CODEWITHSUNDEEP
c++opengldrawinggeometryorthographic
Ana
Ana

Reputation: 19

Drawing circle on OpenGL

This code is supposed to just draw a circle on a window, but the circle doesn't show up. I'm using the function glVertex2f.

#include <GLUT/glut.h>
#include <math.h>

void init(void) {
    glClearColor(0.686, 0.933, 0.933,0.0);
    glMatrixMode(GL_PROJECTION);
    gluOrtho2D(0.0,200.0,0.0,150.0);
}
void lineSegment(void) {
    float theta;
    int posX = 400;
    int posY = 400;
    int radio = 100;
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(0.0,0.4,0.2);
    glBegin(GL_POLYGON);
    for(int i=0; i<360; i++){
        theta = i*3.1416/180;
        glVertex2f(posX + radio*cos(theta), posY + radio*sin(theta));
    }
    glEnd();
    glFlush();
}


int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowPosition(50,50);
    glutInitWindowSize(800,800);
    glutCreateWindow("Cerámica Ana");
    init();
    glutDisplayFunc(lineSegment);
    glutMainLoop();
}

Upvotes: 1

Views: 6986

Answers (1)

Rabbid76
Rabbid76

Reputation: 211229

You have setup an orthographic projection:

gluOrtho2D(0.0,200.0,0.0,150.0);

The geometry within the rectangle, which is defined by the orthographic projection, is projected on the viewport. This means, that the geometry with coordinates form (0,0) to (200, 150) is visible on the viewport. The geometry out of this area is clipped.

But the center of the circle is at (500, 500) and is radius is 100. So it is not inside the clipping region.

Since the size of the viewport is (800, 800), I reommeend to adapt the orthgraphic projection to the viewport.
See gluOrtho2D and glOrtho.

Change the orthographic projection to solve the issue:

glMatrixMode(GL_PROJECTION);
gluOrtho2D(0.0, 800.0, 0.0, 800.0);

Upvotes: 3

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