【OpenGL ES】纹理贴图

1 前言

        纹理贴图是指：将图片贴在模型的表面。

        纹理贴图的本质是：将图片划分为一系列三角形，使得图片顶点序列与模型顶点序列中的顶点一一对应，对于模型中任意三角形内部的坐标和图片中对应三角形内部的坐标，可以通过插值，建立一一对应关系，模型中任意位置的颜色由其对应的图片位置的颜色填充。

        本文完整代码资源见→【OpenGL ES】纹理贴图

        项目目录如下：

2 案例

        MainActivity.java

package com.zhyan8.texture;

import android.opengl.GLSurfaceView;
import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {
    private GLSurfaceView mGlSurfaceView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mGlSurfaceView = new MyGLSurfaceView(this);
        setContentView(mGlSurfaceView);
        mGlSurfaceView.setRenderer(new MyRender(this));
    }

    @Override
    protected void onResume() {
        super.onResume();
        mGlSurfaceView.onResume();
    }

    @Override
    protected void onPause() {
        super.onPause();
        mGlSurfaceView.onPause();
    }
}

        MyGLSurfaceView.java

package com.zhyan8.texture;

import android.content.Context;
import android.opengl.GLSurfaceView;
import android.util.AttributeSet;

public class MyGLSurfaceView extends GLSurfaceView {
    public MyGLSurfaceView(Context context) {
        super(context);
        setEGLContextClientVersion(3);
    }

    public MyGLSurfaceView(Context context, AttributeSet attrs) {
        super(context, attrs);
        setEGLContextClientVersion(3);
    }
}

        MyRender.java

package com.zhyan8.texture;

import android.content.Context;
import android.opengl.GLES30;
import android.opengl.GLSurfaceView;
import java.nio.FloatBuffer;
import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;

public class MyRender implements GLSurfaceView.Renderer {
    private FloatBuffer vertexBuffer;
    private FloatBuffer textureBuffer;
    private MyGLUtils mGLUtils;
    private float[] mvpMatrix = new float[16];
    private int mvpMatrixLocation;
    private int mTextureId;

    public MyRender(Context context) {
        mGLUtils = new MyGLUtils(context);
        getFloatBuffer();
    }

    @Override
    public void onSurfaceCreated(GL10 gl, EGLConfig eglConfig) {
        //设置背景颜色
        GLES30.glClearColor(0.1f, 0.2f, 0.3f, 0.4f);
        //编译着色器
        final int vertexShaderId = mGLUtils.compileShader(GLES30.GL_VERTEX_SHADER, R.raw.vertex_shader);
        final int fragmentShaderId = mGLUtils.compileShader(GLES30.GL_FRAGMENT_SHADER, R.raw.fragment_shader);
        //链接程序片段
        int programId = mGLUtils.linkProgram(vertexShaderId, fragmentShaderId);
        GLES30.glUseProgram(programId);
        mvpMatrixLocation = GLES30.glGetUniformLocation(programId, "mvpMatrix");
        mTextureId = mGLUtils.loadTexture(R.raw.xxx);
    }

    @Override
    public void onSurfaceChanged(GL10 gl, int width, int height) {
        //设置视图窗口
        GLES30.glViewport(0, 0, width, height);
        mGLUtils.transform(width, height, mvpMatrix);
    }

    @Override
    public void onDrawFrame(GL10 gl) {
        //将颜色缓冲区设置为预设的颜色
        GLES30.glClear(GLES30.GL_COLOR_BUFFER_BIT);
        GLES30.glUniformMatrix4fv(mvpMatrixLocation, 1, false, mvpMatrix, 0);
        //启用顶点的数组句柄
        GLES30.glEnableVertexAttribArray(0);
        GLES30.glEnableVertexAttribArray(1);
        //准备顶点坐标和纹理坐标
        GLES30.glVertexAttribPointer(0, 3, GLES30.GL_FLOAT, false, 0, vertexBuffer);
        GLES30.glVertexAttribPointer(1, 2, GLES30.GL_FLOAT, false, 0, textureBuffer);
        //激活纹理
        GLES30.glActiveTexture(GLES30.GL_TEXTURE);
        //绑定纹理
        GLES30.glBindTexture(GLES30.GL_TEXTURE_2D, mTextureId);
        //绘制贴图
        GLES30.glDrawArrays(GLES30.GL_TRIANGLE_FAN, 0, 4);
        //禁止顶点数组句柄
        GLES30.glDisableVertexAttribArray(0);
        GLES30.glDisableVertexAttribArray(1);
    }

    private void getFloatBuffer() {
        float[] vertex = new float[] {
                1f, 1f, 0f,     //V0
                -1f, 1f, 0f,    //V1
                -1f, -1f, 0f,   //V2
                1f, -1f, 0f     //V3
        };
        float[] texture = {
                1f, 0f,     //V0
                0f, 0f,     //V1
                0f, 1.0f,   //V2
                1f, 1.0f    //V3
        };
        vertexBuffer = mGLUtils.getFloatBuffer(vertex);
        textureBuffer = mGLUtils.getFloatBuffer(texture);
    }
}

