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3D 基础知识（3D Basics）

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2023-12-01

在前面的章节中，我们已经了解了如何创建2D对象，对其应用效果以及转换对象。 本章将教您如何绘制具有第三维和某些形状的线。

让我们用z轴画一条简单的线，看看2D和3D线之间的区别。 首先绘制一条简单的线，然后将第二条线3个单位绘制到窗口中。

让我们通过该程序绘制3D线 -

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.media.opengl.glu.GLU;
import javax.swing.JFrame;
public class Line3d implements GLEventListener {
   private GLU glu = new GLU();
   @Override
   public void display( GLAutoDrawable drawable ) {
      final GL2 gl = drawable.getGL().getGL2();
      gl.glTranslatef( 0f, 0f, -2.5f );
      gl.glBegin( GL2.GL_LINES );
      gl.glVertex3f( -0.75f,0f,0 );
      gl.glVertex3f( 0f,-0.75f, 0 );
      gl.glEnd();
      //3d line
      gl.glBegin( GL2.GL_LINES );
      gl.glVertex3f( -0.75f,0f,3f );// 3 units into the window
      gl.glVertex3f( 0f,-0.75f,3f );
      gl.glEnd();
   }
   @Override
   public void dispose( GLAutoDrawable arg0 ) {
      //method body
   }
   @Override
   public void init( GLAutoDrawable arg0 ) {
      // method body
   }
   @Override
   public void reshape( GLAutoDrawable drawable, int x, int y, int width, int height ) {
      GL2 gl = drawable.getGL().getGL2();
      if( height <= 0 )
         height = 1;
      final float h = ( float ) width/( float ) height;
      gl.glViewport( 0, 0, width, height );
      gl.glMatrixMode( GL2.GL_PROJECTION );
      gl.glLoadIdentity();
      glu.gluPerspective( 45.0f, h, 1.0, 20.0 );
      gl.glMatrixMode( GL2.GL_MODELVIEW );
      gl.glLoadIdentity();
   }
   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 );
      Line3d line3d = new Line3d();
      glcanvas.addGLEventListener( line3d );
      glcanvas.setSize( 400, 400 );
      //creating frame
      final JFrame frame = new JFrame (" 3d line");
      //adding canvas to it
      frame.getContentPane().add( glcanvas );
      frame.setSize(frame.getContentPane().getPreferredSize() );
      frame.setVisible( true );
   }//end of main
}//end of class

编译并执行上述程序时，会生成以下输出 -

3D线

可以通过给glVertex3f()方法的z象限赋予非零值来绘制3D形状，从而生成上述视图。 现在加入剩余的线将导致3D边缘。

现在以同样的方式让我们开发出第三维的优势。

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.media.opengl.glu.GLU;
import javax.swing.JFrame;
public class Edge1 implements GLEventListener {
   private GLU glu = new GLU();
   @Override
   public void display(GLAutoDrawable drawable) {
      // TODO Auto-generated method stub
      final GL2 gl = drawable.getGL().getGL2();
      gl.glTranslatef(0f, 0f, -2.5f);
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f(-0.75f,0f,0);
      gl.glVertex3f(0f,-0.75f, 0);
      gl.glEnd();
      //3d line
      gl.glBegin(GL2.GL_LINES);
      //3 units in to the window
      gl.glVertex3f(-0.75f,0f,3f);
      gl.glVertex3f(0f,-0.75f,3f);
      gl.glEnd();
      //top
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f(-0.75f,0f,0);
      gl.glVertex3f(-0.75f,0f,3f);
      gl.glEnd();
      //bottom
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f(0f,-0.75f, 0);
      gl.glVertex3f(0f,-0.75f,3f);
      gl.glEnd();
   }
   @Override
   public void dispose(GLAutoDrawable arg0) {
      //method body
   }
   @Override
   public void init(GLAutoDrawable arg0) {
      // method body
   }
   @Override
   public void reshape(GLAutoDrawable drawable, int x, int y, int width, int height) {
      // TODO Auto-generated method stubfinal
      GL2 gl = drawable.getGL().getGL2();
      if(height <= 0)
         height = 1;
      final float h = (float) width/(float) height;
      gl.glViewport(0, 0, width, height);
      gl.glMatrixMode(GL2.GL_PROJECTION);
      gl.glLoadIdentity();
      glu.gluPerspective(45.0f, h, 1.0, 20.0);
      gl.glMatrixMode(GL2.GL_MODELVIEW);
      gl.glLoadIdentity();
   }
   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);
      Edge1 b = new Edge1();
      glcanvas.addGLEventListener(b);
      glcanvas.setSize(400, 400);
      //creating frame
      final JFrame frame = new JFrame (" 3d edge");
      //adding canvas to it
      frame.getContentPane().add(glcanvas);
      frame.setSize(frame.getContentPane().getPreferredSize());
      frame.setVisible(true);
   }//end of main
}//end of class

