xEnOnn

09-01-2011, 08:19 AM

I'm trying to draw a 2D crescent(a moon) but I'm facing a lot of problem. Here's what I've been playing with so far, which have problems with the start and end vertices:

void drawCresent(float step, float radius, float cut) {

float angle=0.0f;

glBegin(GL_POLYGON);

glColor4f(1.0, 1.0, 1.0, 1.0);

glVertex2f(cut*radius*sinf(-1.5f*PI),0);

while (angle<=PI) {

glVertex2f(radius*sinf(angle),radius*cosf(angle));

angle+=step;

}

while (angle<(2.0f*PI)) {

angle+=step;

}

glEnd();

} [/B]

[/B]

Unfortunately, because of the start and end points of the polygon are automatically joined, a straight line is being cut across the polygon and the colour filling of the area is incorrect. The inner curve of the crescent is lost because of the straight line.

I found this method really troublesome and not flexible because I have hardcoded the angles. I was thinking to use the intersection between 2 circles instead. Is it possible to remove an intersection area of a polygon in OpenGL? How can I do it? I've searched the web but have no answers to how I could remove intersected areas between polygons.

If removal of intersections is not possible or turns out to be more complicated, what else can I do to fix the problem in the above code?

Thanks for any help.

void drawCresent(float step, float radius, float cut) {

float angle=0.0f;

glBegin(GL_POLYGON);

glColor4f(1.0, 1.0, 1.0, 1.0);

glVertex2f(cut*radius*sinf(-1.5f*PI),0);

while (angle<=PI) {

glVertex2f(radius*sinf(angle),radius*cosf(angle));

angle+=step;

}

while (angle<(2.0f*PI)) {

angle+=step;

}

glEnd();

} [/B]

[/B]

Unfortunately, because of the start and end points of the polygon are automatically joined, a straight line is being cut across the polygon and the colour filling of the area is incorrect. The inner curve of the crescent is lost because of the straight line.

I found this method really troublesome and not flexible because I have hardcoded the angles. I was thinking to use the intersection between 2 circles instead. Is it possible to remove an intersection area of a polygon in OpenGL? How can I do it? I've searched the web but have no answers to how I could remove intersected areas between polygons.

If removal of intersections is not possible or turns out to be more complicated, what else can I do to fix the problem in the above code?

Thanks for any help.