上一篇讲了基础入门OpenGL (一)，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
下面演示加载一张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，包括拉伸方式，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，加载到OpenGl空间中Log.d("OPENGL","bitmap:" + bitmap);bitmap.recycle();//不需要，可以释放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;}@Overridepublic void onDrawFrame(GL10 arg0) {GLES20.glClear( GLES20.GL_DEPTH_BUFFER_BIT | GLES20.GL_COLOR_BUFFER_BIT);Log.e("", "textureId:" + textureId);drawModel.drawFrame(textureId);}@Overridepublic 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}@Overridepublic 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idprivate int positionHandle; // 顶点位置idprivate int texCoorHandle; // 顶点纹理坐标idprivate 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,Tfloat 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需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，包括世界坐标，物体坐标，摄像机坐标的转换，以后会详细介绍。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" //其实是去图像的一半，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
其它的工具类和上一篇文章一样。
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以后我会去到很多很繁华或苍凉，
