九、OpenGL ES/Core Animation立方体贴图+旋转

1.OpenGL ES

1.1 透视投影

GLfloat vertexData[] = {
    0.5, -0.5, 0.0f,    1.0f, 0.0f, //右下
    0.5, 0.5,  0.0f,    1.0f, 1.0f, //右上
    -0.5, 0.5, 0.0f,    0.0f, 1.0f, //左上
    
    0.5, -0.5, 0.0f,    1.0f, 0.0f, //右下
    -0.5, 0.5, 0.0f,    0.0f, 1.0f, //左上
    -0.5, -0.5, 0.0f,   0.0f, 0.0f, //左下
};

虽然我们的代码看起来是绘制了一个正方形，但由于视口(视图)宽高比的问题产生了拉伸问题。如下图所示：

为了解决这个问题，我们可以设置透视投影矩阵。又由于平截头体可视范围的问题，我们需要将顶点向后移4.0单位。

CGFloat aspect = fabs(self.view.bounds.size.width / self.view.bounds.size.height);
GLKMatrix4 projectionMatrix = GLKMatrix4MakePerspective(GLKMathDegreesToRadians(65.0), aspect, 0.1, 100.0);
_baseEffect.transform.projectionMatrix = projectionMatrix;
    
GLKMatrix4 modelviewMatrix = GLKMatrix4Translate(GLKMatrix4Identity, 0, 0, -4.0);
_baseEffect.transform.modelviewMatrix = modelviewMatrix;

2.1 立方体贴图+旋转

解决了上面的问题，完成立方体贴图+旋转就很简单了。

• 写好立方体的顶点位置。
• - (void)glkView:(GLKView *)view drawInRect:(CGRect)rect 会不断回调，在里面更新模型视图变换矩阵就可以了。

OpenGL ES

@interface DemoViewController ()
{
    EAGLContext *_context;
    GLKBaseEffect *_baseEffect;
    int _angle;
}
@end

@implementation DemoViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    //1.OpenGL ES 相关初始化
    [self setUpConfig];
    //2.加载顶点/纹理坐标数据
    [self setUpVertexData];
    //3.加载纹理数据(使用GLBaseEffect)
    [self setUpTexture];
}

-(void)setUpTexture
{
    NSString *filePath = [[NSBundle mainBundle]pathForResource:@"qiyu" ofType:@"jpg"];
    
    NSDictionary *options = @{GLKTextureLoaderOriginBottomLeft : @(YES)};
    GLKTextureInfo *textureInfo = [GLKTextureLoader textureWithContentsOfFile:filePath options:options error:nil];
    // 纹理设置
    _baseEffect = [[GLKBaseEffect alloc] init];
    _baseEffect.texture2d0.enabled = GL_TRUE;
    _baseEffect.texture2d0.name = textureInfo.name;
    // 透视投影矩阵
    CGFloat aspect = fabs(self.view.bounds.size.width / self.view.bounds.size.height);
    GLKMatrix4 projectionMatrix = GLKMatrix4MakePerspective(GLKMathDegreesToRadians(65.0), aspect, 0.1, 100.0);
    _baseEffect.transform.projectionMatrix = projectionMatrix;
}

-(void)setUpVertexData
{
    GLfloat vertices[] = {
        -0.5f, -0.5f, -0.5f, 0.0f, 0.0f,
        0.5f, -0.5f, -0.5f, 1.0f, 0.0f,
        0.5f, 0.5f, -0.5f, 1.0f, 1.0f,
        0.5f, 0.5f, -0.5f, 1.0f, 1.0f,
        -0.5f, 0.5f, -0.5f, 0.0f, 1.0f,
        -0.5f, -0.5f, -0.5f, 0.0f, 0.0f,
        
        -0.5f, -0.5f, 0.5f, 0.0f, 0.0f,
        0.5f, -0.5f, 0.5f, 1.0f, 0.0f,
        0.5f, 0.5f, 0.5f, 1.0f, 1.0f,
        0.5f, 0.5f, 0.5f, 1.0f, 1.0f,
        -0.5f, 0.5f, 0.5f, 0.0f, 1.0f,
        -0.5f, -0.5f, 0.5f, 0.0f, 0.0f,
        
        -0.5f, 0.5f, 0.5f, 1.0f, 0.0f,
        -0.5f, 0.5f, -0.5f, 1.0f, 1.0f,
        -0.5f, -0.5f, -0.5f, 0.0f, 1.0f,
        -0.5f, -0.5f, -0.5f, 0.0f, 1.0f,
        -0.5f, -0.5f, 0.5f, 0.0f, 0.0f,
        -0.5f, 0.5f, 0.5f, 1.0f, 0.0f,
        
        0.5f, 0.5f, 0.5f, 1.0f, 0.0f,
        0.5f, 0.5f, -0.5f, 1.0f, 1.0f,
        0.5f, -0.5f, -0.5f, 0.0f, 1.0f,
        0.5f, -0.5f, -0.5f, 0.0f, 1.0f,
        0.5f, -0.5f, 0.5f, 0.0f, 0.0f,
        0.5f, 0.5f, 0.5f, 1.0f, 0.0f,
        
        -0.5f, -0.5f, -0.5f, 0.0f, 1.0f,
        0.5f, -0.5f, -0.5f, 1.0f, 1.0f,
        0.5f, -0.5f, 0.5f, 1.0f, 0.0f,
        0.5f, -0.5f, 0.5f, 1.0f, 0.0f,
        -0.5f, -0.5f, 0.5f, 0.0f, 0.0f,
        -0.5f, -0.5f, -0.5f, 0.0f, 1.0f,
        
