上一篇讲了基础入门  ，这一次主要学习OpenGL 纹理基本学习总结

要是做复杂的OpenGL应用程序，一定会用到纹理技术。纹理说白了就是把图片或者视频图像绘制到OpenGL空间中。

因此纹理也有坐标系，称ST坐标。或者UV

上面是纹理坐标空间。但没有固定的方向

以下演示载入一张image作为纹理贴图。

public class TextureUtils {	public static int createTexture(InputStream ins) {		int[] textures = new int[1];		GLES20.glGenTextures(1, textures, 0);//生成一个纹理						int textureId = textures[0];		GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textureId);		GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MIN_FILTER,GLES20.GL_NEAREST); 		GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D,GLES20.GL_TEXTURE_MAG_FILTER,GLES20.GL_LINEAR);		GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_S,GLES20.GL_CLAMP_TO_EDGE);		GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_T,GLES20.GL_CLAMP_TO_EDGE);		//上面是纹理贴图的取样方式，包含拉伸方式，取临近值和线性值		Bitmap bitmap = BitmapFactory.decodeStream(ins);		GLUtils.texImage2D(GLES20.GL_TEXTURE_2D, 0, bitmap, 0);//让图片和纹理关联起来。载入到OpenGl空间中		Log.d("OPENGL","bitmap:" + bitmap);		bitmap.recycle();//不须要。能够释放		return textureId;	}}

public class MyRenderer implements Renderer {	public static float[] projMatrix = new float[16];// 投影	public static float[] viewMatrix = new float[16];// 相机	public static float[] mViewPjMatrix;// 总变换矩阵	public static float[] matrixs = new float[16];	public static int textureId = -1;	Context context;	MyDrawModel drawModel;	public MyRenderer(Context context) {		this.context = context;	}	@Override	public void onDrawFrame(GL10 arg0) {		GLES20.glClear( GLES20.GL_DEPTH_BUFFER_BIT | GLES20.GL_COLOR_BUFFER_BIT);		Log.e("", "textureId:" + textureId);		drawModel.drawFrame(textureId);	}	@Override	public void onSurfaceChanged(GL10 arg0, int w, int h) {		GLES20.glViewport(0, 0, w, h);		float ratio = (float) w / h;		Matrix.frustumM(projMatrix, 0, -ratio, ratio, -1, 1, 1, 10);//投影矩阵设置		Matrix.setLookAtM(viewMatrix, 0, 0, 0, 3, 0, 0, 0, 0.0f, 1.0f, 0.0f);//摄像机坐标设置	}	@Override	public void onSurfaceCreated(GL10 g, EGLConfig eglConfig) {		GLES20.glClearColor(0.5f,0.5f,0.5f, 1.0f);  		GLES20.glEnable(GLES20.GL_DEPTH_TEST);		InputStream ins = null;		drawModel = new MyDrawModel();		drawModel.init();		try {			ins = context.getAssets().open("house.jpg");			textureId = TextureUtils.createTexture(ins);			Log.e("", "textureId:" + textureId);		} catch (IOException e) {			e.printStackTrace();		} finally {			try {				ins.close();			} catch (IOException e) {				e.printStackTrace();			}		}		GLES20.glDisable(GLES20.GL_CULL_FACE);	}}

