android:GLSurfaceView绘制bitmap图片及glViewport调整的效果

首先看一下GLSurfaceView是怎样绘制的。正如android开发文档中描写叙述的那样，我们须要new一个GLSurfaceView对象，然后设置一个实现了Renderer接口的对象，我们须要写一个MyRender类，实现Renderer的方法等等。我们先看一下Activity的写法。它不须要一个布局文件，我们将GLSurfaceView对象作为activity的contentview就可以。例如以下：

package net.mobctrl.glsurfaceviewbmp;

import java.util.Random;

import android.annotation.SuppressLint;

import android.app.Activity;

import android.opengl.GLSurfaceView;

import android.os.Bundle;

import android.view.WindowManager;

/**

 *

 * @author Zheng Haibo

 * @web http://www.mobctrl.net

 *

 */

public class MainActivity extends Activity {

	private GLSurfaceView glView; // Use GLSurfaceView

	Random rnd = new Random();

	@SuppressLint("NewApi")

	@Override

	protected void onCreate(Bundle savedInstanceState) {

		super.onCreate(savedInstanceState);

		setTheme(android.R.style.Theme_Translucent_NoTitleBar);

		getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);

		glView = new GLSurfaceView(this); // Allocate a GLSurfaceView

		glView.setRenderer(new MyGLRenderer(this)); // Use a custom renderer

		glView.getAlpha();

		this.setContentView(glView); 

	}

	@Override

	protected void onPause() {

		super.onPause();

		glView.onPause();

	}

	@Override

	protected void onResume() {

		super.onResume();

		glView.onResume();

		android.provider.Settings.System.putInt(this.getContentResolver(),

				android.provider.Settings.System.SCREEN_BRIGHTNESS,

				rnd.nextInt(256));

	}

}

以下，我们主要看一下MyGLRender类的写法，它实现了Renderer接口，详细例如以下：

package net.mobctrl.glsurfaceviewbmp;

import java.util.Random;

import javax.microedition.khronos.opengles.GL10;

import android.content.Context;

import android.opengl.GLSurfaceView.Renderer;

import android.opengl.GLU;

/**

 * @date 2014年10月20日 下午2:49:17

 * @author Zheng Haibo

 * @Description: TODO

 */

public class MyGLRenderer implements Renderer {

	Context context; // Application's context

	Random r = new Random();

	//private Square square;

	private GLBitmap glBitmap;

	private int width = 0;

	private int height = 0;

	private long frameSeq = 0;

	private int viewportOffset = 0;

	private int maxOffset = 400;

	public MyGLRenderer(Context context) {

		this.context = context;

		//square = new Square();

		glBitmap = new GLBitmap();

	}

	@Override

	public void onSurfaceChanged(GL10 gl, int width, int height) {

		if (height == 0) { // Prevent A Divide By Zero By

			height = 1; // Making Height Equal One

		}

		this.width = width;

		this.height = height;

		gl.glViewport(0, 0, width, height); // Reset The

											// Current

		// Viewport

		gl.glMatrixMode(GL10.GL_PROJECTION); // Select The Projection Matrix

		gl.glLoadIdentity(); // Reset The Projection Matrix

		// Calculate The Aspect Ratio Of The Window

		GLU.gluPerspective(gl, 45.0f, (float) width / (float) height, 0.1f,

				100.0f);

		gl.glMatrixMode(GL10.GL_MODELVIEW); // Select The Modelview Matrix

		gl.glLoadIdentity();

	}

	/**

	 * 每隔16ms调用一次

	 */

	@Override

	public void onDrawFrame(GL10 gl) {

		gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);

		// Reset the Modelview Matrix

		gl.glLoadIdentity();

		gl.glTranslatef(0.0f, 0.0f, -5.0f); // move 5 units INTO the screen is

											// the same as moving the camera 5

											// units away

		// square.draw(gl);

		glBitmap.draw(gl);

		changeGLViewport(gl);

	}

	/**

	 * 通过改变gl的视角获取

	 *

	 * @param gl

	 */

	private void changeGLViewport(GL10 gl) {

		System.out.println("time=" + System.currentTimeMillis());

		frameSeq++;

		viewportOffset++;

		// The

		// Current

		if (frameSeq % 100 == 0) {// 每隔100帧，重置

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

			viewportOffset = 0;

		} else {

			int k = 4;

			gl.glViewport(-maxOffset + viewportOffset * k, -maxOffset

					+ viewportOffset * k, this.width - viewportOffset * 2 * k

					+ maxOffset * 2, this.height - viewportOffset * 2 * k

					+ maxOffset * 2);

