十六、立方体贴图（天空盒）

第一部分 概念：

1) 引用

OpenGL ES 立方体贴图本质上还是纹理映射，是一种 3D 纹理映射。立方体贴图所使的纹理称为立方图纹理，它是由 6 个单独的 2D 纹理组成，每个 2D 纹理是立方图的一个面。

立方图纹理的采样通过一个 3D 向量（s, t, r）作为纹理坐标，这个 3D 向量只作为方向向量使用，OpenGL ES 获取方向向量触碰到立方图表面上的纹理像素作为采样结果。方向向量触碰到立方图表面对应的纹理位置作为采样点，要求立方图的中心必须位于原点。

立方图各个面的指定方法与 2D 纹理基本相同，且每个面必须为正方形（宽度和高度必须相同）。

2）应用

3D纹理跟2D纹理差不多，都是要先生成一个纹理，再绑定，只是2D的是绑定到GL_TEXTURE_2D，而3D的是绑定到**GL_TEXTURE_CUBE_MAP**

GLuint textureID;
glGenTextures(1, &textureID);
glBindTexture(GL_TEXTURE_CUBE_MAP, textureID);

由于立方图包含 6 个纹理，每个面对应一个纹理，需要调用glTexImage2D函数 6 次，OpenGL ES 为立方图提供了 6 个不同的纹理目标，对应立方图的 6 个面，且 6 个纹理目标按顺序依次增 1。

glGenTextures(1, &m_TextureId);
glBindTexture(GL_TEXTURE_CUBE_MAP, m_TextureId);
for (int i = 0; i < m_vcImage.size(); ++i)
{
//6个面的纹理是挨个+1glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, 0,GL_RGBA, m_vcImage[i].width, m_vcImage[i].height, 0, GL_RGBA, GL_UNSIGNED_BYTE,m_vcImage[i].data);LOGD("glTexImage2D %d",i);
}
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);
glBindTexture(GL_TEXTURE_CUBE_MAP, 0);

片段着色器也需要修改，采样器变成了 samplerCube，并且纹理坐标变成了三维方向向量。

#version 300 es
precision mediump float;
in vec3 v_texCoord;
layout(location = 0) out vec4 outColor;
uniform samplerCube s_SkyBox;
void main()
{outColor = texture(s_SkyBox, v_texCoord);
}

第二部分 实践

天空盒内绘制一个立方体，并让立方体的表面反射它周围环境的属性

天空之盒的顶点着色器vSkyBox.vs

#version 300 es
precision mediump float;
layout(location = 0) in vec3 a_position;
uniform mat4 u_MVPMatrix;
out vec3 v_texCoord;
void main()
{gl_Position = u_MVPMatrix * vec4(a_position, 1.0);v_texCoord = a_position;
}

天空之盒的片段着色器fSkyBox.fs

#version 300 es
precision mediump float;
in vec3 v_texCoord;
layout(location = 0) out vec4 outColor;
uniform samplerCube s_SkyBox;//3D纹理为samplerCube类型
void main()
{outColor = texture(s_SkyBox, v_texCoord);
}

立方体的顶点着色器vCube.vs

#version 300 es
precision mediump float;
layout(location = 0) in vec3 a_position;
layout(location = 1) in vec3 a_normal;
uniform mat4 u_MVPMatrix;
uniform mat4 u_ModelMatrix;
out vec3 v_texCoord;
out vec3 v_normal;
void main()
{gl_Position = u_MVPMatrix * vec4(a_position, 1.0);v_normal = mat3(transpose(inverse(u_ModelMatrix))) * a_normal;v_texCoord = vec3(u_ModelMatrix * vec4(a_position, 1.0));
}

立方体的片段着色器fCube.fs

#version 300 es
precision mediump float;
in vec3 v_texCoord;
in vec3 v_normal;
layout(location = 0) out vec4 outColor;
uniform samplerCube s_SkyBox;
uniform vec3 u_cameraPos;
void main()
{float ratio = 1.00 / 1.52;vec3 I = normalize(v_texCoord - u_cameraPos);//反射vec3 R = reflect(I, normalize(v_normal));//折射//vec3 R = refract(I, normalize(v_normal), ratio);outColor = texture(s_SkyBox, R);
}

