openGLeES 纹理贴图完整例子

下面是一个使用OpenGL ES 2.0进行纹理贴图的完整例子。该例子使用Android平台的Java语言进行编写，但是只要稍作修改，就可以用于其他平台的OpenGL ES 2.0开发。

在这个例子中，我们将使用一个简单的正方形作为我们的几何形状，并将一张图片作为纹理贴图。我们将使用着色器程序来将纹理映射到几何形状上。

1. 首先，我们需要定义一个顶点着色器程序，用于将顶点坐标和纹理坐标传递给渲染管线：

private static final String VERTEX_SHADER =
        "uniform mat4 uMVPMatrix;\n" +
        "attribute vec4 aPosition;\n" +
        "attribute vec2 aTextureCoord;\n" +
        "varying vec2 vTextureCoord;\n" +
        "void main() {\n" +
        "  gl_Position = uMVPMatrix * aPosition;\n" +
        "  vTextureCoord = aTextureCoord;\n" +
        "}\n";

2. 接下来，我们需要定义一个片段着色器程序，用于将纹理映射到几何形状上：

private static final String FRAGMENT_SHADER =
        "precision mediump float;\n" +
        "varying vec2 vTextureCoord;\n" +
        "uniform sampler2D uTextureSampler;\n" +
        "void main() {\n" +
        "  gl_FragColor = texture2D(uTextureSampler, vTextureCoord);\n" +
        "}\n";

3. 现在，我们需要定义一个顶点数组，用于存储正方形的顶点坐标和纹理坐标：

private static final float[] VERTEX_ARRAY = {
        // Vertex coordinates (x,y,z)
        -1f,  1f, 0f, // top left
         1f,  1f, 0f, // top right
        -1f, -1f, 0f, // bottom left
         1f, -1f, 0f, // bottom right

        // Texture coordinates (u,v)
        0f, 1f, // top left
        1f, 1f, // top right
        0f, 0f, // bottom left
        1f, 0f  // bottom right
};

4. 然后，我们需要创建一个顶点缓冲区，并将顶点数组数据传递给它：

private FloatBuffer vertexBuffer;
...
// initialize vertex buffer
ByteBuffer bb = ByteBuffer.allocateDirect(VERTEX_ARRAY.length * 4);
bb.order(ByteOrder.nativeOrder());
vertexBuffer = bb.asFloatBuffer();
vertexBuffer.put(VERTEX_ARRAY);
vertexBuffer.position(0);

5. 接下来，我们需要加载一张图片作为纹理，并将它绑定到OpenGL ES上下文中：

private int[] textures = new int[1]; // stores the texture IDs
...
// load texture
Bitmap textureBitmap = BitmapFactory.decodeResource(context.getResources(), R.drawable.texture);
GLES20.glGenTextures(1, textures, 0);
GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textures[0]);
GLUtils.texImage2D(GLES20.GL_TEXTURE_2D, 0, textureBitmap, 0);
textureBitmap.recycle();

6. 然后，我们需要定义一个着色器程序，并将顶点着色器和片段着色器绑定到它上面：

private int program;
...
// initialize shader program
int vertexShader = GLES20.glCreateShader(GLES20.GL_VERTEX_SHADER);
GLES20.glShaderSource(vertexShader, VERTEX_SHADER);
GLES20.glCompileShader(vertexShader);
int fragmentShader = GLES20.glCreateShader(GLES20.GL_FRAGMENT_SHADER);
GLES20.glShaderSource(fragmentShader, FRAGMENT_SHADER);
GLES20.glCompileShader(fragmentShader);
program = GLES20.glCreateProgram();
GLES20.glAttachShader(program, vertexShader);
GLES20.glAttachShader(program, fragmentShader);
GLES20.glLinkProgram(program);

7. 最后，我们需要在渲染循环中将顶点坐标和纹理坐标传递给着色器程序，并绘制正方形：

// set up MVP matrix
Matrix.setIdentityM(mvpMatrix, 0);
Matrix.multiplyMM(mvpMatrix, 0, projectionMatrix, 0, viewMatrix, 0);
Matrix.multiplyMM(mvpMatrix, 0, modelMatrix, 0, mvpMatrix, 0);
GLES20.glUniformMatrix4fv(mvpMatrixHandle, 1, false, mvpMatrix, 0);

// set up vertex attributes
int positionHandle = GLES20.glGetAttribLocation(program, "aPosition");
GLES20.glEnableVertexAttribArray(positionHandle);
GLES20.glVertexAttribPointer(positionHandle, 3, GLES20.GL_FLOAT, false, 0, vertexBuffer);
int textureCoordHandle = GLES20.glGetAttribLocation(program, "aTextureCoord");
GLES20.glEnableVertexAttribArray(textureCoordHandle);
GLES20.glVertexAttribPointer(textureCoordHandle, 2, GLES20.GL_FLOAT, false, 0, vertexBuffer);

// bind texture
GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textures[0]);
GLES20.glUniform1i(textureSamplerHandle, 0);

// draw
GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);

// clean up
GLES20.glDisableVertexAttribArray(positionHandle);
GLES20.glDisableVertexAttribArray(textureCoordHandle);

