Hello from Germany :)
I created 2 triangles with different vertex order (counter clockwise and
clockwise). This orders are user data and may not be changed.
For the flat shading the view is ok. But for the smooth shading I
get partial or full black triangles for the clockwise orders :(
The problem is that I have only 1 averaged normal for a vertex.
Is there a openGl statement to correct this mistake?
Are the normals to be set principle after the "right hand rule"?
Thanks in advance
Greetings
hoon
Here's is a pic:
import javax.swing.*;
import javax.media.opengl.GLEventListener;
import javax.media.opengl.GLCanvas;
import javax.media.opengl.GLAutoDrawable;
import javax.media.opengl.GL;
import javax.media.opengl.glu.GLU;
import java.nio.FloatBuffer;
public class NormalProblem
extends JFrame
implements GLEventListener
{
private static final boolean SMOOTH = true;
private int angle = 0;
public static void main(final String[] args)
{
new NormalProblem();
}
public NormalProblem()
{
final GLCanvas canvas = new GLCanvas();
canvas.addGLEventListener(this);
add(canvas);
setSize(500, 500);
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
while (isWoken())
canvas.display();
}
public void display(final GLAutoDrawable drawable)
{
final GL gl = drawable.getGL();
gl.glClear(GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT);
gl.glLoadIdentity();
gl.glTranslatef(0, 0, -6);
gl.glRotated(angle, 1, 1, 1);
gl.glRotated(angle++, 0, 1, 0);
/* 3
* / * / 1 \ triangle 1 [1, 2, 3] (counter clockwise vertex order)
* 1/_____\ 2
* \ /
* y \ 2 / triangle 2 [1, 2, 4] (clockwise vertex order)
* ^ \ /
* | 4
* '---> x
*/
if (SMOOTH)
gl.glShadeModel(GL.GL_SMOOTH);
else
gl.glShadeModel(GL.GL_FLAT);
drawTriangles(gl);
drawNormals(gl);
}
private void drawTriangles(final GL gl)
{
gl.glBegin(GL.GL_TRIANGLES);
if (SMOOTH)
{
// triangle 1 [1, 2, 3]
gl.glNormal3f(0, 0, 1);
gl.glVertex3f(-2, 0, 0);
gl.glNormal3f(0, 0, 1);
gl.glVertex3f(2, 0, 0);
gl.glNormal3f(0, 0, 1);
gl.glVertex3f(0, 2, 0);
// triangle 2 [1, 2, 4]
gl.glNormal3f(0, 0, 1); // (0, 0, -1) is correct but I have only "one" vertex normal
gl.glVertex3f(-2, 0, 0);
gl.glNormal3f(0, 0, 1); // (0, 0, -1) is correct but I have only "one" vertex normal
gl.glVertex3f(2, 0, 0);
gl.glNormal3f(0, 0, -1);
gl.glVertex3f(0, -2, 0);
}
else
{
// triangle 1 [1, 2, 3]
gl.glNormal3f(0, 0, 1);
gl.glVertex3f(-2, 0, 0);
gl.glVertex3f(2, 0, 0);
gl.glVertex3f(0, 2, 0);
// triangle 2 [1, 2, 4]
gl.glNormal3f(0, 0, -1);
gl.glVertex3f(-2, 0, 0);
gl.glVertex3f(2, 0, 0);
gl.glVertex3f(0, -2, 0);
}
gl.glEnd();
}
private void drawNormals(final GL gl)
