    self.vertices[19] = (CCVertex){{-0.5, -0.5, 0.5},   {0, 1}};
    self.vertices[20] = (CCVertex){{-0.5, 0.5, -0.5},   {1, 0}};
    self.vertices[21] = (CCVertex){{-0.5, -0.5, 0.5},   {0, 1}};
    self.vertices[22] = (CCVertex){{-0.5, 0.5, -0.5},   {1, 0}};
    self.vertices[23] = (CCVertex){{-0.5, -0.5, -0.5},  {0, 0}};
    
    // 右面
    self.vertices[24] = (CCVertex){{0.5, 0.5, 0.5},    {1, 1}};
    self.vertices[25] = (CCVertex){{0.5, -0.5, 0.5},   {0, 1}};
    self.vertices[26] = (CCVertex){{0.5, 0.5, -0.5},   {1, 0}};
    self.vertices[27] = (CCVertex){{0.5, -0.5, 0.5},   {0, 1}};
    self.vertices[28] = (CCVertex){{0.5, 0.5, -0.5},   {1, 0}};
    self.vertices[29] = (CCVertex){{0.5, -0.5, -0.5},  {0, 0}};
    
    // 后面
    self.vertices[30] = (CCVertex){{-0.5, 0.5, -0.5},   {0, 1}};
    self.vertices[31] = (CCVertex){{-0.5, -0.5, -0.5},  {0, 0}};
    self.vertices[32] = (CCVertex){{0.5, 0.5, -0.5},    {1, 1}};
    self.vertices[33] = (CCVertex){{-0.5, -0.5, -0.5},  {0, 0}};
    self.vertices[34] = (CCVertex){{0.5, 0.5, -0.5},    {1, 1}};
    self.vertices[35] = (CCVertex){{0.5, -0.5, -0.5},   {1, 0}};
    
    //开辟缓存区 VBO
    glGenBuffers(1, &_vertexBuffer);
    glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
    GLsizeiptr bufferSizeBytes = sizeof(CCVertex) * kCoordCount;
    glBufferData(GL_ARRAY_BUFFER, bufferSizeBytes, self.vertices, GL_STATIC_DRAW);
    
    //顶点数据
    glEnableVertexAttribArray(GLKVertexAttribPosition);
    glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, sizeof(CCVertex), NULL + offsetof(CCVertex, positionCoord));
    
    //纹理数据
    glEnableVertexAttribArray(GLKVertexAttribTexCoord0);
    glVertexAttribPointer(GLKVertexAttribTexCoord0, 2, GL_FLOAT, GL_FALSE, sizeof(CCVertex), NULL + offsetof(CCVertex, textureCoord));
    
}

第三步

1、在GLKViewDelegate方法中开启深度测试，开始准备绘制，调用 glDrawArrays()进行绘制。

#pragma mark - GLKViewDelegate
- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect  {
    
    //1.开启深度测试
    glEnable(GL_DEPTH_TEST);
    //2.清除颜色缓存区&深度缓存区
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    //3.准备绘制
    [self.baseEffect prepareToDraw];
    
    //4.绘图
    glDrawArrays(GL_TRIANGLES, 0, kCoordCount);
}

第四步

1、添加定时器让它不断的去刷新绘制

- (void) addCADisplayLink {
       self.angle = 0;
    self.displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(update)];
    [self.displayLink addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];
}

第五步

1、设置旋转度数，设置旋转轴为Z轴，重新刷新绘制。

- (void)update {
   
    //1.计算旋转度数
    self.angle = (self.angle + 5) % 360;

    //2.修改baseEffect.transform.modelviewMatrix
    //进行图像旋转`GLKMathDegreesToRadians`度数转弧度
    self.baseEffect.transform.modelviewMatrix = GLKMatrix4MakeRotation(GLKMathDegreesToRadians(self.angle), 0, 0, 1);
    //3.重新渲染
    [self.glkView display];
}