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 vertex
typedef struct {
GLKVector3 positionCoords;
}
SceneVertex;
/////////////////////////////////////////////////////////////////
// Define vertex data for a triangle to use in example
static 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