{
gl.glDisable(GL.GL_LIGHTING);
gl.glBegin(GL.GL_LINES);
if (SMOOTH)
{
gl.glColor3f(1, 1, 0);
// vertex normals of triangle 1 [1, 2, 3]
// common normal on vertex 1 for triangle 1 and 2
gl.glVertex3f(-2, 0, 0);
gl.glVertex3f(-2, 0, 1);
// common normal on vertex 2 for triangle 1 and 2
gl.glVertex3f(2, 0, 0);
gl.glVertex3f(2, 0, 1);
gl.glColor3f(0, 1, 0);
gl.glVertex3f(0, 2, 0);
gl.glVertex3f(0, 2, 1);
gl.glColor3f(1, 0, 0);
// vertex normals of triangle 2 [1, 2, 4]
/* normals for vertex 1 and 2 already exist
gl.glVertex3f(-2, 0, 0);
gl.glVertex3f(-2, 0, -1);
gl.glVertex3f(2, 0, 0);
gl.glVertex3f(2, 0, -1);
*/
gl.glVertex3f(0, -2, 0);
gl.glVertex3f(0, -2, -1);
}
else
{
gl.glColor3f(0, 1, 0);
// normal of triangle 1 [1, 2, 3]
gl.glVertex3f(0, 1, 0);
gl.glVertex3f(0, 1, 1);
gl.glColor3f(1, 0, 0);
// normal of triangle 2 [1, 2, 4]
gl.glVertex3f(0, -1, 0);
gl.glVertex3f(0, -1, -1);
}
gl.glEnd();
gl.glEnable(GL.GL_LIGHTING);
}
public void init(final GLAutoDrawable drawable)
{
final GL gl = drawable.getGL();
gl.glEnable(GL.GL_DEPTH_TEST);
gl.glLightModeli(GL.GL_LIGHT_MODEL_TWO_SIDE, GL.GL_TRUE);
gl.glEnable(GL.GL_LIGHT0);
gl.glEnable(GL.GL_LIGHTING);
gl.glLightfv(GL.GL_LIGHT0, GL.GL_AMBIENT, FloatBuffer.wrap(new float[]{0, 0, 0, 1}));
gl.glLightfv(GL.GL_LIGHT0, GL.GL_DIFFUSE, FloatBuffer.wrap(new float[]{1, 1, 1, 1}));
gl.glLightfv(GL.GL_LIGHT0, GL.GL_SPECULAR, FloatBuffer.wrap(new float[]{1, 1, 1, 1}));
gl.glLightfv(GL.GL_LIGHT0, GL.GL_POSITION, FloatBuffer.wrap(new float[]{0, 0, 6}));
gl.glMaterialfv(GL.GL_FRONT_AND_BACK, GL.GL_AMBIENT, FloatBuffer.wrap(new float[]{0.2f, 0.1f, 0, 1}));
gl.glMaterialfv(GL.GL_FRONT_AND_BACK, GL.GL_DIFFUSE, FloatBuffer.wrap(new float[]{0.6f, 0.2f, 0.1f, 1}));
gl.glMaterialfv(GL.GL_FRONT_AND_BACK, GL.GL_SPECULAR, FloatBuffer.wrap(new float[]{0.6f, 0.2f, 0.1f, 1}));
gl.glMaterialfv(GL.GL_FRONT_AND_BACK, GL.GL_EMISSION, FloatBuffer.wrap(new float[]{0, 0, 0, 1}));
gl.glMaterialf(GL.GL_FRONT_AND_BACK, GL.GL_SHININESS, 50);
gl.glMatrixMode(GL.GL_PROJECTION);
gl.glLoadIdentity();
new GLU().gluPerspective(50, drawable.getWidth() / drawable.getHeight(), 1, 1000);
gl.glMatrixMode(GL.GL_MODELVIEW);
gl.glLoadIdentity();
gl.glLineWidth(3);
}
private boolean isWoken()
{
try
{
Thread.sleep(10);
}
catch (InterruptedException e)
{
e.printStackTrace();
}
return true;
}
public void reshape(
final GLAutoDrawable drawable,
final int x,
final int y,
final int width,
final int height)
{
}
public void displayChanged(
final GLAutoDrawable drawable,
final boolean mode,
final boolean device)
{
}
}
And here's is the code with jogl (executable):
