Android 中使用OpenGL ES进行2D开发（纹理Texture使用）

OpenGL纹理是一种位图，可以把它粘贴到OpenGL物体的表面上。比如可以获取一张邮票的图像粘贴到正方形中，使正方形看起来像一张邮票。要使邮票保持合适的方向，以便图像井然有序地排列，则必须获得形状的每个顶点并在正方形上标记出来，以便邮票和正方形的形状保持一致。在OpenGL中引入了纹理坐标。

OpenGL 假设纹理图始终为1x1的正方形，其原点位于(0.0)处，右下角为(1,1)。如下图。

纹理坐标与顶点坐标之间的映射如下图：

所以我们用的浮点数组不只是要存储4个点的位置，还要存储纹理坐标值
vertices.put( new float[] {   -80f,   -120f, 0.0f, 1.0f ,

                                           80f,   -120f, 1.0f, 1.0f ,

                                           -80f, 120f, 0.0f, 0.0f ,

                                            80f,  120f,  1.0f,  0.0f });
处理完纹理坐标与顶点坐标之间的映射关系后，剩余工作包括将纹理位图加载到内存，为它分配纹理ID，以便重用此纹理。
来看下完整代码吧，注意我们代码中纹理坐标和顶点坐标分开存放了，这样更加清晰点，不然还要stride(跳过)内存。

package com.waitingfy.android.glbasics;

import java.io.IOException;
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.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.opengl.GLSurfaceView;
import android.opengl.GLUtils;
import android.opengl.GLSurfaceView.Renderer;
import android.os.Bundle;
import android.util.Log;
import android.view.Window;
import android.view.WindowManager;


public class TexturedRectangleTest extends Activity {
	public GLSurfaceView glView;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		// 去掉activity的标题，全屏显示
		requestWindowFeature(Window.FEATURE_NO_TITLE);
		getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
				WindowManager.LayoutParams.FLAG_FULLSCREEN);
		glView = new GLSurfaceView(this);
		glView.setRenderer(new SimpleRenderer());
		setContentView(glView);
	}

	@Override
	public void onResume() {
		super.onPause();
		glView.onResume();
	}

	@Override
	public void onPause() {
		super.onPause();
		glView.onPause();
	}

	class SimpleRenderer implements Renderer {

		FloatBuffer vertices;
		FloatBuffer texture;
		ShortBuffer indices;
		int textureId;

		public SimpleRenderer() {

			ByteBuffer byteBuffer = ByteBuffer.allocateDirect(4 * 2 * 4);
            byteBuffer.order(ByteOrder.nativeOrder());            
            vertices = byteBuffer.asFloatBuffer();
//            vertices.put( new float[] {  -80f,   -120f,0,1f,
//                                         80f,  -120f, 1f,1f,
//                                         -80f, 120f, 0f,0f,
//                                         80f,120f,   1f,0f});
            vertices.put( new float[] {  -80f,   -120f,
                                         80f,  -120f, 
                                         -80f, 120f,
                                         80f,  120f});
            
            ByteBuffer indicesBuffer = ByteBuffer.allocateDirect(6 * 2);
            indicesBuffer.order(ByteOrder.nativeOrder()); 
            indices = indicesBuffer.asShortBuffer();
            indices.put(new short[] { 0, 1, 2,1,2,3});
            
            ByteBuffer textureBuffer = ByteBuffer.allocateDirect(4 * 2 * 4);
            textureBuffer.order(ByteOrder.nativeOrder());            
            texture = textureBuffer.asFloatBuffer();
            texture.put( new float[] { 0,1f,
                                        1f,1f,
                                        0f,0f,
                                        1f,0f});
            
            indices.position(0);
            vertices.position(0);
            texture.position(0);
            
		}

		@Override
		public void onSurfaceCreated(GL10 gl, EGLConfig config) {
			Log.d("GLSurfaceViewTest", "surface created");
		}

		@Override
		public void onSurfaceChanged(GL10 gl, int width, int height) {
			Log.d("GLSurfaceViewTest", "surface changed: " + width + "x"
					+ height);
		}

		@Override
		public void onDrawFrame(GL10 gl) {
			textureId = loadTexture("bobrgb888.png",gl);
			//定义显示在屏幕上的什么位置(opengl 自动转换)
			gl.glViewport(0, 0, glView.getWidth(), glView.getHeight());
			gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
			gl.glMatrixMode(GL10.GL_PROJECTION);
			gl.glLoadIdentity();
			gl.glOrthof(-160, 160, -240, 240, 1, -1);

			gl.glEnable(GL10.GL_TEXTURE_2D);
                        //绑定纹理ID
                        gl.glBindTexture(GL10.GL_TEXTURE_2D, textureId);

			gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
			gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);

			gl.glVertexPointer(2, GL10.GL_FLOAT, 0, vertices);

			gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, texture);
			// gl.glRotatef(1, 0, 1, 0);
			gl.glDrawElements(GL10.GL_TRIANGLE_STRIP, 6,
					GL10.GL_UNSIGNED_SHORT, indices);
		}

		public int loadTexture(String fileName,GL10 gl) {
			try {
				Bitmap bitmap = BitmapFactory.decodeStream(getAssets().open(
						fileName));
				int textureIds[] = new int[1];
				gl.glGenTextures(1, textureIds, 0);
				int textureId = textureIds[0];
				gl.glBindTexture(GL10.GL_TEXTURE_2D, textureId);
				GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, bitmap, 0);
				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_NEAREST);
				gl.glBindTexture(GL10.GL_TEXTURE_2D, 0);
				bitmap.recycle();
				return textureId;
			} catch (IOException e) {
				Log.d("TexturedRectangleTest",
						"couldn't load asset 'bobrgb888.png'!");
				throw new RuntimeException("couldn't load asset '" + fileName
						+ "'");
			}
		}
	}
}

注意下我们这里用到的图片"bobrgb888.png"是png格式，存放在/assets/下，长宽是128*128，好像纹理图片最好是2的n次方大小，而且是正方形。

原文链接： http://www.waitingfy.com/?p=66

源码下载 gl-basics