macOS OpenGL in draw rect

[Duke Leto]

I have a circle drawn in an NSOpenGL view, but the OpenGL units and the frame units are very different.

Given a square size, how can I make a circle to fit the frame? It seems like a guessing game!

I am very new to OpenGL, as I started to figure some things out just yesterday, so go easy on me please

Almost forgot, here's the code:

void glCircle3i3d(GLint x, GLint y, GLint rad, GLdouble red, GLdouble green, GLdouble blue) { 
    float angle; 
    glPushMatrix(); 
    glLoadIdentity(); 
    glDisable(GL_TEXTURE_2D); 
    glLineWidth(1.0f); 
    glBegin(GL_POLYGON); 
    glColor3d(red, green, blue);
    for(int i = 0; i < 100; i++) { 
        angle = i*2*M_PI/100; 
        glVertex2f(x + (cos(angle) * rad), y + (sin(angle) * rad)); 
    } 
    glEnd(); 
    glEnable(GL_TEXTURE_2D); 
    glPopMatrix(); 
}  

- (void)drawRect:(NSRect)rect
{
	glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
	glLoadIdentity();   // Reset the current modelview matrix
	glCircle3i3d(0, 0, rect.size.width/2, myColor.red, myColor.green,
myColor.blue);
	[[self openGLContext] flushBuffer];
}

 

[autorelease]

Are you using orthographic or perspective projection?

If you're using perspective projection, you won't be able to make a circle fit the frame without some very serious math.

If this is a 2D application, you should use orthographic projection, because you can make pixel coordinates correspond easily to world coordinates. If you set up your projection matrix with

gluOrtho2D(0.0, viewWidth, 0.0, viewHeight);

then world coordinates will be identical to pixel coordinates.

OpenGL is not easy. It can take skilled programmers months or even years to master it.