        MyGLUtils.java

package com.zhyan8.texture;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.opengl.GLES30;
import android.opengl.GLUtils;
import android.opengl.Matrix;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;

public class MyGLUtils {
    private Context mContext;
    private Bitmap mBitmap;

    public MyGLUtils(Context context) {
        mContext = context;
    }

    public FloatBuffer getFloatBuffer(float[] floatArr) {
        FloatBuffer fb = ByteBuffer.allocateDirect(floatArr.length * Float.BYTES)
            .order(ByteOrder.nativeOrder())
            .asFloatBuffer();
        fb.put(floatArr);
        fb.position(0);
        return fb;
    }

    //通过代码片段编译着色器
    public int compileShader(int type, String shaderCode){
        int shader = GLES30.glCreateShader(type);
        GLES30.glShaderSource(shader, shaderCode);
        GLES30.glCompileShader(shader);
        return shader;
    }

    //通过外部资源编译着色器
    public int compileShader(int type, int shaderId){
        String shaderCode = readShaderFromResource(shaderId);
        return compileShader(type, shaderCode);
    }

    //链接到着色器
    public int linkProgram(int vertexShaderId, int fragmentShaderId) {
        final int programId = GLES30.glCreateProgram();
        //将顶点着色器加入到程序
        GLES30.glAttachShader(programId, vertexShaderId);
        //将片元着色器加入到程序
        GLES30.glAttachShader(programId, fragmentShaderId);
        //链接着色器程序
        GLES30.glLinkProgram(programId);
        return programId;
    }

    //从shader文件读出字符串
    private String readShaderFromResource(int shaderId) {
        InputStream is = mContext.getResources().openRawResource(shaderId);
        BufferedReader br = new BufferedReader(new InputStreamReader(is));
        String line;
        StringBuilder sb = new StringBuilder();
        try {
            while ((line = br.readLine()) != null) {
                sb.append(line);
                sb.append("\n");
            }
            br.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return sb.toString();
    }

    //加载纹理贴图
    public int loadTexture(int resourceId) {
        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inScaled = false;
        mBitmap = BitmapFactory.decodeResource(mContext.getResources(), resourceId, options);
        final int[] textureIds = new int[1];
        // 生成纹理id
        GLES30.glGenTextures(1, textureIds, 0);
        // 绑定纹理到OpenGL
        GLES30.glBindTexture(GLES30.GL_TEXTURE_2D, textureIds[0]);
        GLES30.glTexParameteri(GLES30.GL_TEXTURE_2D, GLES30.GL_TEXTURE_MIN_FILTER, GLES30.GL_LINEAR_MIPMAP_LINEAR);
        GLES30.glTexParameteri(GLES30.GL_TEXTURE_2D, GLES30.GL_TEXTURE_MAG_FILTER, GLES30.GL_LINEAR);
        // 加载bitmap到纹理中
        GLUtils.texImage2D(GLES30.GL_TEXTURE_2D, 0, mBitmap, 0);
        // 生成MIP贴图
        GLES30.glGenerateMipmap(GLES30.GL_TEXTURE_2D);
        // 取消绑定纹理
        GLES30.glBindTexture(GLES30.GL_TEXTURE_2D, 0);
        return textureIds[0];
    }

    //调整图片宽高适配屏幕尺寸
    public void transform(int width, int height, float[] matrix) {
        int mapWidth = mBitmap.getWidth();
        int mapHeight = mBitmap.getHeight();
        float mapRatio = mapWidth / (float)mapHeight;
        float ratio = width / (float)height;
        float w = 1.0f;
        float h = 1.0f;
        if (mapRatio > ratio) { //宽度最大，高度适配
            h = mapRatio / ratio;
        } else { //高度最大，宽度适配
            w = ratio / mapRatio;
        }
        Matrix.orthoM(matrix, 0, -w, w, -h, h,-1, 1);
    }
}

        vertex_shader.glsl

#version 300 es
layout (location = 0) in vec4 aPosition;
layout (location = 1) in vec2 aTextureCoord;
uniform mat4 mvpMatrix;
out vec2 vTexCoord;
void main() {
     gl_Position  = mvpMatrix * aPosition;
     vTexCoord = aTextureCoord;
}

//attribute vec4 aPosition;
//attribute vec2 aTextureCoord;
//uniform mat4 mvpMatrix;
//varying vec2 vTexCoord;
//void main() {
//     gl_Position  = mvpMatrix * aPosition;
//     vTexCoord = aTextureCoord;
//}

        顶点着色器的作用：进行矩阵变换位置、根据光照公式计算顶点颜⾊、⽣成 / 变换纹理坐标，并且把位置和纹理坐标发送到片元着色器。 

        顶点着色器中，如果没有指定默认精度，则 int 和 float 的默认精度都为 highp。

        fragment_shader.glsl

#version 300 es
precision mediump float;
uniform sampler2D uTextureUnit;
in vec2 vTexCoord;
out vec4 fragColor;
void main() {
     fragColor = texture(uTextureUnit, vTexCoord);
}

//precision mediump float;
//uniform sampler2D uTextureUnit;
//varying vec2 vTexCoord;
//void main() {
//     gl_FragColor = texture2D(uTextureUnit, vTexCoord);
//}

        片元着色器的作用：处理经光栅化阶段生成的每个片元，计算每个像素的颜色和透明度。 

        在片元着色器中，浮点值没有默认的精度值，每个着色器必须声明一个默认的 float 精度。

        运行结果：