OpenGL ES 小試

since: 2012/03/09
update: 2012/03/09
reference: iPhone 3D Programming

A. 新增專案
      Xcode > File > New > Project... > iOS > Application >
      Empty Application > Next

       Product Name: HelloArrow
       Company Identifier: com.blogspot
       Device Family: iPhone
       Use Automatic Reference Counting: checked
       > Next > Create

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B. 新增 Framework
     新增以下的 Framework:
     OpenGLES, QuartzCore

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C. 新增 UIView 子類別
   Xcode > File > New > File...
    > iOS > Cocoa Touch > Objective-C class > Next
    Class: GLView
    Subclass of: UIView
    > Next > Create

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D. 開啓 GLView.h 檔案, 修改如下:
#import <UIKit/UIKit.h>
//@add
#import <OpenGLES/EAGL.h>
#import <QuartzCore/QuartzCore.h>
#import <OpenGLES/ES1/gl.h>
#import <OpenGLES/ES1/glext.h>

@interface GLView : UIView
{
    //@add
    EAGLContext *glContext;
}

//@add
@property (nonatomic, strong) EAGLContext *glContext;

//@add
- (void)drawView;

@end

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E. 開啓 GLView.m 檔案, 修改如下:

@implementation GLView

//@add
@synthesize glContext = _glContext;

//@add
- (EAGLContext *)glContext
{
    if (_glContext == nil) {
        _glContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES1];
    }
   
    return _glContext;
}

//@add: 覆寫 layerClass 方法(類似 typeof), 回傳一個 OpenGL Layer 的類別
+ (Class)layerClass
{
    return [CAEAGLLayer class];
}

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code
       
        //@add
        //      從 UIView 取得 layer (CALayer), 向下轉型成 CAEAGLLayer. 
        //      在此為安全的, 因為 layerClass 方法已被覆寫)
        CAEAGLLayer *eaglLayer = (CAEAGLLayer*) super.layer;

        // 直接使用 OpenGL 設定不透明度
        eaglLayer.opaque = YES;
       
        // 設定 Current Context
        [EAGLContext setCurrentContext:self.glContext];
       
        //@add: OpenGL 初始化
        // 定義:渲染(render)與幅(frame)緩衝區(buffer); GLuint 同義於 unsigned int
        GLuint framebuffer, renderbuffer;
       
        glGenFramebuffersOES(1, &framebuffer);
        glGenRenderbuffersOES(1, &renderbuffer);
        glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer);
        glBindRenderbufferOES(GL_RENDERBUFFER_OES, renderbuffer);
       
        [self.glContext renderbufferStorage:GL_RENDERBUFFER_OES fromDrawable:eaglLayer];

        glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER_OES, renderbuffer);
       
        // 建構一個對應的座標系統
        glViewport(0, 0, CGRectGetWidth(frame), CGRectGetHeight(frame));
       
        [self drawView];
    }
    return self;
}

//@add
- (void)drawView
{
    glClearColor(0.5f, 0.5f, 0.5f, 1); // 將顏色定義為灰色
    glClear(GL_COLOR_BUFFER_BIT); // 執行清除操作
   
    // 先將定義好的灰色填入緩衝區, 接著發佈到螢幕上
    [self.glContext presentRenderbuffer:GL_RENDERBUFFER_OES];
}

//@add
- (void)dealloc
{
    if ([EAGLContext currentContext] == self.glContext) {
        [EAGLContext setCurrentContext:nil];
    }
}

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F. 開啓 AppDelegate.h 檔案, 修改如下:
#import <UIKit/UIKit.h>
//@add
#import "GLView.h"

@interface AppDelegate : UIResponder <UIApplicationDelegate>
{
    //@add
    UIWindow *window;
    GLView *glView;
}

@property (strong, nonatomic) UIWindow *window;
//@add
@property (strong, nonatomic) GLView *glView;

@end

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G. 開啓 AppDelegate.m 檔案, 修改如下:
#import "AppDelegate.h"

@implementation AppDelegate

@synthesize window = _window;
//@add
@synthesize glView = _glView;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    /*
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;
    */
   
    //@update
    CGRect screenBounds = [[UIScreen mainScreen] bounds];   
    self.window = [[UIWindow alloc] initWithFrame:screenBounds];
    self.glView = [[GLView alloc] initWithFrame:screenBounds];
    [self.window addSubview:self.glView];
    [self.window makeKeyAndVisible];
   
    return YES;
}
....

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H. 隱藏狀態欄位
      開啓 HelloArrow-Info.plist 檔案, 新增一筆資料如下:
      Key: Status bar is initially hidden
      Value: YES

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I. 編譯並執行

    說明: 由於沒有設定 root view controller, 因此會出現以下的訊息:
               Application windows are expected to have a root view controller
               at the end of application launch