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In the Previous chapters we have learned how draw a shapes such as line, triangle, rhombus using JOGL. We draw lines by passing a predefined field, Gl_lines to glBegin() method.
Other than GL_LINES, the glBegin() method accepts eight more parameters. You can use them to draw different shapes. These are used the same way as GL_LINES.
The following table shows the glBegin() method parameters along with their description −
| Sr.No | Parameters and Description |
|---|---|
| 1 |
GL_LINES Creates each pair of vertices as an independent line segment. |
| 2 |
GL_LINE_STRIP Draws a connected group of line segments from the first vertex to the last. |
| 3 |
GL_LINE_LOOP Draws a connected group of line segments from the first vertex to the last, again back to the first. |
| 4 |
GL_TRIANGLES Treats each triplet of vertices as an independent triangle. |
| 5 |
GL_TRIANGLE_STRIP Draws a connected group of triangles. One triangle is defined for each vertex presented after the first two vertices. |
| 6 |
GL_TRIANGLE_FAN Draws a connected group of triangles. One triangle is defined for each vertex presented after the first two vertices. |
| 7 |
GL_QUADS Treats each group of four vertices as an independent quadrilateral. |
| 8 |
GL_QUAD_STRIP Draws a connected group of quadrilaterals. One quadrilateral is defined for each pair of vertices presented after the first pair. |
| 9 |
GL_POLYGON Draws a single, convex polygon. Vertices 1,…,n define this polygon. |
Let us see some examples using glBegin() parameters.
Program to draw a Line Strip
import javax.media.opengl.GL2;
import javax.media.opengl.GLAutoDrawable;
import javax.media.opengl.GLCapabilities;
import javax.media.opengl.GLEventListener;
import javax.media.opengl.GLProfile;
import javax.media.opengl.awt.GLCanvas;
import javax.swing.JFrame;
public class LineStrip implements GLEventListener {
@Override
public void display(GLAutoDrawable drawable) {
final GL2 gl = drawable.getGL().getGL2();
gl.glBegin (GL2.GL_LINE_STRIP);
gl.glVertex3f(-0.50f,-0.75f, 0);
gl.glVertex3f(0.7f,0.5f, 0);
gl.glVertex3f(0.70f,-0.70f, 0);
gl.glVertex3f(0f,0.5f, 0);
gl.glEnd();
}
@Override
public void dispose(GLAutoDrawable arg0) {
//method body
}
@Override
public void init(GLAutoDrawable arg0) {
// method body
}
@Override
public void reshape(GLAutoDrawable arg0, int arg1, int arg2, int arg3, int arg4) {
// method body
}
public static void main(String[] args) {
//getting the capabilities object of GL2 profile
final GLProfile profile = GLProfile.get(GLProfile.GL2);
GLCapabilities capabilities = new GLCapabilities(profile);
// The canvas
final GLCanvas glcanvas = new GLCanvas(capabilities);
LineStrip r = new LineStrip();
glcanvas.addGLEventListener(r);
glcanvas.setSize(400, 400);
//creating frame
final JFrame frame = new JFrame ("LineStrip");
//adding canvas to frame
frame.getContentPane().add(glcanvas);
frame.setSize(frame.getContentPane().getPreferredSize());
frame.setVisible(true);
}//end of main
}//end of classimport javax.media.opengl.GL2;
If you compile and execute the above code, the following output is generated −
Code snippet for display() method to draw a Line Loop
public void display(GLAutoDrawable drawable) {
final GL2 gl = drawable.getGL().getGL2();
gl.glBegin (GL2.GL_LINE_LOOP);
gl.glVertex3f( -0.50f, -0.75f, 0);
gl.glVertex3f(0.7f, .5f, 0);
gl.glVertex3f(0.70f, -0.70f, 0);
gl.glVertex3f(0f, 0.5f, 0);
gl.glEnd();
}
If you replace the display() method of any of the basic template programs with the above code, compile, and execute it, the following output is generated −
Code snippet for display() method to draw a triangle using GL_TRIANGLES
public void display(GLAutoDrawable drawable) {
final GL2 gl = drawable.getGL().getGL2();
gl.glBegin(GL2.GL_TRIANGLES); // Drawing Using Triangles
gl.glVertex3f(0.5f,0.7f,0.0f); // Top
gl.glVertex3f(-0.2f,-0.50f,0.0f); // Bottom Left
gl.glVertex3f(0.5f,-0.5f,0.0f); // Bottom Right
gl.glEnd();
}
If you replace the display() method of any of the basic template programs with the above code, compile, and execute it, the following output is generated −
Code snippet for display() method to draw a Triangle Strip
public void display(GLAutoDrawable drawable) {
final GL2 gl = drawable.getGL().getGL2();
gl.glBegin (GL2.GL_TRIANGLE_STRIP);
gl.glVertex3f(0f,0.5f,0);
gl.glVertex3f(-0.50f,-0.75f,0);
gl.glVertex3f(0.28f,0.06f,0);
gl.glVertex3f(0.7f,0.5f,0);
gl.glVertex3f(0.7f,-0.7f,0);
gl.glEnd();
}
If you replace the display() method of any of the basic template programs with the above code, compile and execute it, the following output is generated −
Code snippet for display() method to draw a quadrilateral
public void display(GLAutoDrawable drawable) {
final GL2 gl = drawable.getGL().getGL2();
gl.glBegin(GL2.GL_QUADS);
gl.glVertex3f( 0.0f,0.75f,0);
gl.glVertex3f(-0.75f,0f,0);
gl.glVertex3f(0f,-0.75f,0);
gl.glVertex3f(0.75f,0f,0);
gl.glEnd();
}
If you replace the display() method of any of the basic template programs with the above code, compile, and execute it, the following output is generated −
Code snippet for display() method to draw a polygon
public void display(GLAutoDrawable drawable) {
final GL2 gl = drawable.getGL().getGL2();
gl.glBegin(GL2.GL_POLYGON);
gl.glVertex3f(0f,0.5f,0f);
gl.glVertex3f(-0.5f,0.2f,0f);
gl.glVertex3f(-0.5f,-0.2f,0f);
gl.glVertex3f(0f,-0.5f,0f);
gl.glVertex3f(0f,0.5f,0f);
gl.glVertex3f(0.5f,0.2f,0f);
gl.glVertex3f(0.5f,-0.2f,0f);
gl.glVertex3f(0f,-0.5f,0f);
gl.glEnd();
}
If you replace display() method of any of the basic template programs with the above code, compile, and execute it, the following output is generated −
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