need help

OpenGL
1

Hay,guys! I would appreciate any of you if can give me some comments about the following question.

I write a class for circles as following;
class glCircle
{
public:
glCircle(GLint x=0,GLint y=0,GLint r=50);
void setColor(GLfloat r=1.0,GLfloat g=0, GLfloat b=0);
void plot(void);

private:
GLint xCenter;
GLint yCenter;
GLint radius;
void setPixel(GLint xCoord,GLint yCoord);
void midpoint();
void plotPoints(screenPt circPt);
};

and plot function like this,

void glCircle::plot(void)
{
//Clear display window
glClear(GL_COLOR_BUFFER_BIT);

//activate the antialias
glEnable(GL_POINT_SMOOTH);

//declare the identifiers
GLuint regCircle;

//get an identifier for the circle routine
regCircle=glGenLists(1);
glNewList(regCircle,GL_COMPILE);
	midpoint();
glEndList();

//Call lists here
glCallList(regCircle);

//Process all OpenGl routines as quickly as possible
glFlush();

}

Now I want to call this plot in main function as follow,
glCircle circle;
glutDisplayFunc(circle.plot);

when I compile using VC++, the following error occurs,

glutDisplayFunc’ : cannot convert parameter 1 from ‘void (void)’ to ‘void (__cdecl *)(void)’
None of the functions with this name in scope match the target type.

Did any of you have the situation before?

Thanks in anticipation.

2

the problem seems to be that you want to use a class member function. to avoid this, try:

glCircle   circle;

void plot_circle() {
 circle.plot();}

...

main() {

...

glutDisplayFunc(plot_circle);
}

by the way, usually you don’t clear the color buffer in a class member function. if you have two circles and plot them both the buffer will be cleared twice. a better way would look like

glCircle  circles[3];

void plot_circles(){

 glClear();

 for(int i = 0; i < 3; i ++)
   circles[i].plot();

 glFlush();}

about display lists: it doesn’t make so much sense to call a display list right after you’ve created it. usually you create a list ONCE at program start (assuming that your model geometry does not change) and then call it in the plot() function.

3

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