OpenGL ES显示白色或黑色屏幕

Question

I'm trying to port my desktop OpenGL program to OpenGL ES 1.1 on iOS but I'm having no luck. All the code is the same eg drawArrays and glOrthof, except the framebuffer logic on the iOS side obviously is different, as it takes the place of GLUT which does not exist on iOS. Can someone tell me what is wrong with this code? It tends to show either a white or black screen.

gllayer = (CAEAGLLayer *)self.layer;
gllayer.opaque = TRUE;
gllayer.drawableProperties = @{
    kEAGLDrawablePropertyRetainedBacking: @YES,
    kEAGLDrawablePropertyColorFormat: kEAGLColorFormatRGBA8
};
context = [[EAGLContext alloc] initWithAPI: kEAGLRenderingAPIOpenGLES1];
if (!context || ![EAGLContext setCurrentContext:context]) {
    [self release];
    return nil;
}
glGenFramebuffersOES (1, &framebuffer);
glGenRenderbuffersOES (1, &renderbuffer);
glBindFramebufferOES (GL_FRAMEBUFFER_OES, framebuffer);
glBindRenderbufferOES (GL_RENDERBUFFER_OES, renderbuffer);
[context renderbufferStorage: GL_RENDERBUFFER_OES fromDrawable: gllayer];
glFramebufferRenderbufferOES (GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, renderbuffer);
glGetRenderbufferParameterivOES (GL_RENDERBUFFER_OES, GL_RENDERBUFFER_WIDTH_OES, &backingWidth);
glGetRenderbufferParameterivOES (GL_RENDERBUFFER_OES, GL_RENDERBUFFER_HEIGHT_OES, &backingHeight);
glGenRenderbuffersOES (1, &depthbuffer);
glBindRenderbufferOES (GL_RENDERBUFFER_OES, depthbuffer);
glRenderbufferStorageOES (GL_RENDERBUFFER_OES, GL_DEPTH_COMPONENT16_OES, backingWidth, backingHeight);
glFramebufferRenderbufferOES (GL_FRAMEBUFFER_OES, GL_DEPTH_ATTACHMENT_OES, GL_RENDERBUFFER_OES, depthbuffer);
if (glCheckFramebufferStatusOES (GL_FRAMEBUFFER_OES) != GL_FRAMEBUFFER_COMPLETE_OES)
    return nil;

It looks to me like basically on iOS we're drawing into a buffer. If it were possible to draw directly onto the screen I'd just do that instead.

- (void) startAnimation
{
     displayLink = [NSClassFromString(@"CADisplayLink") displayLinkWithTarget:self
                                                                selector:@selector(drawGLContent)
               ];
     [displayLink setFrameInterval: animationFrameInterval];
     [displayLink addToRunLoop: [NSRunLoop currentRunLoop]
                  forMode:NSDefaultRunLoopMode];

    animating = TRUE;
}

Answer 1

@Frank, I can see that you are having troubles with the OpenGL initialization. Here I've created a MyGLView view that is a UIView that contains all the OpenGL setup code. The EAGLContext, the renderbuffer and the framebuffer are correctly created and destroyed. I have added some comments so you can see what is going on.

Also The method drawGLContent is where you need to place your draw calls specifically under the "TODO" comment.

#import <GLKit/GLKit.h>
#import <Foundation/Foundation.h>

@interface MyGLView : UIView{

    EAGLContext *context;

    GLuint viewRenderbuffer, viewFramebuffer;
}

- (void)drawGLContent;

@end

@implementation MyGLView

// Implement this to override the default layer class (which is [CALayer class]).
// We do this so that our view will be backed by a layer that is capable of OpenGL ES rendering.
+ (Class)layerClass
{
    return [CAEAGLLayer class];
}

