C++ 在类中使用 OpenGL glutDisplayFunc
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Using OpenGL glutDisplayFunc within class
提问by Nicholas Kinar
I've created a C++ class (myPixmap) to encapsulate the work performed by the OpenGL GLUT toolkit. The display()member function of the class contains most of the code required to set up GLUT.
我创建了一个 C++ 类 ( myPixmap) 来封装由 OpenGL GLUT 工具包执行的工作。display()该类的成员函数包含设置 GLUT 所需的大部分代码。
void myPixmap::display()
{
// open an OpenGL window if it hasn't already been opened
if (!openedWindow)
{
// command-line arguments to appease glut
char *argv[] = {"myPixmap"};
int argc = 1;
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize(640, 480);
glutInitWindowPosition(30, 30);
glutCreateWindow("Experiment");
glutDisplayFunc(draw);
glClearColor(0.9f, 0.9f, 0.9f, 0.0);
glClear(GL_COLOR_BUFFER_BIT);
glutMainLoop();
openedWindow = true;
}
}
The display function passed to glutDisplayFunc()is another member function of the class:
传递给的显示函数glutDisplayFunc()是该类的另一个成员函数：
void myPixmap::draw(void)
{
glDrawPixels( m,n,GL_RGB,GL_UNSIGNED_BYTE, pixel );
}
However, gcc 4.2.1 on Mac OS X 10.6.4 refuses to compile this code, claiming that:
但是，Mac OS X 10.6.4 上的 gcc 4.2.1 拒绝编译此代码，声称：
argument of type 'void (myPixmap::)()' does not match 'void (*)()'
argument of type 'void (myPixmap::)()' does not match 'void (*)()'
Is there a way to use the GLUT toolkit inside a member function of a class, or must I call all GLUT functions within the mainfunction of the program?
有没有办法在类的成员函数中使用 GLUT 工具包，或者我必须main在程序的函数中调用所有的 GLUT 函数？
回答by Merlyn Morgan-Graham
The problem is that a pointer to an instance bound member function has to include the thispointer. OpenGL is a C API, and knows nothing about thispointers. You'll have to use a static member function (which doesn't require an instance, and thus no this), and set some static data members (to access the instance) in order to use glutDisplayFunc.
问题是指向实例绑定成员函数的this指针必须包含该指针。OpenGL 是一个 C API，对this指针一无所知。您必须使用静态成员函数（它不需要实例，因此不需要this），并设置一些静态数据成员（以访问实例）才能使用glutDisplayFunc.
class myPixmap
{
private:
static myPixmap* currentInstance;
static void drawCallback()
{
currentInstance->draw();
}
void setupDrawCallback()
{
currentInstance = this;
::glutDisplayFunc(myPixmap::drawCallback);
}
};
You may also have problems with C linkage vs C++ linkage, in which case you'll have to play around with extern "C". If so, you might have to use a global function, rather than a static member function as your callback, and have thatcall myPixmap::draw. Something like:
您可能还会遇到 C 链接与 C++ 链接的问题，在这种情况下，您必须使用extern "C". 如果是这样，您可能必须使用全局函数，而不是静态成员函数作为回调，并使用该调用myPixmap::draw. 就像是：
class myPixmap
{
public:
void draw();
private:
void setupDrawCallback();
};
myPixmap* g_CurrentInstance;
extern "C"
void drawCallback()
{
g_CurrentInstance->draw();
}
void myPixmap::setupDrawCallback();
{
::g_CurrentInstance = this;
::glutDisplayFunc(::drawCallback);
}
With all of this, try to make as few changes as possible, since this is really kind of a kludge to deal w/ OpenGL being a C API.
有了所有这些，尽量少做一些改变，因为这真的是一种处理 OpenGL 作为 C API 的麻烦。
If you want multiple instances (I don't think most people using GLUT make multiple instances, but maybe you are), you'll have to figure out a solution using a std::map to retrieve the instance:
如果您想要多个实例（我认为大多数使用 GLUT 的人不会创建多个实例，但也许您是），您必须找出使用 std::map 检索实例的解决方案：
static std::map<int, myPixmap> instanceMap;
Where you'd get the intto resolve whichinstance, I am not sure :)
你在哪里可以int解决哪个实例，我不确定:)
FYI, you should define functions that take no parameters this way:
仅供参考，您应该以这种方式定义不带参数的函数：
void some_function() { }
not
不是
void some_function(void) { }
回答by shox_de_coder
Please check this tutorial, I think this is what you are looking for: http://paulsolt.com/2010/08/glut-object-oriented-framework-on-github/
请查看本教程，我认为这就是您要查找的内容：http: //paulsolt.com/2010/08/glut-object-oriented-framework-on-github/
回答by Tqq
Merlyn solution didnt work for me, so I made a little modification by bringing currentInstance outside of class and it worked:
Merlyn 解决方案对我不起作用，所以我通过将 currentInstance 带到课堂之外进行了一些修改，它起作用了：
Class myPixmap;
static myPixmap* currentInstance;
Class myPixmap {
...
}
回答by Volodymyr Balytskyy
I had trouble in understanding the correct answer from Merlyn, so here it is the simplified version:
我无法理解 Merlyn 的正确答案，所以这里是简化版：
In myPixmap.h, change display function to staticmember function. Should work.
在myPixmap.h 中，将显示函数更改为静态成员函数。应该管用。
class myPixmap
{
//...
static void display();
//...
};
