#import <UIKit/UIKit.h>
#import <OpenGLES/EAGL.h>
#import <OpenGLES/ES1/gl.h>
#import <OpenGLES/ES1/glext.h>

@interface EAGLView : UIView {
    
@private
    // 백버퍼의 넓이, 높이 
    GLint backingWidth;
    GLint backingHeight;
    
    EAGLContext *context;
   
 // 렌더버퍼, 프레임버퍼 식별자
    GLuint viewRenderbuffer, viewFramebuffer;
    
   // 깊이 버퍼, 사용하지 않으면 0
    GLuint depthRenderbuffer;
}

- (void)beginDraw;
- (void)finishDraw;
- (void)setupViewLandscape;
- (void)setupViewPortrait;

+ (Class)layerClass {
    return [CAEAGLLayer class];
}

- (id)initWithFrame:(CGRect)rect {
    
    if ((self = [super initWithFrame:rect])) {
        // Get the layer
        CAEAGLLayer *eaglLayer = (CAEAGLLayer *)self.layer;
        
        eaglLayer.opaque = YES;
        eaglLayer.drawableProperties = [NSDictionary dictionaryWithObjectsAndKeys:
                                        [NSNumber numberWithBool:NO], kEAGLDrawablePropertyRetainedBacking, kEAGLColorFormatRGBA8, kEAGLDrawablePropertyColorFormat, nil];
        
        context = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES1];
        
        if (!context || ![EAGLContext setCurrentContext:context]) {
            [self release];
            return nil;
        }
		self.multipleTouchEnabled = YES;
	}
    return self;
}

- (void)layoutSubviews 
{
	[EAGLContext setCurrentContext:context];
	[self destroyFramebuffer];
	[self createFramebuffer];
	[self setupViewLandscape];
}

- (BOOL)createFramebuffer {    
    // 프레임버퍼와, 렌더버퍼를 위한 식별자 값 얻기 (식별자는 GLuint 형 타입)
    glGenFramebuffersOES(1, &viewFramebuffer);
    glGenRenderbuffersOES(1, &viewRenderbuffer);
    
    // 파이프라인에 바인딩 
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
	
    // 렌더버퍼 메모리 할당
    [context renderbufferStorage:GL_RENDERBUFFER_OES fromDrawable:(CAEAGLLayer*)self.layer];
     // 렌더버퍼를 프레임버퍼에 연결 
    glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, viewRenderbuffer);
    
    glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_WIDTH_OES, &backingWidth);
    glGetRenderbufferParameterivOES(GL_RENDERBUFFER_OES, GL_RENDERBUFFER_HEIGHT_OES, &backingHeight);
    
    // 깊이 버퍼도 사용한다면, 위와 동일한 과정으로 생성후 프레임버퍼에 연결
    if (USE_DEPTH_BUFFER) {
        glGenRenderbuffersOES(1, &depthRenderbuffer);
        glBindRenderbufferOES(GL_RENDERBUFFER_OES, depthRenderbuffer);
        glRenderbufferStorageOES(GL_RENDERBUFFER_OES, GL_DEPTH_COMPONENT16_OES, backingWidth, backingHeight);
        glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_DEPTH_ATTACHMENT_OES, GL_RENDERBUFFER_OES, depthRenderbuffer);
    }
    
    if(glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES) != GL_FRAMEBUFFER_COMPLETE_OES) {
        NSLog(@"failed to make complete framebuffer object %x", glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES));
        return NO;
    }
    
    return YES;
}

- (void)destroyFramebuffer {
    
    glDeleteFramebuffersOES(1, &viewFramebuffer);
    viewFramebuffer = 0;
    glDeleteRenderbuffersOES(1, &viewRenderbuffer);
    viewRenderbuffer = 0;
    
    if(depthRenderbuffer) {
        glDeleteRenderbuffersOES(1, &depthRenderbuffer);
        depthRenderbuffer = 0;
    }
}

- (void)setupViewLandscape
{		
	// Sets up matrices and transforms for OpenGL ES
	glViewport(0, 0, backingWidth, backingHeight);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glRotatef(-90.0f, 0.0f, 0.0f, 1.0f);
	// set up the viewport so that it is analagous to the screen pixels
	glOrthof(-backingHeight/2.0, backingHeight/2.0, -backingWidth/2.0, backingWidth/2.0, -1.0f, 1.0f);
	
	glMatrixMode(GL_MODELVIEW);
	
	// Clears the view with black
	glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
}

-(void)perspectiveFovY:(GLfloat)fovY 
                        aspect:(GLfloat)aspect 
			 zNear:(GLfloat)zNear
			   zFar:(GLfloat)zFar 
{
	const GLfloat pi = 3.1415926;
	//	Half of the size of the x and y clipping planes.
	// - halfWidth = left, halfWidth = right
	// - halfHeight = bottom, halfHeight = top
	GLfloat halfWidth, halfHeight;
	//	Calculate the distance from 0 of the y clipping plane. Basically trig to calculate
	//	position of clip plane at zNear.
	halfHeight = tan( (fovY / 2) / 180 * pi ) * zNear;	
	//	Calculate the distance from 0 of the x clipping plane based on the aspect ratio.
	halfWidth = halfHeight * aspect;
	//	Finally call glFrustum with our calculated values.
	glFrustumf( -halfWidth, halfWidth, -halfHeight, halfHeight, zNear, zFar );
}

-(void)beginDraw
{
	// Make sure that you are drawing to the current context
	[EAGLContext setCurrentContext:context];
	glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
	// make sure we are in model matrix mode and clear the frame
	glMatrixMode(GL_MODELVIEW);
	glClear(GL_COLOR_BUFFER_BIT);
	// set a clean transform
	glLoadIdentity();	
}

-(void)finishDraw
{
	glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
	[context presentRenderbuffer:GL_RENDERBUFFER_OES];	
}