opengl开发----2.画一个三角形

参考,这是一位德国人Martin写的文章,年代比较久远了.但是入门还是比较好的
1. 工程的建立
eclipse --> 新建一项目  com.example.gldemo
SDK 都选API 19: android 4.4 (KitKat)


2. MainActivity.java  -->跟以前一样

package com.example.gldemo;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;

public class MainActivity extends Activity {
    private VortexView _vortexView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        _vortexView = new VortexView(this);
        setContentView(_vortexView);
        //setContentView(R.layout.activity_main);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

VortexView.java-->跟以前一样

package com.example.gldemo;

import android.content.Context;
import android.opengl.GLSurfaceView;
import android.view.MotionEvent;

public class VortexView extends GLSurfaceView{
    private static final String LOG_TAG="VortexView";
    private VortexRenderer _renderer;
    public VortexView (Context context){
        super(context);
        _renderer = new VortexRenderer();
        setRenderer(_renderer);
    }

    public boolean onTouchEvent(final MotionEvent event){
        queueEvent(new Runnable(){
            public void run(){
                _renderer.setColor(event.getX()/getWidth(),
                                 event.getY()/getHeight(), 1.0f);
            }
        });
        return true;
    }
}

VortexRenderer.java

package com.example.gldemo;

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;

public class VortexRenderer implements GLSurfaceView.Renderer {
    private static final String LOG_TAG="VortexRenderer";
    private float _red = 0.9f;
    private float _green = 0.9f;
    private float _blue = 0.9f;
    //use for initTriangle
    private ShortBuffer _indexBuffer;          -->三角形的索引
    private FloatBuffer _vertexBuffer;         -->三角形的坐标
    private short[] _indicesArray = {0, 1, 2};
    private int _nrOfVertices = 3;             -->三角形的顶点数为3个
    @Override
    public void onSurfaceCreated(GL10 gl, EGLConfig config) {
        // TODO Auto-generated method stub
        gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);    -->设置opengl使用vertex数组来画
        initTriangle();                                  -->初始化vertex数组
    }

    @Override
    public void onSurfaceChanged(GL10 gl, int w, int h){
        gl.glViewport(0, 0, w, h);
    }

    @Override
    public void onDrawFrame(GL10 gl ){
        gl.glClearColor(_red, _green, _blue, 1.0f);         -->用定义的rgb来设设置背景色
        gl.glClear(GL10.GL_COLOR_BUFFER_BIT);               -->清空buffer
        gl.glColor4f(0.5f, 0f,    0f, 0.5f);                -->设置绘制三角形的颜色
        //设置顶点: 3代表三维,GL_FLOAT代表buffer里面是float,0代表没有offset,_vertexBuffer是存放顶点坐标的buffer
        gl.glVertexPointer(3, GL10.GL_FLOAT, 0, _vertexBuffer);
        //画:GL_TRIANGLES代表要画三角形,_nrOfVertices代表一个三角形三个顶点,GL_UNSIGNED_SHORT是type,_indexBuffer指向索引存贮位置的指针
        gl.glDrawElements(GL10.GL_TRIANGLES, _nrOfVertices, GL10.GL_UNSIGNED_SHORT, _indexBuffer);
    }
    public void setColor(float r, float g, float b) {
        _red = r;
        _green = g;
        _blue = b;
    }
    private void initTriangle(){
        //ByteBuffer vbb = ByteBuffer.allocate(_nrOfVertices*3*4);
        ByteBuffer vbb = ByteBuffer.allocateDirect(_nrOfVertices*3*4);   -->这儿要用allocateDirect方法
        vbb.order(ByteOrder.nativeOrder());
        _vertexBuffer = vbb.asFloatBuffer();

        //ByteBuffer ibb = ByteBuffer.allocate(_nrOfVertices*3*4);
        ByteBuffer ibb = ByteBuffer.allocateDirect(_nrOfVertices*3*4);
        ibb.order(ByteOrder.nativeOrder());
        _indexBuffer = ibb.asShortBuffer();

        float [] coords = {
                -0.5f, -0.5f, 0f,
                0.5f, -0.5f, 0f,
                0.0f, 0.5f, 0f
        };

        _vertexBuffer.put(coords);
        _indexBuffer.put(_indicesArray);
        _vertexBuffer.position(0);
        _indexBuffer.position(0);
    }
}

注意:原文中使用了ByteBuffer.allocate,但是这个方法现在不能使用了,会报以下错误
E/AndroidRuntime( 6951): java.lang.IllegalArgumentException: Must use a native order direct Buffer
替换为allocateDirect就可以了

3. 按屏幕后出现一个旋转的三角形
glDemo1.rar(下载后不用改名)
在VortexRenderer.java中的onDrawFrame

public void onDrawFrame(GL10 gl ){
        gl.glClearColor(_red, _green, _blue, 1.0f);
        gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
        gl.glRotatef(_angle, 0f, 1f, 0f);
        gl.glColor4f(0.5f, 0f,    0f, 0.5f);
        gl.glVertexPointer(3, GL10.GL_FLOAT, 0, _vertexBuffer);
        gl.glDrawElements(GL10.GL_TRIANGLES, _nrOfVertices, GL10.GL_UNSIGNED_SHORT, _indexBuffer);
    }