为什么调用glMatrixMode（GL_PROJECTION）在iPhone应用程序中给我EXC_BAD_ACCESS？ [英] Why does calling glMatrixMode(GL_PROJECTION) give me EXC_BAD_ACCESS in an iPhone app?

问题描述

我有一个iphone应用程序，我在appDidFinishLaunching中调用这三个函数：

I have an iphone app where I call these three functions in appDidFinishLaunching:

glMatrixMode(GL_PROJECTION);
glOrthof(0, rect.size.width, 0, rect.size.height, -1, 1);
glMatrixMode(GL_MODELVIEW);

当我使用调试器时，我执行第一行时得到EXC BAD ACCESS。任何想法为什么会发生这种情况？

When stepping through with the debugger I get EXC BAD ACCESS when I execute the first line. Any ideas why this is happening?

顺便说一下，我有另一个应用程序，我做同样的事情，它工作正常。所以我试图复制该应用程序中的所有内容（#imports，添加OpenGLES框架等），但现在我只是卡住了。

Btw I have another application where I do the same thing and it works fine. So I've tried to duplicate everything in that app (#imports, adding OpenGLES framework, etc) but now I'm just stuck.

推荐答案

如果两个线程试图立即绘制到OpenGL场景，我会遇到OpenGL调用。但是，这听起来不像你正在做的那样。

I've run into this with OpenGL calls if two threads are attempting to draw to the OpenGL scene at once. However, that doesn't sound like what you're doing.

你是否在此次通话之前正确初始化了显示上下文和帧缓冲？例如，在我执行OpenGL绘图的UIView子类中，我在其initWithCoder中调用以下内容：方法：

Have you properly initialized your display context and framebuffer before this call? For example, in my UIView subclass that does OpenGL drawing, I call the following in its initWithCoder: method:

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

if (!context || ![EAGLContext setCurrentContext:context] || ![self createFramebuffer]) 
{
    [self release];
    return nil;
}

createFramebuffer方法如下所示：

The createFramebuffer method looks like the following:

- (BOOL)createFramebuffer 
{   
    glGenFramebuffersOES(1, &viewFramebuffer);
    glGenRenderbuffersOES(1, &viewRenderbuffer);

    glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
    [context renderbufferStorage:GL_RENDERBUFFER_OES fromDrawable:(CAEAGLLayer*)self.layer];
    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);

    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) 
    {
        return NO;
    }

    return YES;
}

这是一个样板代码，由OpenGL ES Application模板生成XCode中。也许在调用glMatrixMode（）之前没有初始化东西，你就会崩溃。

This is pretty much boilerplate code, as generated by the OpenGL ES Application template in XCode. Perhaps by not initializing things before calling glMatrixMode(), you're getting a crash.

另外，你为什么要在applicationDidFinishLaunching中进行OpenGL绘图？对于OpenGL调用，视图或视图控制器不是比UIApplicationDelegate更适合的地方吗？

Also, why are you doing OpenGL drawing in applicationDidFinishLaunching:? Wouldn't a view or view controller be a more appropriate place for OpenGL calls than your UIApplicationDelegate?

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