OpenGL ES实现AGLKView模仿GLKView
首先我们去创建这个一个AGLKView去继承自UIView类，然后我们进行自定义操作，主要就是去模仿GLKView中的定义
#import delegate;
//上下文
@property (nonatomic, strong) EAGLContext *context;
@property (nonatomic, readonly) NSInteger drawableWidth;
@property (nonatomic, readonly) NSInteger drawableHeight;
@property (nonatomic) AGLKViewDrawableDepthFormat
drawableDepthFormat;
- (instancetype)initWithFrame:(CGRect)frame context:(EAGLContext *)context;
- (void)display;
@end
#pragma mark - AGLKViewDelegate
//让AGLKView的代理对象实现渲染操作的方法
@protocol AGLKViewDelegate <NSObject>
@required
- (void)glkView:(AGLKView *)view drawInRect:(CGRect)rect;
AGLKView的实现方法
#import "AGLKView.h"
#import 之后我们再去自定义一个AGLKViewController类，这个类就是拿来模仿GLKViewController类的，很简单里面我们只需要去添加一个CADisplayLink定时器类和可以调节刷新的帧率就可以了。类定义如下所示
#import
{
CADisplayLink *displayLink;
NSInteger preferredFramesPerSecond;
}
/////////////////////////////////////////////////////////////////
// This property contains the desired frames per second rate for
// drawing. The default is 30.
@property (nonatomic) NSInteger preferredFramesPerSecond;
/////////////////////////////////////////////////////////////////
// This property contains the actual frames per second based
// upon the value for preferredFramesPerSecond property
// and the screen on which the GLKView resides.
// The value is as close to preferredFramesPerSecond as
// possible, without exceeding the screen's refresh rate. This
// value does not account for dropped frames, so it is not a
// measurement of your statistical frames per second. It is the
// static value for which updates will take place.
@property (nonatomic, readonly) NSInteger framesPerSecond;
/////////////////////////////////////////////////////////////////
// Thi property determines whether to pause or resume drawing
// at the rate defined by the framesPerSecond property.
// Initial value is NO.
@property (nonatomic, getter=isPaused) BOOL paused;
@end 类的实现
#import "AGLKViewController.h"
#import 接下来就用这两个类来实现画一个三角形，创建一个继承于AGLKViewController的类
类定义
#import "AGLKViewController.h"
#import 类的实现，其实主要就是设置顶点数据，传入顶点数据给顶点缓冲区，vertexBufferID这个是顶点缓冲区的标识符，然后再去实现- (void)glkView:(AGLKView *)view drawInRect:(CGRect)rect这个代理方法，然后进行绘制前的配置操作，比如说调用glClear清屏，以及设置允许使用绑定顶点缓存的位置，和设置数据格式调用glVertexAttribPointer方法，然后再调用glDrawArrays进行绘制
#import "OpenGLES_ViewController.h"
@implementation OpenGLES_Ch2_2ViewController
@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
AGLKView *view = (AGLKView *)self.view;
NSAssert([view isKindOfClass:[AGLKView class]],
@"View controller's view is not a AGLKView");
// Create an OpenGL ES 2.0 context and provide it to the
// view
//创建view的上下文
view.context = [[EAGLContext alloc]
initWithAPI:kEAGLRenderingAPIOpenGLES2];
// Make the new context current
//设置当前的上下文
[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
//创建basseffect对象
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:(AGLKView *)view drawInRect:(CGRect)rect
{
//准备绘制
[self.baseEffect prepareToDraw];
// Clear back 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];
// 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
((AGLKView *)self.view).context = nil;
[EAGLContext setCurrentContext:nil];
}
@end效果图，画出一个三角形
总结
- CAEAGLLayer是Core Animation提供的标准层类之一，CAEAGLLayer会与一个OpenGL ES的帧缓存共享它的像素颜色仓库
- 所有图形的ios应用都包含Core Animation层，所有的绘图都发生在层上。Core Animation合成器会混合当前应用与操作系统的层，从而会在OpenGL ES的后帧缓存中产生最终的像素颜色，之后Core Animation合成器切换前后缓存以便把合成的内存显示到屏幕上
- GLKBaseEffect类中隐藏了ios所支持的OpenGL ES版本之间的很多的不同，当我们使用OpenGL ES 2.0的时候，GLKBaseEffect会生成直接在GPU当中运行的Shading Language程序