		}

	}

	@Override

	public void onSurfaceCreated(GL10 gl,

			javax.microedition.khronos.egl.EGLConfig arg1) {

		glBitmap.loadGLTexture(gl, this.context);

		gl.glEnable(GL10.GL_TEXTURE_2D); // Enable Texture Mapping ( NEW )

		gl.glShadeModel(GL10.GL_SMOOTH); // Enable Smooth Shading

		gl.glClearColor(0.0f, 0.0f, 0.0f, 0.5f); // Black Background

		gl.glClearDepthf(1.0f); // Depth Buffer Setup

		gl.glEnable(GL10.GL_DEPTH_TEST); // Enables Depth Testing

		gl.glDepthFunc(GL10.GL_LEQUAL); // The Type Of Depth Testing To Do

		gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT, GL10.GL_NICEST);

	}

}

注意，这里主要实现了例如以下三个方法：onSurfaceCreated，onSurfaceChanged和onDrawFrame，当中，关键就是onDrawFrame方法，它的绘制机制是：1s的时间内，onDrawFrame方法会调用60次，大约每隔16ms调用一次。我们先看里面的glBitmap对象，changeGLViewport方法待会再说。

package net.mobctrl.glsurfaceviewbmp;

import java.nio.ByteBuffer;

import java.nio.ByteOrder;

import java.nio.FloatBuffer;

import javax.microedition.khronos.opengles.GL10;

import net.mobctrl.glsurfaceviewbmp.R;

import android.content.Context;

import android.graphics.Bitmap;

import android.graphics.BitmapFactory;

import android.opengl.GLUtils;

/**

 * @date 2014年10月20日 下午3:09:33

 * @author Zheng Haibo

 * @Description: TODO

 */

public class GLBitmap {

	private FloatBuffer textureBuffer; // buffer holding the texture coordinates

	private float texture[] = {

			// Mapping coordinates for the vertices

			0.0f, 1.0f, // top left (V2)

			0.0f, 0.0f, // bottom left (V1)

			1.0f, 1.0f, // top right (V4)

			1.0f, 0.0f // bottom right (V3)

	};

	private FloatBuffer vertexBuffer; // buffer holding the vertices

	private float vertices[] = { -1.0f, -1.0f, 0.0f, // V1 - bottom left

			-1.0f, 1.0f, 0.0f, // V2 - top left

			1.0f, -1.0f, 0.0f, // V3 - bottom right

			1.0f, 1.0f, 0.0f // V4 - top right

	};

	public GLBitmap() {

		ByteBuffer byteBuffer = ByteBuffer.allocateDirect(vertices.length * 4);

		byteBuffer.order(ByteOrder.nativeOrder());

		vertexBuffer = byteBuffer.asFloatBuffer();

		vertexBuffer.put(vertices);

		vertexBuffer.position(0);

		byteBuffer = ByteBuffer.allocateDirect(texture.length * 4);

		byteBuffer.order(ByteOrder.nativeOrder());

		textureBuffer = byteBuffer.asFloatBuffer();

		textureBuffer.put(texture);

		textureBuffer.position(0);

	}

	/** The texture pointer */

	private int[] textures = new int[1];

	public void loadGLTexture(GL10 gl, Context context) {

		// loading texture

		Bitmap bitmap = BitmapFactory.decodeResource(context.getResources(),

				R.drawable.plane_image);

		// generate one texture pointer

		gl.glGenTextures(1, textures, 0);

		// ...and bind it to our array

		gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[0]);

		// create nearest filtered texture

		gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MIN_FILTER,

				GL10.GL_NEAREST);

		gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MAG_FILTER,

				GL10.GL_LINEAR);

		// Use Android GLUtils to specify a two-dimensional texture image from

		// our bitmap

		GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, bitmap, 0);

		// Clean up

		bitmap.recycle();

	}

	public void draw(GL10 gl) {

		// bind the previously generated texture

		gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[0]);

		// Point to our buffers

		gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);

		gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);

		// Set the face rotation

		gl.glFrontFace(GL10.GL_CW);

		// Point to our vertex buffer

		gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer);

		gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, textureBuffer);

		// Draw the vertices as triangle strip

		gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, vertices.length / 3);

		// Disable the client state before leaving

		gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);

		gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY);

	}

}

从GLBitmap能够看出，我们首先须要载入一个图片资源，然后生成texture。在这里，特别说明一下changeGLViewport这种方法，假设在MyRender里面去掉这种方法，执行结果是，GLSurfaceView绘制出一张图片。加入这种方法以后，则是周期性得绘制一个由远到近的一个“动画”。注意，这样的动画，并没有改变图像本身，并且调整不通的视角产生的，因此效率非常高。它的原理，就像你拿一个相机，去拍摄墙壁上得一幅画，相机离画越来越近时，画面在放大，而墙壁本身并没有变化。

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android:GLSurfaceView绘制bitmap图片及glViewport调整的效果

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