3D画一个圆

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大家要知道GLSurfaceview里面没有像2D里面的drawCircle(x,y,r,paint);的函数，所以得想到其他的方法了。

画圆就是根据R*R=R*RCOS^2+R*RSIN^2;循环N次，这样就可以得到N个点，点点之间都是直线，所以点越多，圆越圆。下面让我们看看代码吧。

package wyf.lgz;

import android.app.Activity;
import android.content.pm.ActivityInfo;
import android.os.Bundle;
import android.view.Window;
import android.view.WindowManager;

public class Activity_GL_Cylinder extends Activity {
private MyGLSurfaceView mGLSurfaceView;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
        setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);

        mGLSurfaceView = new MyGLSurfaceView(this);
        setContentView(mGLSurfaceView);
        mGLSurfaceView.setFocusableInTouchMode(true);//设置为可触控
        mGLSurfaceView.requestFocus();//获取焦点
    }

    @Override
    protected void onResume() {
        super.onResume();
        mGLSurfaceView.onResume();
    }

    @Override
    protected void onPause() {
        super.onPause();
        mGLSurfaceView.onPause();
    }
}

package wyf.lgz;
import android.opengl.GLSurfaceView;
import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;
import android.content.Context;
import android.view.MotionEvent;

public class MyGLSurfaceView extends GLSurfaceView {
    private final float TOUCH_SCALE_FACTOR = 180.0f/320;//角度缩放比例
    private SceneRenderer mRenderer;//场景渲染器
    private float mPreviousY;//上次的触控位置Y坐标
    private float mPreviousX;//上次的触控位置Y坐标

public MyGLSurfaceView(Context context) {
        super(context);
        mRenderer = new SceneRenderer(); //创建场景渲染器
        setRenderer(mRenderer);    //设置渲染器
        setRenderMode(GLSurfaceView.RENDERMODE_CONTINUOUSLY);//设置渲染模式为主动渲染
    }

    //触摸事件回调方法
    @Override
    public boolean onTouchEvent(MotionEvent e) {
        float y = e.getY();
        float x = e.getX();
        switch (e.getAction()) {
        case MotionEvent.ACTION_MOVE:
            float dy = y - mPreviousY;//计算触控笔Y位移
            float dx = x - mPreviousX;//计算触控笔Y位移
            mRenderer.cylinder.mAngleX += dy * TOUCH_SCALE_FACTOR;//设置沿x轴旋转角度
            mRenderer.cylinder.mAngleZ += dx * TOUCH_SCALE_FACTOR;//设置沿z轴旋转角度
            requestRender();//重绘画面
        }
        mPreviousY = y;//记录触控笔位置
        mPreviousX = x;//记录触控笔位置
        return true;
    }

private class SceneRenderer implements GLSurfaceView.Renderer
    {
    DrawCylinder cylinder;//创建圆柱体

        public void onDrawFrame(GL10 gl) {
        //清除颜色缓存
        gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
        //设置当前矩阵为模式矩阵
            gl.glMatrixMode(GL10.GL_MODELVIEW);
            //设置当前矩阵为单位矩阵
            gl.glLoadIdentity();

            gl.glPushMatrix();//保护变换矩阵现场
            gl.glTranslatef(0, 0, -8f);//平移
            cylinder.drawSelf(gl);//绘制
            gl.glPopMatrix();//恢复变换矩阵现场
        }

        public void onSurfaceChanged(GL10 gl, int width, int height) {
            //设置视窗大小及位置
        gl.glViewport(0, 0, width, height);
        //设置当前矩阵为投影矩阵
            gl.glMatrixMode(GL10.GL_PROJECTION);
            //设置当前矩阵为单位矩阵
            gl.glLoadIdentity();
            //计算透视投影的比例
            float ratio = (float) width / height;
            //调用此方法计算产生透视投影矩阵
            gl.glFrustumf(-ratio, ratio, -1, 1, 1, 100);
        }

        public void onSurfaceCreated(GL10 gl, EGLConfig config) {
            //关闭抗抖动
        gl.glDisable(GL10.GL_DITHER);
        //设置特定Hint项目的模式，这里为设置为使用快速模式
            gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT,GL10.GL_FASTEST);
            //设置屏幕背景色白色RGBA
            gl.glClearColor(1,1,1,1);
            //设置着色模型为平滑着色
            gl.glShadeModel(GL10.GL_SMOOTH);
            //启用深度测试
            gl.glEnable(GL10.GL_DEPTH_TEST);

            cylinder=new DrawCylinder(10f,2f,1f,5);//创建圆柱体

}
}
}

package wyf.lgz;

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

import javax.microedition.khronos.opengles.GL10;

public class DrawCylinder
{
private FloatBuffer myVertexBuffer;//顶点坐标缓冲

int vCount;//顶点数量

float length;//圆柱长度
float circle_radius;//圆截环半径
float degreespan; //圆截环每一份的度数大小
int col;//圆柱块数

public float mAngleX;
public float mAngleY;
public float mAngleZ;

public DrawCylinder(float length,float circle_radius,float degreespan,int col)
{
  this.circle_radius=circle_radius;
  this.length=length;
  this.col=col;
  this.degreespan=degreespan;

  float collength=(float)length/col;//圆柱每块所占的长度

  ArrayList<Float> val=new ArrayList<Float>();//顶点存放列表

  for(float circle_degree=360.0f;circle_degree>0.0f;circle_degree-=degreespan)//循环行
  {
   int j=0;
   //for(int j=0;j<col;j++)//循环列
   {
    float x1 =(float)(j*collength-length/2);
    float y1=(float) (circle_radius*Math.sin(Math.toRadians(circle_degree)));
    float z1=(float) (circle_radius*Math.cos(Math.toRadians(circle_degree)));



    val.add(x1);val.add(y1);val.add(z1);//每条线两个顶点确定，有6条线，共12个顶点。

   }
  }

  vCount=val.size()/3;//确定顶点数量

  //顶点
  float[] vertexs=new float[vCount*3];
  for(int i=0;i<vCount*3;i++)
  {
   vertexs[i]=val.get(i);
  }
  ByteBuffer vbb=ByteBuffer.allocateDirect(vertexs.length*4);
  vbb.order(ByteOrder.nativeOrder());
  myVertexBuffer=vbb.asFloatBuffer();
  myVertexBuffer.put(vertexs);
  myVertexBuffer.position(0);
}

public void drawSelf(GL10 gl)
{
  gl.glRotatef(mAngleX, 1, 0, 0);//旋转
  gl.glRotatef(mAngleY, 0, 1, 0);
  gl.glRotatef(mAngleZ, 0, 0, 1);

  gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);//打开顶点缓冲
  gl.glVertexPointer(3, GL10.GL_FLOAT, 0, myVertexBuffer);//指定顶点缓冲

  gl.glColor4f(0, 0, 0, 0);//设置绘制线为黑色
  gl.glDrawArrays(GL10.GL_LINE_LOOP, 0, vCount);//绘制图像

  gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
}
}