Android OpenGL ES（九）绘制线段Line Segment .

创建一个DrawLine Activity，定义四个顶点：

float vertexArray[] = {
 -0.8f, -0.4f * 1.732f, 0.0f,
 -0.4f, 0.4f * 1.732f, 0.0f,
 0.0f, -0.4f * 1.732f, 0.0f,
 0.4f, 0.4f * 1.732f, 0.0f,
};

分别以三种模式GL_LINES，GL_LINE_STRIP，GL_LINE_LOOP 来绘制直线：

public void DrawScene(GL10 gl) {
 super.DrawScene(gl);
 
 ByteBuffer vbb
 = ByteBuffer.allocateDirect(vertexArray.length*4);
 vbb.order(ByteOrder.nativeOrder());
 FloatBuffer vertex = vbb.asFloatBuffer();
 vertex.put(vertexArray);
 vertex.position(0);
 
 gl.glLoadIdentity();
 gl.glTranslatef(0, 0, -4);
 
 gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
 
 gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertex);
 index++;
 index%=10;
 switch(index){
 case 0:
 case 1:
 case 2:
 gl.glColor4f(1.0f, 0.0f, 0.0f, 1.0f);
 gl.glDrawArrays(GL10.GL_LINES, 0, 4);
 break;
 case 3:
 case 4:
 case 5:
 gl.glColor4f(0.0f, 1.0f, 0.0f, 1.0f);
 gl.glDrawArrays(GL10.GL_LINE_STRIP, 0, 4);
 break;
 case 6:
 case 7:
 case 8:
 case 9:
 gl.glColor4f(0.0f, 0.0f, 1.0f, 1.0f);
 gl.glDrawArrays(GL10.GL_LINE_LOOP, 0, 4);
 break;
 }
 
 gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
 
}

这里index 的目的是为了延迟一下显示（更好的做法是使用固定时间间隔）。前面说过GLSurfaceView 的渲染模式有两种，一种是连续不断的更新屏幕，另一种为on-demand ，只有在调用requestRender() 在更新屏幕。 缺省为RENDERMODE_CONTINUOUSLY 持续刷新屏幕。

OpenGLDemos 使用的是缺省的RENDERMODE_CONTINUOUSLY持续刷新屏幕 ，因此Activity的drawScene 会不断的执行。本例中屏幕上顺序以红，绿，蓝色显示LINES, LINE_STRIP,LINE_LOOP。

完整代码：

MainActivity.java

package com.example.gltest;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;

import javax.microedition.khronos.opengles.GL10;

import android.opengl.GLSurfaceView;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.Window;
import android.view.WindowManager;

public class MainActivity extends Activity
       implements IOpenGLDemo{
    float vertexArray[] = {
             -0.8f, -0.4f * 1.732f, 0.0f,
             -0.4f, 0.4f * 1.732f, 0.0f,
             0.0f, -0.4f * 1.732f, 0.0f,
             0.4f, 0.4f * 1.732f, 0.0f,
            };

        /** Called when the activity is first created. */
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            this.requestWindowFeature(Window.FEATURE_NO_TITLE);
            getWindow()
             .setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                WindowManager.LayoutParams.FLAG_FULLSCREEN);
     
            mGLSurfaceView = new GLSurfaceView(this);
            mGLSurfaceView.setRenderer(new OpenGLRenderer(this));
            setContentView(mGLSurfaceView);
        }
     
//        public void DrawScene(GL10 gl) {
//            gl.glClearColor(1.0f, 0.0f, 0.0f, 0.0f);
//            // Clears the screen and depth buffer.
//            gl.glClear(GL10.GL_COLOR_BUFFER_BIT
//              | GL10.GL_DEPTH_BUFFER_BIT);
//     
//        }
        public void DrawScene(GL10 gl) {
             //super.DrawScene(gl);
             
