Issue with glPolygonMode - GL_FILL "skipping" vertices

Question

I'm having a weird issue when trying to draw a polygon and filling it with a particular color:

If I set the polygon mode as:

glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

The polygon renders just fine:

However, as soon as I replace that line with the following:

glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);

The polygon doesn't fill right, but it seems like most lines get projected towards its first vertex, or something along those lines:

I'm obviously doing something wrong. What I want to do is keep the color inside the polygon, however it seems to be ignoring several vertices. What might be wrong?

Here's some selected parts of my code that might be of interest. I'm skipping over some data structures loading and other stuff that might not be very relevant:

int main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE);

    glutInitWindowSize(640, 480);
    glutInitWindowPosition(150, 100);
    glutCreateWindow("CR-View GL");

    glutDisplayFunc(display);

    glutMainLoop();
    return 0;
}

void display(void) {
    glClearColor(0, 0, 0, 0);
    glClear(GL_COLOR_BUFFER_BIT);
    /* Set drawing color */
    glColor3f(1, 0, 1);

    drawPolys(currentDrawingMode);

    /* Clear screen and draw */
    glutSwapBuffers();
}

// Draws the polygons
void drawPolys (int id) {   
    int poly, vertex;
    // set wireframe mode (if an empty polygon is required)
    if (id == 0) {
        glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
    }

    //Sets color fill mode
    if (id == 1) {
        glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
    }

    // Draw each polygon...
    for (poly = 0; poly < polyCount; poly++) {

        glBegin(GL_POLYGON);
            // Draw each vertex...
        for (vertex = 0; vertex < Polygons[poly].vertexCount; vertex++) {
            glVertex2f((float)Polygons[poly].vertices[vertex].x, (float)Polygons[poly].vertices[vertex].y);
        }
        glEnd();
    } 
}

Answer 1

If you're using GL_POLYGON be aware that it only supports convex polygons.