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

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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*);
vbb.order(ByteOrder.nativeOrder());
FloatBuffer vertex = vbb.asFloatBuffer();
vertex.put(vertexArray);
vertex.position(); gl.glLoadIdentity();
gl.glTranslatef(, , -); gl.glEnableClientState(GL10.GL_VERTEX_ARRAY); gl.glVertexPointer(, GL10.GL_FLOAT, , vertex);
index++;
index%=;
switch(index){
case :
case :
case :
gl.glColor4f(1.0f, 0.0f, 0.0f, 1.0f);
gl.glDrawArrays(GL10.GL_LINES, , );
break;
case :
case :
case :
gl.glColor4f(0.0f, 1.0f, 0.0f, 1.0f);
gl.glDrawArrays(GL10.GL_LINE_STRIP, , );
break;
case :
case :
case :
case :
gl.glColor4f(0.0f, 0.0f, 1.0f, 1.0f);
gl.glDrawArrays(GL10.GL_LINE_LOOP, , );
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*);
vbb.order(ByteOrder.nativeOrder());
FloatBuffer vertex = vbb.asFloatBuffer();
vertex.put(vertexArray);
vertex.position(); gl.glLoadIdentity();
gl.glTranslatef(, , -); gl.glEnableClientState(GL10.GL_VERTEX_ARRAY); gl.glVertexPointer(, GL10.GL_FLOAT, , vertex);
int index = ;
index ++;
index%=;
switch(index){
case :
case :
case :
gl.glColor4f(1.0f, 0.0f, 0.0f, 1.0f);
gl.glDrawArrays(GL10.GL_LINES, , );
break;
case :
case :
case :
gl.glColor4f(0.0f, 1.0f, 0.0f, 1.0f);
gl.glDrawArrays(GL10.GL_LINE_STRIP, , );
break;
case :
case :
case :
case :
gl.glColor4f(0.0f, 0.0f, 1.0f, 1.0f);
gl.glDrawArrays(GL10.GL_LINE_LOOP, , );
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(, , 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 }
}