             ByteBuffer vbb
             = ByteBuffer.allocateDirect(vertexArray.length*4);
             vbb.order(ByteOrder.nativeOrder());
             FloatBuffer vertex = vbb.asFloatBuffer();
             vertex.put(vertexArray);
             vertex.position(0);
             
             gl.glLoadIdentity();
             gl.glTranslatef(0, 0, -4);
             
             gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
             
             gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertex);
             int index = 0;
            index ++;
             index%=10;
             switch(index){
             case 0:
             case 1:
             case 2:
             gl.glColor4f(1.0f, 0.0f, 0.0f, 1.0f);
             gl.glDrawArrays(GL10.GL_LINES, 0, 4);
             break;
             case 3:
             case 4:
             case 5:
             gl.glColor4f(0.0f, 1.0f, 0.0f, 1.0f);
             gl.glDrawArrays(GL10.GL_LINE_STRIP, 0, 4);
             break;
             case 6:
             case 7:
             case 8:
             case 9:
             gl.glColor4f(0.0f, 0.0f, 1.0f, 1.0f);
             gl.glDrawArrays(GL10.GL_LINE_LOOP, 0, 4);
             break;
             }
             
             gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
             
            }
     
        @Override
        protected void onResume() {
            // Ideally a game should implement
            // onResume() and onPause()
            // to take appropriate action when the
            //activity looses focus
            super.onResume();
            mGLSurfaceView.onResume();
        }
     
        @Override
        protected void onPause() {
            // Ideally a game should implement onResume()
            //and onPause()
            // to take appropriate action when the
            //activity looses focus
            super.onPause();
            mGLSurfaceView.onPause();
        }
     
        private GLSurfaceView mGLSurfaceView;
     
    }

OpenGLRenderer.java

package com.example.drawpointer;

import javax.microedition.khronos.opengles.GL10;

import android.opengl.EGLConfig;
import android.opengl.GLSurfaceView.Renderer;
import android.opengl.GLU;

public class OpenGLRenderer implements Renderer {
     
     private final IOpenGLDemo openGLDemo;
     public OpenGLRenderer(IOpenGLDemo demo){
     openGLDemo=demo;
     }
     
     public void onSurfaceCreated(GL10 gl, EGLConfig config) {
     // Set the background color to black ( rgba ).
     gl.glClearColor(0.0f, 0.0f, 0.0f, 0.5f);
     // Enable Smooth Shading, default not really needed.
     gl.glShadeModel(GL10.GL_SMOOTH);
     // Depth buffer setup.
     gl.glClearDepthf(1.0f);
     // Enables depth testing.
     gl.glEnable(GL10.GL_DEPTH_TEST);
     // The type of depth testing to do.
     gl.glDepthFunc(GL10.GL_LEQUAL);
     // Really nice perspective calculations.
     gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT,
     GL10.GL_NICEST);
     
     }
     
     public void onDrawFrame(GL10 gl) {
     if(openGLDemo!=null){
     openGLDemo.DrawScene(gl);
     }
     
     }
     
     public void onSurfaceChanged(GL10 gl, int width, int height) {
     // Sets the current view port to the new size.
     gl.glViewport(0, 0, width, height);
     // Select the projection matrix
     gl.glMatrixMode(GL10.GL_PROJECTION);
     // Reset the projection matrix
     gl.glLoadIdentity();
     // Calculate the aspect ratio of the window
     GLU.gluPerspective(gl, 45.0f,
     (float) width / (float) height,
     0.1f, 100.0f);
     // Select the modelview matrix
     gl.glMatrixMode(GL10.GL_MODELVIEW);
     // Reset the modelview matrix
     gl.glLoadIdentity();
     }

    @Override
    public void onSurfaceCreated(GL10 arg0,
            javax.microedition.khronos.egl.EGLConfig arg1) {
        // TODO Auto-generated method stub
        
    }
    }

IOpenGLDemo.java

package com.example.gltest;

import javax.microedition.khronos.opengles.GL10;

public interface IOpenGLDemo {
     public void DrawScene(GL10 gl);
     
    }