- (id)init{
    if ((self = [super init])) {
        [self initView];
    }

    return self;
}

- (id)initWithFrame:(CGRect)frame{
    if ((self = [super initWithFrame:frame])) {
        [self initView];
    }

    return self;
}

- (id)initWithCoder:(NSCoder*)coder {

    if ((self = [super initWithCoder:coder])) {
        [self initView];
    }

    return self;
}

- (void)initView{
    CAEAGLLayer *eaglLayer = (CAEAGLLayer *)self.layer;

    eaglLayer.opaque = YES;
    // In this application, we want to retain the EAGLDrawable contents after a call to presentRenderbuffer.
    eaglLayer.drawableProperties = [NSDictionary dictionaryWithObjectsAndKeys:
                                    [NSNumber numberWithBool:YES], kEAGLDrawablePropertyRetainedBacking, kEAGLColorFormatRGBA8, kEAGLDrawablePropertyColorFormat, nil];

    context = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES1];

    if (!context || ![EAGLContext setCurrentContext:context]) {
        NSLog(@"failed to init HeatmapView");
    }

    // Set the view's scale factor as you wish
    self.contentScaleFactor = [[UIScreen mainScreen] scale];

    [EAGLContext setCurrentContext:context];

    [self createBuffers];
}

- (void)createBuffers{

    // The pixel dimensions
    GLint backingWidth;
    GLint backingHeight;

    // Generate IDs for a framebuffer object and a color renderbuffer
    glGenFramebuffers(1, &viewFramebuffer);
    glGenRenderbuffers(1, &viewRenderbuffer);

    glBindFramebuffer(GL_FRAMEBUFFER, viewFramebuffer);
    glBindRenderbuffer(GL_RENDERBUFFER, viewRenderbuffer);
    // This call associates the storage for the current render buffer with the EAGLDrawable (our CAEAGLLayer)
    // allowing us to draw into a buffer that will later be rendered to screen wherever the layer is (which corresponds with our view).
    [context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(id<EAGLDrawable>)self.layer];
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, viewRenderbuffer);

    glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &backingWidth);
    glGetRenderbufferParameteriv(GL_RENDERBUFFER,   GL_RENDERBUFFER_HEIGHT, &backingHeight);

    if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
    {
        NSLog(@"failed to make complete framebuffer object %x", glCheckFramebufferStatus(GL_FRAMEBUFFER));
    }

    // Setup the view port in Pixels
    glViewport(0, 0, backingWidth ,backingHeight);
}

- (void)destroyBuffers{

    // Destroy framebuffers and renderbuffers
    if (viewFramebuffer) {
        glDeleteFramebuffers(1, &viewFramebuffer);
        viewFramebuffer = 0;
    }
    if (viewRenderbuffer) {
        glDeleteRenderbuffers(1, &viewRenderbuffer);
        viewRenderbuffer = 0;
    }
}

#pragma mark - Public methods

- (void)drawGLContent{

    [EAGLContext setCurrentContext:context];

    if(viewRenderbuffer == 0 || viewFramebuffer == 0){
        [self createBuffers];
    }

    //Clear the framebuffer
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glClear(GL_COLOR_BUFFER_BIT);

    ///////////////////////////////////////////
    //TODO:MAKE Draw Calls!!
    ///////////////////////////////////////////

    // Display the buffer
    [context presentRenderbuffer:GL_RENDERBUFFER];
}

#pragma mark -

- (BOOL)pointInside:(CGPoint)point withEvent:(UIEvent *)event {
    return NO;
}

-(void)layoutSubviews
{
    [EAGLContext setCurrentContext:context];

    [self destroyBuffers];
    [self createBuffers];

    //Clear the framebuffer
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glClear(GL_COLOR_BUFFER_BIT);
    [context presentRenderbuffer:GL_RENDERBUFFER];
}

- (void)dealloc
{
    [self destroyBuffers];

    // tear down context
    if ([EAGLContext currentContext] == context)
        [EAGLContext setCurrentContext:nil];
}

@end

This class is based in Ray Wenderlich OpenGL ES 2.0 tutorials but slightly adapted to OpenGL ES 1.0.