【OpenGL ES】立方体贴图（6张图）

1 前言

​ 本文通过一个立方体贴图的例子，讲解三维纹理贴图的应用，案例中使用 6 张不同的图片给立方体贴图，图片如下：

​ 本文涉及到的知识点主要包含：三维绘图、MVP 矩阵变换、纹理贴图，读者如果对 OpenGL ES 不太熟悉，请回顾以下内容：

• 绘制三角形
• 绘制立方体
• MVP矩阵变换
• 纹理贴图

​ 本文完整代码资源见→ 【OpenGL ES】立方体贴图（6张图）

​ 项目目录如下：

2 案例

​ MainActivity.java

package com.zhyan8.texture3d;

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.texture3d;

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.texture3d;

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 int mProgramId;
    private float mRatio;
    private int[] mTextureIds;

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

    @Override
    public void onSurfaceCreated(GL10 gl, EGLConfig eglConfig) {
        //设置背景颜色
        GLES30.glClearColor(0.1f, 0.2f, 0.3f, 0.4f);
        //启动深度测试
        gl.glEnable(GLES30.GL_DEPTH_TEST);
        //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
        mProgramId = mGLUtils.linkProgram(vertexShaderId, fragmentShaderId);
        GLES30.glUseProgram(mProgramId);
        mTextureIds = mGLUtils.loadTexture(Model.resIds);
    }

    @Override
    public void onSurfaceChanged(GL10 gl, int width, int height) {
        //设置视图窗口
        GLES30.glViewport(0, 0, width, height);
        getFloatBuffer();
        mRatio = 1.0f * width / height;
    }

    @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.GL_DEPTH_BUFFER_BIT);
        mGLUtils.transform(mProgramId, mRatio); //计算MVP变换矩阵
        //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);
        //绘制纹理
        drawTextures();
        //禁止顶点数组句柄
        GLES30.glDisableVertexAttribArray(0);
        GLES30.glDisableVertexAttribArray(1);
    }

    private void getFloatBuffer() {
        vertexBuffer = mGLUtils.getFloatBuffer(Model.vertex);
        textureBuffer = mGLUtils.getFloatBuffer(Model.texture);
    }

    private void drawTextures() {
        int count = 4;
        for (int i =0; i < mTextureIds.length; i++) {
            int first = i * count;
            //绑定纹理
            GLES30.glBindTexture(GLES30.GL_TEXTURE_2D, mTextureIds[i]);
            //绘制正方体的表面（6个面，每个面2个三角形）
            GLES30.glDrawArrays(GLES30.GL_TRIANGLE_FAN, first, count);
        }
    }
}

​ GLUtils.java

package com.zhyan8.texture3d;

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 int mRotateAgree = 0;

    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[] resIds) {
        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inScaled = false;
        Bitmap[] bitmaps = new Bitmap[resIds.length];
        // 生成纹理id
        final int[] textureIds = new int[resIds.length];
        GLES30.glGenTextures(resIds.length, textureIds, 0);
        for (int i = 0; i < resIds.length; i++) {
            bitmaps[i] = BitmapFactory.decodeResource(mContext.getResources(), resIds[i], options);
            // 绑定纹理到OpenGL
            GLES30.glBindTexture(GLES30.GL_TEXTURE_2D, textureIds[i]);
            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, bitmaps[i], 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);
            bitmaps[i].recycle();
        }
        return textureIds;
    }

    //计算MVP变换矩阵
    public void transform(int programId, float ratio) {
        //初始化modelMatrix, viewMatrix, projectionMatrix
        float[] modelMatrix = getIdentityMatrix(16, 0); //模型变换矩阵
        float[] viewMatrix = getIdentityMatrix(16, 0); //观测变换矩阵
        float[] projectionMatrix = getIdentityMatrix(16, 0); //投影变换矩阵
        //获取modelMatrix, viewMatrix, projectionMatrix
        mRotateAgree = (mRotateAgree + 2) % 360;
        Matrix.rotateM(modelMatrix, 0, mRotateAgree, -1, -1, 1); //获取模型旋转变换矩阵
        Matrix.setLookAtM(viewMatrix, 0, 0, 5, 10, 0, 0, 0, 0, 1, 0); //获取观测变换矩阵
        Matrix.frustumM(projectionMatrix, 0, -ratio, ratio, -1, 1, 3, 20); //获取投影变换矩阵
        //计算MVP变换矩阵: mvpMatrix = projectionMatrix * viewMatrix * modelMatrix
        float[] tempMatrix = new float[16];
        float[] mvpMatrix = new float[16];
        Matrix.multiplyMM(tempMatrix, 0, viewMatrix, 0, modelMatrix, 0);
        Matrix.multiplyMM(mvpMatrix, 0, projectionMatrix, 0, tempMatrix, 0);
        //设置MVP变换矩阵
        int mvpMatrixHandle = GLES30.glGetUniformLocation(programId, "mvpMatrix");
        GLES30.glUniformMatrix4fv(mvpMatrixHandle, 1, false, mvpMatrix, 0);
    }

    private float[] getIdentityMatrix(int size, int offset) {
        float[] matrix = new float[size];
        Matrix.setIdentityM(matrix, offset);
        return matrix;
    }
}

​ Model.java

package com.zhyan8.texture3d;

public class Model {
    private static float r = 1.0f;

    public static int[] resIds = new int[] {
            R.raw.x1, R.raw.x2, R.raw.x3,
            R.raw.x4, R.raw.x5, R.raw.x6
    };

    public static float[] vertex = new float[] {
            //前面
            r, r, r,
            -r, r, r,
            -r, -r, r,
            r, -r, r,
            //后面
            r, r, -r,
            -r, r, -r,
            -r, -r, -r,
            r, -r, -r,
            //上面
            r, r, r,
            r, r, -r,
            -r, r, -r,
            -r, r, r,
            //下面
            r, -r, r,
            r, -r, -r,
            -r, -r, -r,
            -r, -r, r,
            //右面
            r, r, r,
            r, r, -r,
            r, -r, -r,
            r, -r, r,
            //左面
            -r, r, r,
            -r, r, -r,
            -r, -r, -r,
            -r, -r, r
    };

    public static float[] texture = new float[] {
            //前面
            0f, 0f,
            1f, 0f,
            1f, 1f,
            0f, 1f,
            //后面
            0f, 0f,
            1f, 0f,
            1f, 1f,
            0f, 1f,
            //上面
            0f, 0f,
            1f, 0f,
            1f, 1f,
            0f, 1f,
            //下面
            0f, 0f,
            1f, 0f,
            1f, 1f,
            0f, 1f,
            //右面
            0f, 0f,
            1f, 0f,
            1f, 1f,
            0f, 1f,
            //左面
            0f, 0f,
            1f, 0f,
            1f, 1f,
            0f, 1f
    };
}

​ vertex_shader.glsl

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

​ 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。

​ 运行效果：

​ 声明：本文转自【OpenGL ES】立方体贴图（6张图）