iOS 系统会通过一个称之为 Core Animation Compositor (核心动画合成器[系统组件])去控制最终在屏幕显示的图像。 --> 核心动画层可以同时拥有多个图层； --> 图层保存了所有的绘制结果； --> Core Animation Compositor 是由 OpenGL ES 来控制图形处理、图层的合成、帧缓存数据的快速交换； --> pixel color render buffer，是 Frame Buffers 与 Layers 交换数据的地方（共享）； --> other render buffers，是可选的，但一个 OpenGL ES 程序至少包含一个； --？-> 如果用 UIKit 直接做会怎样？ ----> Try It ... ViewController.view + UIImageView 前者，设置背景色为黑色； 后者，添加进前者中成为子控件； 1）后者直接设置 .image 为 一张白色的图片（自己要制作一张图片）； 2）后者不设置图片，设置颜色为白色，再 .layer 设置贝赛尔曲线进行剪切（要自己计算坐标，并进行绘制）； ---->
--？-> 使用 OpenGL ES 直接进行绘制？
首先，分析图像的组成：
背景色是纯黑色的；
图中有一个白色的直角三角形；
因为 OpenGL ES 实际绘制的图形是根据坐标点来进行填充的，而且三角形是由三个顶点连线组成的，所以 OpenGL ES 绘制的时候需要 三个坐标点； ----> Just Do It ... 类的绑定： 核心代码：
完整代码：
//// OpenGLES_Ch2_1ViewController.m// OpenGLES_Ch2_1//#import "OpenGLES_Ch2_1ViewController.h"@implementation OpenGLES_Ch2_1ViewController@synthesize baseEffect;/// This data type is used to store information for each vertextypedef struct { GLKVector3 positionCoords;}SceneVertex;/// Define vertex data for a triangle to use in examplestatic const SceneVertex vertices[] = { { {-0.5f, -0.5f, 0.0}}, // lower left corner { { 0.5f, -0.5f, 0.0}}, // lower right corner { {-0.5f, 0.5f, 0.0}}, // upper left corner};/// Called when the view controller's view is loaded// Perform initialization before the view is asked to draw- (void)viewDidLoad{ [super viewDidLoad]; // Verify the type of view created automatically by the // Interface Builder storyboard GLKView *view = (GLKView *)self.view; NSAssert([view isKindOfClass:[GLKView class]], @"View controller's view is not a GLKView"); // Create an OpenGL ES 2.0 context and provide it to the // view view.context = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2]; // Make the new context current [EAGLContext setCurrentContext:view.context]; // Create a base effect that provides standard OpenGL ES 2.0 // Shading Language programs and set constants to be used for // all subsequent rendering self.baseEffect = [[GLKBaseEffect alloc] init]; self.baseEffect.useConstantColor = GL_TRUE; self.baseEffect.constantColor = GLKVector4Make( 1.0f, // Red 1.0f, // Green 1.0f, // Blue 1.0f);// Alpha // Set the background color stored in the current context glClearColor(0.0f, 0.0f, 0.0f, 1.0f); // background color // Generate, bind, and initialize contents of a buffer to be // stored in GPU memory glGenBuffers(1, // STEP 1 &vertexBufferID); glBindBuffer(GL_ARRAY_BUFFER, // STEP 2 vertexBufferID); glBufferData( // STEP 3 GL_ARRAY_BUFFER, // Initialize buffer contents sizeof(vertices), // Number of bytes to copy vertices, // Address of bytes to copy GL_STATIC_DRAW); // Hint: cache in GPU memory}/// GLKView delegate method: Called by the view controller's view// whenever Cocoa Touch asks the view controller's view to// draw itself. (In this case, render into a frame buffer that// shares memory with a Core Animation Layer)- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect{ [self.baseEffect prepareToDraw]; // Clear Frame Buffer (erase previous drawing) glClear(GL_COLOR_BUFFER_BIT); // Enable use of positions from bound vertex buffer glEnableVertexAttribArray( // STEP 4 GLKVertexAttribPosition); glVertexAttribPointer( // STEP 5 GLKVertexAttribPosition, 3, // three components per vertex GL_FLOAT, // data is floating point GL_FALSE, // no fixed point scaling sizeof(SceneVertex), // no gaps in data NULL); // NULL tells GPU to start at // beginning of bound buffer // Draw triangles using the first three vertices in the // currently bound vertex buffer glDrawArrays(GL_TRIANGLES, // STEP 6 0, // Start with first vertex in currently bound buffer 3); // Use three vertices from currently bound buffer}/// Called when the view controller's view has been unloaded// Perform clean-up that is possible when you know the view // controller's view won't be asked to draw again soon.- (void)viewDidUnload{ [super viewDidUnload]; // Make the view's context current GLKView *view = (GLKView *)self.view; [EAGLContext setCurrentContext:view.context]; // Delete buffers that aren't needed when view is unloaded if (0 != vertexBufferID) { glDeleteBuffers (1, // STEP 7 &vertexBufferID); vertexBufferID = 0; } // Stop using the context created in -viewDidLoad ((GLKView *)self.view).context = nil; [EAGLContext setCurrentContext:nil];}@end复制代码