        -0.5f, 0.5f, -0.5f, 0.0f, 1.0f,
        0.5f, 0.5f, -0.5f, 1.0f, 1.0f,
        0.5f, 0.5f, 0.5f, 1.0f, 0.0f,
        0.5f, 0.5f, 0.5f, 1.0f, 0.0f,
        -0.5f, 0.5f, 0.5f, 0.0f, 0.0f,
        -0.5f, 0.5f, -0.5f, 0.0f, 1.0f
    };
    // 顶点缓存
    GLuint bufferID;
    glGenBuffers(1, &bufferID);
    glBindBuffer(GL_ARRAY_BUFFER, bufferID);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    //顶点坐标数据
    glEnableVertexAttribArray(GLKVertexAttribPosition);
    glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 5, (GLfloat *)NULL + 0);
    //纹理坐标数据
    glEnableVertexAttribArray(GLKVertexAttribTexCoord0);
    glVertexAttribPointer(GLKVertexAttribTexCoord0, 2, GL_FLOAT, GL_FALSE, sizeof(GLfloat) * 5, (GLfloat *)NULL + 3);
}

- (void)setUpConfig
{
    _context = [[EAGLContext alloc]initWithAPI:kEAGLRenderingAPIOpenGLES3];
    if (!_context) {
        NSLog(@"Create ES context Failed");
    }
    //设置当前上下文
    [EAGLContext setCurrentContext:_context];
    
    GLKView *view =(GLKView *) self.view;
    view.context = _context;
    view.drawableColorFormat = GLKViewDrawableColorFormatRGBA8888;
    view.drawableDepthFormat = GLKViewDrawableDepthFormat16;
    
    glClearColor(0.8, 0.8, 0.8, 1.0);
}

#pragma mark -- GLKViewDelegate
- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect
{
    glEnable(GL_DEPTH_TEST);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    // 更新旋转
    [self update];
    [_baseEffect prepareToDraw];
    glDrawArrays(GL_TRIANGLES, 0, 48);
}

- (void)update {
    _angle = (_angle + 2) % 360;
    GLKMatrix4 modelviewMatrix = GLKMatrix4Translate(GLKMatrix4Identity, 0, 0, -4.0);
    modelviewMatrix = GLKMatrix4Rotate(modelviewMatrix, GLKMathDegreesToRadians(_angle), 0.3, 0.5, 0.7);
    _baseEffect.transform.modelviewMatrix = modelviewMatrix;
}

@end

2. Core Animation

使用 Core Animation 完成上面的功能也非常简单，利用layer.transform的数据结构CATransform3D即可完成3D变换。

值得一提的是，为了实现立方体整体的旋转动画，我们不需要为为一个面都专门做变换。我们只需要将它们放在同一个父视图中，利用父视图的layer.sublayerTransform即可对所有子视图进行统一变换。

Core Animation

@interface ViewController ()

@property (nonatomic, strong) UIView *containerView;

@end

@implementation ViewController

- (void)addFace:(int)index withTransform:(CATransform3D)transform
{
    NSString *filePath = [[NSBundle mainBundle]pathForResource:@"qiyu" ofType:@"jpg"];
    UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 200, 200)];
    imageView.image = [UIImage imageWithContentsOfFile:filePath];
    [self.containerView addSubview:imageView];
    CGSize containerSize = self.containerView.bounds.size;
    imageView.center = CGPointMake(containerSize.width / 2.0, containerSize.height / 2.0);
    // 变换
    imageView.layer.transform = transform;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = UIColor.lightGrayColor;
    
    self.containerView = [[UIView alloc] initWithFrame:self.view.bounds];
    [self.view addSubview:self.containerView];
    
    //add cube face 1
    CATransform3D transform = CATransform3DMakeTranslation(0, 0, 100);
    [self addFace:0 withTransform:transform];
    //add cube face 2
    transform = CATransform3DMakeTranslation(100, 0, 0);
    transform = CATransform3DRotate(transform, M_PI_2, 0, 1, 0);
    [self addFace:1 withTransform:transform];
    //add cube face 3
    transform = CATransform3DMakeTranslation(0, -100, 0);
    transform = CATransform3DRotate(transform, M_PI_2, 1, 0, 0);
    [self addFace:2 withTransform:transform];
    //add cube face 4
    transform = CATransform3DMakeTranslation(0, 100, 0);
    transform = CATransform3DRotate(transform, -M_PI_2, 1, 0, 0);
    [self addFace:3 withTransform:transform];
    //add cube face 5
    transform = CATransform3DMakeTranslation(-100, 0, 0);
    transform = CATransform3DRotate(transform, -M_PI_2, 0, 1, 0);
    [self addFace:4 withTransform:transform];
    //add cube face 6
    transform = CATransform3DMakeTranslation(0, 0, -100);
    transform = CATransform3DRotate(transform, M_PI, 0, 1, 0);
    [self addFace:5 withTransform:transform];
    
    __block int step = 0;
    NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:1.0/60.0 repeats:YES block:^(NSTimer * _Nonnull timer) {
        step = (step + 2) % 360;
        self.containerView.layer.sublayerTransform = CATransform3DMakeRotation(M_PI / 180.0 * step, -0.3, 0.5, -0.7);
    }];
    [[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
}

@end