编译并执行上述程序时，会生成以下输出 -

3D边缘

以同样的方式，通过将3D边缘开发到任何2D四边形的相应边并连接相邻顶点，您可以获得3D四边形。

下面给出了一个使用JOGL绘制菱形的程序。

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.media.opengl.glu.GLU;
import javax.swing.JFrame;
public class Rhombus implements GLEventListener {
   private GLU glu = new GLU();
   @Override
   public void display(GLAutoDrawable drawable) {
      final GL2 gl = drawable.getGL().getGL2();
      gl.glTranslatef(0f, 0f, -2.5f);
      //drawing edge1.....
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f(-0.75f,0f,0);
      gl.glVertex3f(0f,-0.75f, 0);
      gl.glEnd();
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f(-0.75f,0f,3f); // 3 units into the window
      gl.glVertex3f(0f,-0.75f,3f);
      gl.glEnd();
      //top
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f(-0.75f,0f,0);
      gl.glVertex3f(-0.75f,0f,3f);
      gl.glEnd();
      // bottom
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f(0f,-0.75f, 0);
      gl.glVertex3f(0f,-0.75f,3f);
      gl.glEnd();
      // edge 2....
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f(0f,-0.75f, 0);
      gl.glVertex3f(0.75f,0f, 0);
      gl.glEnd();
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f(0f,-0.75f, 3f);
      gl.glVertex3f(0.75f,0f, 3f);
      gl.glEnd();
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f(0f,-0.75f, 0);
      gl.glVertex3f(0f,-0.75f, 3f);
      gl.glEnd();
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f(0.75f,0f, 0);
      gl.glVertex3f(0.75f,0f, 3f);
      gl.glEnd();
      //Edge 3.............
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f( 0.0f,0.75f,0);
      gl.glVertex3f(-0.75f,0f,0);
      gl.glEnd();
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f( 0.0f,0.75f,3f);
      gl.glVertex3f(-0.75f,0f,3f);
      gl.glEnd();
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f( 0.0f,0.75f,0);
      gl.glVertex3f( 0.0f,0.75f,3f);
      gl.glEnd();
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f(-0.75f,0f,0);
      gl.glVertex3f(-0.75f,0f,3f);
      gl.glEnd();
      //final edge
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f(0.75f,0f, 0);
      gl.glVertex3f( 0.0f,0.75f,0);
      gl.glEnd();
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f(0.75f,0f,3f);
      gl.glVertex3f( 0.0f,0.75f,3f);
      gl.glEnd();
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f(0.75f,0f, 0);
      gl.glVertex3f(0.75f,0f,3f);
      gl.glEnd();
      gl.glBegin(GL2.GL_LINES);
      gl.glVertex3f( 0.0f,0.75f,0);
      gl.glVertex3f( 0.0f,0.75f,3f);
      gl.glEnd();
   }
   @Override
   public void dispose(GLAutoDrawable arg0) {
      //method body
   }
   @Override
   public void init(GLAutoDrawable arg0) {
      // method body
   }
   @Override
   public void reshape(GLAutoDrawable drawable, int x, int y, int width, int height) {
      // TODO Auto-generated method stub final
      GL2 gl = drawable.getGL().getGL2();
      if(height lt;= 0)
         height = 1;
      final float h = (float) width/(float) height;
      gl.glViewport(3, 6, width, height);
      gl.glMatrixMode(GL2.GL_PROJECTION);
      gl.glLoadIdentity();
      glu.gluPerspective(45.0f, h, 1.0, 20.0);
      gl.glMatrixMode(GL2.GL_MODELVIEW);
      gl.glLoadIdentity();
   }
   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);
      Rhombus b = new Rhombus();
      glcanvas.addGLEventListener(b);
      glcanvas.setSize(400, 400);
      //creating frame
      final JFrame frame = new JFrame (" Rhombus 3d");
      //adding canvas to it
      frame.getContentPane().add(glcanvas);
      frame.setSize(frame.getContentPane().getPreferredSize());
      frame.setVisible(true);
   }//end of main
}//end of classimport javax.media.opengl.GL2;

编译并执行上述程序时，将生成以下输出。 它显示使用3D线条绘制的菱形。

菱形3D

glBegin()方法的预定义参数可用于绘制3D形状。

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