完整的例子代码可以在下面找到：

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.opengl.GLES20;
import android.opengl.GLUtils;
import android.opengl.Matrix;

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

public class TextureRenderer {

    private static final String VERTEX_SHADER =
            "uniform mat4 uMVPMatrix;\n" +
            "attribute vec4 aPosition;\n" +
            "attribute vec2 aTextureCoord;\n" +
            "varying vec2 vTextureCoord;\n" +
            "void main() {\n" +
            "  gl_Position = uMVPMatrix * aPosition;\n" +
            "  vTextureCoord = aTextureCoord;\n" +
            "}\n";

    private static final String FRAGMENT_SHADER =
            "precision mediump float;\n" +
            "varying vec2 vTextureCoord;\n" +
            "uniform sampler2D uTextureSampler;\n" +
            "void main() {\n" +
            "  gl_FragColor = texture2D(uTextureSampler, vTextureCoord);\n" +
            "}\n";

    private static final float[] VERTEX_ARRAY = {
            // Vertex coordinates (x,y,z)
            -1f,  1f, 0f, // top left
             1f,  1f, 0f, // top right
            -1f, -1f, 0f, // bottom left
             1f, -1f, 0f, // bottom right

            // Texture coordinates (u,v)
            0f, 1f, // top left
            1f, 1f, // top right
            0f, 0f, // bottom left
            1f, 0f  // bottom right
    };

    private FloatBuffer vertexBuffer;
    private int[] textures = new int[1];
    private int program;
    private int mvpMatrixHandle;
    private int textureSamplerHandle;
    private float[] modelMatrix = new float[16];
    private float[] viewMatrix = new float[16];
    private float[] projectionMatrix = new float[16];
    private float[] mvpMatrix = new float[16];

    public TextureRenderer(Context context) {
        // initialize vertex buffer
        ByteBuffer bb = ByteBuffer.allocateDirect(VERTEX_ARRAY.length * 4);
        bb.order(ByteOrder.nativeOrder());
        vertexBuffer = bb.asFloatBuffer();
        vertexBuffer.put(VERTEX_ARRAY);
        vertexBuffer.position(0);

        // load texture
        Bitmap textureBitmap = BitmapFactory.decodeResource(context.getResources(), R.drawable.texture);
        GLES20.glGenTextures(1, textures, 0);
        GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textures[0]);
        GLUtils.texImage2D(GLES20.GL_TEXTURE_2D, 0, textureBitmap, 0);
        textureBitmap.recycle();

        // initialize shader program
        int vertexShader = GLES20.glCreateShader(GLES20.GL_VERTEX_SHADER);
        GLES20.glShaderSource(vertexShader, VERTEX_SHADER);
        GLES20.glCompileShader(vertexShader);
        int fragmentShader = GLES20.glCreateShader(GLES20.GL_FRAGMENT_SHADER);
        GLES20.glShaderSource(fragmentShader, FRAGMENT_SHADER);
        GLES20.glCompileShader(fragmentShader);
        program = GLES20.glCreateProgram();
        GLES20.glAttachShader(program, vertexShader);
        GLES20.glAttachShader(program, fragmentShader);
        GLES20.glLinkProgram(program);

        // get attribute and uniform handles
        mvpMatrixHandle = GLES20.glGetUniformLocation(program, "uMVPMatrix");
        textureSamplerHandle = GLES20.glGetUniformLocation(program, "uTextureSampler");

        // set up matrices
        Matrix.setIdentityM(modelMatrix, 0);
        Matrix.setLookAtM(viewMatrix, 0, 0, 0, -5, 0, 0, 0, 0, 1, 0);
        Matrix.orthoM(projectionMatrix, 0, -1, 1, -1, 1, 3, 7);
    }

    public void draw() {
        // set up MVP matrix
        Matrix.setIdentityM(mvpMatrix, 0);
        Matrix.multiplyMM(mvpMatrix, 0, projectionMatrix, 0, viewMatrix, 0);
        Matrix.multiplyMM(mvpMatrix, 0, modelMatrix, 0, mvpMatrix, 0);
        GLES20.glUniformMatrix4fv(mvpMatrixHandle, 1, false, mvpMatrix, 0);

        // set up vertex attributes
        int positionHandle = GLES20.glGetAttribLocation(program, "aPosition");
        GLES20.glEnableVertexAttribArray(positionHandle);
        GLES20.glVertexAttribPointer(positionHandle, 3, GLES20.GL_FLOAT, false, 0, vertexBuffer);
        int textureCoordHandle = GLES20.glGetAttribLocation(program, "aTextureCoord");
        GLES20.glEnableVertexAttribArray(textureCoordHandle);
        GLES20.glVertexAttribPointer(textureCoordHandle, 2, GLES20.GL_FLOAT, false, 0, vertexBuffer);

        // bind texture
        GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
        GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textures[0]);
        GLES20.glUniform1i(textureSamplerHandle, 0);

        // draw
        GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);

        // clean up
        GLES20.glDisableVertexAttribArray(positionHandle);
        GLES20.glDisableVertexAttribArray(textureCoordHandle);
    }

}