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  Drawing a Circle  (Read 2193 times)
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Offline ajaskey

Junior Newbie





« Posted 2006-11-09 22:41:43 »

Hi.  I'm slowly figuring how to draw various "stuff" I need in my application.  This scratchpad app is used to test stuff.  Everything in the following code works but I cannot figure out how to draw a circle.  I'd appreciate some help.  I've tried the following calls with no luck.  Either I am using the wrong calls to draw an unfilled circle or I am missing additional calls to make them work. 

glu.gluSphere
glut.glutWireSphere
glut.glutSolidSphere

I want to draw the circle near the middle of the virtual coordinates (around 7500,7500).  Here is what I have that does work.

Thanx.  Andy

-----------------

    public void init(GLAutoDrawable drawable) {
        // Use debug pipeline
        // drawable.setGL(new DebugGL(drawable.getGL()));
        GL gl = drawable.getGL();
        System.err.println("INIT GL IS: " + gl.getClass().getName());       
        gl.glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
        gl.glShadeModel(GL.GL_FLAT);
     }

    public void reshape(GLAutoDrawable drawable, int x, int y, int width, int height) {
        GL gl = drawable.getGL();
        gl.glViewport(0, 0, width, height);
        gl.glMatrixMode(GL.GL_PROJECTION);
        gl.glLoadIdentity();
        gl.glOrtho(-1000,15000,-1000,15000,-1,1);
    }
   
    public void display(GLAutoDrawable drawable) {
        GL gl = drawable.getGL();
        GLU glu = new GLU();
        GLUT glut = new GLUT();       
        int font18 = GLUT.BITMAP_HELVETICA_18;
        int font10 = GLUT.BITMAP_HELVETICA_10;
        int font_a = GLUT.BITMAP_8_BY_13;
               
        // Draw Rectange
        gl.glClear(GL.GL_COLOR_BUFFER_BIT);
        gl.glColor3f(1, 0, 0);
        gl.glRecti(100, 100, 1500, 1500);
       
        // Draw Line
        gl.glBegin(GL.GL_LINES);
        gl.glVertex2i(7500,7500);
        gl.glVertex2i(14000,14000);
        gl.glEnd();
       
        // Draw Text
        gl.glColor3f(0.0f, 1.0f, 0.0f);
        gl.glRasterPos3f(1000.0f,1000.0f,0.0f);
        glut.glutBitmapString(font18, "TEST18");
       
        gl.glRasterPos3f(6000.0f,8000.0f,0.0f);
        glut.glutBitmapString(font10, "TEST10");
       
        gl.glRasterPos3f(8000.0f,12000.0f,0.0f);
        glut.glutBitmapString(font_a, "TEST_A");
       
        gl.glColor3f(0.0f, 0.0f, 0.0f);
     }
   
    public void displayChanged(GLAutoDrawable drawable, boolean modeChanged, boolean deviceChanged) {
    }
Offline turquoise3232

Junior Member




Java (games) rock!


« Reply #1 - Posted 2006-11-10 08:49:36 »

Hi,

To draw a 2D circle you need to approximate it by a succession of small lines ( for loop with some sin and cos calls).
So a very little math and you'll have a circle.
Offline eteq

Junior Member





« Reply #2 - Posted 2006-11-13 18:35:59 »

And if your not up for the working out the math, this should work:
1  
2  
3  
4  
gl.glBegin(gl.GL_LINES);
for (int t = 0; t < 2 Pi; t+= stepsize)
   gl.glVertex2d(Math.sin(t),Math.cost));
gl.glEnd();

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