public class MyDrawModel {	private int programId;	private int mVPMatrixHandle; // 总变换矩阵引用id	private int positionHandle; // 顶点位置id	private int texCoorHandle; // 顶点纹理坐标id	private FloatBuffer vertexBuffer;	private FloatBuffer texCoorBuffer;	public MyDrawModel() {	}	public void init() {		initData();		int vertexsharder = GLHelper.compileScript(GLES20.GL_VERTEX_SHADER,				GLScript.vertex2);		int fragmentsharder = GLHelper.compileScript(GLES20.GL_FRAGMENT_SHADER,				GLScript.fragment2);		programId = GLHelper.linkAttach(vertexsharder, fragmentsharder);		boolean isOK = GLHelper.checkProgram(programId);		positionHandle = GLES20.glGetAttribLocation(programId, "aPosition");		texCoorHandle = GLES20.glGetAttribLocation(programId, "aTexCoor");		mVPMatrixHandle = GLES20.glGetUniformLocation(programId, "uMVPMatrix");		Log.d("OPENGL", "positionHandle:" + positionHandle + ";texCoorHandle:"				+ texCoorHandle + ";mVPMatrixHandle:" + mVPMatrixHandle + ";"				+ isOK);	}	private void initData() {		//X,Y,Z,绘画的顶点		float vertices[] = new float[] {		           0,     0, 0,			   -1.8f, -1f, 0,			   1.8f, -1f, 0,			   1.8f,  1f, 0,			   -1.8f,  1f, 0,			   -1.8f, -1f, 0		   };		ByteBuffer vb = ByteBuffer.allocateDirect(vertices.length * 4);		vb.order(ByteOrder.nativeOrder());		vertexBuffer = vb.asFloatBuffer();		vertexBuffer.put(vertices);		vertexBuffer.position(0);		//纹理空间坐标 S,T		float texCoor[] = new float[] { 				0.5f, 0.5f,				0f,     1f,				1f,     1f,				1f,     0f,				0f,     0f,				0f,     1f 			};		ByteBuffer cb = ByteBuffer.allocateDirect(texCoor.length * 4);		cb.order(ByteOrder.nativeOrder());		texCoorBuffer = cb.asFloatBuffer();		texCoorBuffer.put(texCoor);		texCoorBuffer.position(0);	}	public void drawFrame(int textureId) {				 GLES20.glUseProgram(programId);		 		 // // 初始化矩阵		 Matrix.setRotateM(MyRenderer.matrixs, 0, 0, 1, 0, 0);		 Matrix.translateM(MyRenderer.matrixs, 0, 0, 0, 1);		 		 //矩阵转换 ,投影矩阵，摄像机矩阵。模型矩阵		 MyRenderer.mViewPjMatrix = new float[16];		 Matrix.multiplyMM(MyRenderer.mViewPjMatrix, 0, MyRenderer.viewMatrix,0, MyRenderer.matrixs, 0);		 Matrix.multiplyMM(MyRenderer.mViewPjMatrix, 0, MyRenderer.projMatrix,0, MyRenderer.mViewPjMatrix, 0);		 GLES20.glUniformMatrix4fv(mVPMatrixHandle, 1, false, MyRenderer.mViewPjMatrix, 0);				 GLES20.glVertexAttribPointer(positionHandle, 3, GLES20.GL_FLOAT, false, 3 * 4, vertexBuffer);		 GLES20.glVertexAttribPointer(texCoorHandle,  2, GLES20.GL_FLOAT, false, 2 * 4, texCoorBuffer);				 GLES20.glEnableVertexAttribArray(positionHandle);		 GLES20.glEnableVertexAttribArray(texCoorHandle);				 GLES20.glActiveTexture(GLES20.GL_TEXTURE0);		 GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textureId);		 GLES20.glDrawArrays(GLES20.GL_TRIANGLE_FAN, 0, 6);//六个定点，绘制三角形	}}

OpenGL须要把设备的坐标归一化到[-1,-1]空间中。所以这里涉及到矩阵相乘的理论，包含世界坐标，物体坐标，摄像机坐标的转换。以后会具体介绍。

public class GLScript {	public GLScript() {	}		public static final String vertex1 = "attribute vec4 mPosition;\n" +              "void main()\n" +              "{\n" +                  "gl_Position=mPosition;\n " +              "}\n";        public static final String fragment1 = "precision mediump float;\n" +              "uniform vec4 mColor;\n" +              "void main(){ gl_FragColor=mColor;\n}";          public static final String vertex2 = "uniform mat4 uMVPMatrix;\n"    		 + "attribute vec3 aPosition;\n"    		 + "attribute vec2 aTexCoor;\n"    		 + "varying vec2 vTextureCoord;\n"     		 + "void main() { \n"    		 + "gl_Position = uMVPMatrix * vec4(aPosition,1);\n"    		 + "vTextureCoord = aTexCoor;\n"     		 + "}\n"    		;        public static final String fragment2 = "precision mediump float;\n"    		+ "varying vec2 vTextureCoord;\n"    		+ "uniform sampler2D sTexture;\n"    		+ "void main() { \n"    		+ "vec2 coord =  vTextureCoord;\n"    		+ "coord.s =  coord.s * 0.5;\n" //事实上是去图像的一半，向量缩小了    		+ "gl_FragColor = texture2D(sTexture, coord); \n"    		+ "}\n"    		;}

coord.s =  coord.s * 0.5;

这样是取纹理图像的一半，显示到界面上也就是图片的前半部分内容

其他的工具类和上一篇文章一样。

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原图：

本文转自mfrbuaa博客园博客，原文链接：http://www.cnblogs.com/mfrbuaa/p/5095000.html，如需转载请自行联系原作者