Android的OpenGL学习笔记（3）

 为了验证我们以前在旋转三角形的时候，到底是在旋转三角形本身，还是在旋转场景，现在用下面的实例代码验证，就会一目了然了：

MainActivity和前面的MainActivity一样，主要区别在继承GLSurfaceView.Renderer这段代码：

VortexRenderer.java代码：

package com.droidnova.android.games.vortex;

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.class.getSimpleName();

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

    // a raw buffer to hold indices allowing a reuse of points.
    private ShortBuffer _indexBuffer;
    private ShortBuffer _indexBufferStatic;

    // a raw buffer to hold the vertices
    private FloatBuffer _vertexBuffer;
    private FloatBuffer _vertexBufferStatic;

    private short[] _indicesArray = {0, 1, 2};
    private int _nrOfVertices = 3;

    private float _angle;

    @Override
    public void onSurfaceCreated(GL10 gl, EGLConfig config) {
        // preparation
        gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
        initTriangle();
        initStaticTriangle();
    }

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

    public void setAngle(float angle) {
        _angle = angle;
    }

    @Override
    public void onDrawFrame(GL10 gl) {
        // define the color we want to be displayed as the "clipping wall"
        gl.glClearColor(_red, _green, _blue, 1.0f);

        // reset the matrix - good to fix the rotation to a static angle
        gl.glLoadIdentity();

        // clear the color buffer to show the ClearColor we called above...
        gl.glClear(GL10.GL_COLOR_BUFFER_BIT);

        // draw the static triangle
        gl.glColor4f(0.5f, 0f, 0f, 0.5f);
        gl.glVertexPointer(3, GL10.GL_FLOAT, 0, _vertexBuffer);
        //第三个参数表示在数组元素中，两个有意义的数据单元之间相隔的字节数。
        //当值为0时，表示该数组数据是紧密排列的，没有间隔
        gl.glDrawElements(GL10.GL_TRIANGLES, _nrOfVertices, GL10.GL_UNSIGNED_SHORT, _indexBuffer);
        //gl.glDrawArrays(mode, first, count);
        // set rotation for the non-static triangle
        gl.glRotatef(_angle, 0f, 1f, 0f);

        gl.glColor4f(0f, 0.5f, 0f, 0.5f);
        gl.glVertexPointer(3, GL10.GL_FLOAT, 0, _vertexBufferStatic);
        gl.glDrawElements(GL10.GL_TRIANGLES, _nrOfVertices, GL10.GL_UNSIGNED_SHORT, _indexBufferStatic);

    }

    private void initTriangle() {
        // float has 4 bytes
        ByteBuffer vbb = ByteBuffer.allocateDirect(_nrOfVertices * 3 * 4);//对于每个顶点的位置，由x,y,z3个float分量组成，每个float占4个字节
        //因此申请的总长度为_nrOfVertices * 3 * 4,必须要使用allocateDirect.
        vbb.order(ByteOrder.nativeOrder());//必须要设置为原生字节序
        _vertexBuffer = vbb.asFloatBuffer();

        // short has 2 bytes
        ByteBuffer ibb = ByteBuffer.allocateDirect(_nrOfVertices * 2);//同上
        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);
    }

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

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

        float[] coords = {
            -0.4f, -0.4f, 0f, // (x1, y1, z1)
            0.4f, -0.4f, 0f, // (x2, y2, z2)
            0f, 0.4f, 0f // (x3, y3, z3)
        };

        _vertexBufferStatic.put(coords);

        _indexBufferStatic.put(_indicesArray);

        _vertexBufferStatic.position(0);
        _indexBufferStatic.position(0);
    }

    public void setColor(float r, float g, float b) {
        _red = r;
        _green = g;
        _blue = b;
    }
}

VortexView.java代码：

package com.droidnova.android.games.vortex;

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

public class VortexView extends GLSurfaceView {
    // private static final String LOG_TAG = VortexView.class.getSimpleName();
    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);
                _renderer.setAngle(event.getX());
            }
        });
        return true;
    }
}

运行结果：