Android OpenGL学习笔记(二)之----三角形的绘制.

 

前面讲了一些Android OpenGl 的概念问题，这一节讲给大家讲一下如何画一个三角现出来.

 

一、新建一个Android工程命名为:OpenGL_Lesson2.

 

二、修改OpenGL_Lesson2.java代码如下:

package com.android.tutor;
import android.app.Activity;
import android.os.Bundle;
public class OpenGL_Lesson2 extends Activity {

    private OpenGlView mOpenGlView;
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mOpenGlView = new OpenGlView(this);
        setContentView(mOpenGlView);

    }
}

 

三、新建一个类OpenGlView.java继承与GLSurfaceView,代码如下:

package com.android.tutor;
import android.content.Context;
import android.opengl.GLSurfaceView;
public class OpenGlView extends GLSurfaceView {

    private OpenGlRender mOpenGlRender;
    public OpenGlView(Context context) {
        super(context);
        mOpenGlRender = new OpenGlRender();
        setRenderer(mOpenGlRender);
    }



}

 

四、新建一个OpenGlRender.java类继承与Renderer,代码如下:

 

package com.android.tutor;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;
import java.nio.ShortBuffer;
import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;
import android.opengl.GLSurfaceView.Renderer;
public class OpenGlRender implements Renderer {

    private float _red = 0f;
    private float _green = 25f;
    private float _blue = 200f;

    private ShortBuffer _indexBuffer;

    private FloatBuffer _vertexBuffer;


    private short[] _indicesArray = {0, 1, 2};
    private int _nrOfVertices = 3;
    @Override
    public void onSurfaceCreated(GL10 gl, EGLConfig config) {

        gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
        initTriangle();
    }
    @Override
    public void onSurfaceChanged(GL10 gl, int width, int height) {

        gl.glViewport(0, 0, width, height);
    }


    @Override
    public void onDrawFrame(GL10 gl) {
        gl.glClearColor(_red, _green, _blue, 1.0f);

        gl.glClear(GL10.GL_COLOR_BUFFER_BIT);

         gl.glColor4f(0.5f, 0f, 0f, 0.5f);
         gl.glVertexPointer(_nrOfVertices, GL10.GL_FLOAT, 0, _vertexBuffer);
         gl.glDrawElements(GL10.GL_TRIANGLES, _nrOfVertices, GL10.GL_UNSIGNED_SHORT, _indexBuffer);
    }

    private void initTriangle() {
        // float has 4 bytes
        ByteBuffer vbb = ByteBuffer.allocateDirect(_nrOfVertices * 3 * 4);
        vbb.order(ByteOrder.nativeOrder());
        _vertexBuffer = vbb.asFloatBuffer();

        // short has 4 bytes
        ByteBuffer ibb = ByteBuffer.allocateDirect(_nrOfVertices * 2);
        ibb.order(ByteOrder.nativeOrder());
        _indexBuffer = ibb.asShortBuffer();

        float[] coords = {
            -0.5f, -0.5f, 0f, // (x1, y1, z1)
            0.5f, -0.5f, 0f, // (x2, y2, z2)
            0f, 0.5f, 0f // (x3, y3, z3)
        };

        _vertexBuffer.put(coords);

        _indexBuffer.put(_indicesArray);

        _vertexBuffer.position(0);
        _indexBuffer.position(0);
    }
}

 

五、运行之，效果如下:

 

vertexBuffer 定义每个顶点的位置； indexBuffer 定义三角形中顶点在 vertextBuffer 中的索引。使用 indexBuffer 和 vertextBuffer 可以节省空间（因为可重复利用 vertex ）。