Skybox.h文件

//
// Created by CreatWall_zhouwen on 2023/5/23.
//#ifndef ELEVENSKYBOX_SKYBOX_H
#define ELEVENSKYBOX_SKYBOX_H
#include <GLES3/gl3.h>
#include <detail/type_mat.hpp>
#include <detail/type_mat4x4.hpp>
#include <vector>
#include <map>
#include "Const.h"
#define MATH_PI 3.1415926535897932384626433832802
class Skybox {
public:Skybox(){m_SamplerLoc = GL_NONE;m_MVPMatLoc = GL_NONE;m_TextureId = GL_NONE;m_SkyBoxVaoId = GL_NONE;m_AngleX = 0;m_AngleY = 0;m_ScaleX = 1.0f;m_ScaleY = 1.0f;m_ModelMatrix = glm::mat4(0.0f);};~Skybox(){};void CreateProgram(const char *ver, const char *frag,const char *curver, const char *curfrag);void Draw();static Skybox* GetInstance();static void DestroyInstance();void OnSurfaceChanged(int width, int height);void UpdateTransformMatrix(float rotateX, float rotateY, float scaleX, float scaleY);void UpdateMVPMatrix(glm::mat4 &mvpMatrix, int angleX, int angleY, float scale, float ratio);void getTexturedata(std::vector<struct ImageTyep> vcImagetemp);
private:GLuint m_TextureId;//纹理IDGLuint m_CubeProgramObj;//立方体工程GLuint m_ProgramObj;//天空盒工程GLuint m_VertexShader;GLuint m_FragmentShader;GLint m_SamplerLoc;//天空盒着色器中uinform变量GLint m_MVPMatLoc;GLint m_CubeSamplerLoc;//立方体着色器中uinform变量GLint m_CubeMVPMatLoc;GLint m_CubeModelMatLoc;GLint m_ViewPosLoc;GLuint m_CubeVaoId;GLuint m_CubeVboId;GLuint m_SkyBoxVaoId;GLuint m_SkyBoxVboId;std::vector<struct ImageTyep> m_vcImage;//存放纹理数据int srceenWidth, srceenHeight;//屏幕宽高glm::mat4 m_MVPMatrix;glm::mat4 m_ModelMatrix;int m_AngleX;int m_AngleY;float m_ScaleX;float m_ScaleY;
};#endif //ELEVENSKYBOX_SKYBOX_H

Skybox.cpp文件

//
// Created by CreatWall_zhouwen on 2023/5/23.
//#include "Skybox.h"
#include "Util.h"
#include "GLUtil.h"
#include <gtc/matrix_transform.hpp>
Skybox* m_pContext = nullptr;
#define TAG "DRAWTEXTURE"
GLfloat cubeVertices[] = {//position           //normal-0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,-0.5f,  0.5f, -0.5f,  0.0f,  0.0f, -1.0f,-0.5f, -0.5f, -0.5f,  0.0f,  0.0f, -1.0f,-0.5f, -0.5f, 0.5f,   0.0f,  0.0f,  1.0f,0.5f, -0.5f, 0.5f,   0.0f,  0.0f,  1.0f,0.5f,  0.5f, 0.5f,   0.0f,  0.0f,  1.0f,0.5f,  0.5f, 0.5f,   0.0f,  0.0f,  1.0f,-0.5f,  0.5f, 0.5f,   0.0f,  0.0f,  1.0f,-0.5f, -0.5f, 0.5f,   0.0f,  0.0f,  1.0f,-0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,-0.5f,  0.5f, -0.5f,  1.0f,  0.0f,  0.0f,-0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,-0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,-0.5f, -0.5f,  0.5f,  1.0f,  0.0f,  0.0f,-0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,0.5f,  0.5f, -0.5f,  1.0f,  0.0f,  0.0f,0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,0.5f, -0.5f, -0.5f,  1.0f,  0.0f,  0.0f,0.5f, -0.5f,  0.5f,  1.0f,  0.0f,  0.0f,0.5f,  0.5f,  0.5f,  1.0f,  0.0f,  0.0f,-0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,-0.5f, -0.5f,  0.5f,  0.0f, -1.0f,  0.0f,-0.5f, -0.5f, -0.5f,  0.0f, -1.0f,  0.0f,-0.5f, 0.5f, -0.5f,   0.0f,  1.0f,  0.0f,0.5f, 0.5f, -0.5f,   0.0f,  1.0f,  0.0f,0.5f, 0.5f,  0.5f,   0.0f,  1.0f,  0.0f,0.5f, 0.5f,  0.5f,   0.0f,  1.0f,  0.0f,-0.5f, 0.5f,  0.5f,   0.0f,  1.0f,  0.0f,-0.5f, 0.5f, -0.5f,   0.0f,  1.0f,  0.0f,
};GLfloat skyboxVertices[] = {// Positions-2.0f,  2.0f, -2.0f,-2.0f, -2.0f, -2.0f,2.0f, -2.0f, -2.0f,2.0f, -2.0f, -2.0f,2.0f,  2.0f, -2.0f,-2.0f,  2.0f, -2.0f,-2.0f, -2.0f,  2.0f,-2.0f, -2.0f, -2.0f,-2.0f,  2.0f, -2.0f,-2.0f,  2.0f, -2.0f,-2.0f,  2.0f,  2.0f,-2.0f, -2.0f,  2.0f,2.0f, -2.0f, -2.0f,2.0f, -2.0f,  2.0f,2.0f,  2.0f,  2.0f,2.0f,  2.0f,  2.0f,2.0f,  2.0f, -2.0f,2.0f, -2.0f, -2.0f,-2.0f, -2.0f,  2.0f,-2.0f,  2.0f,  2.0f,2.0f,  2.0f,  2.0f,2.0f,  2.0f,  2.0f,2.0f, -2.0f,  2.0f,-2.0f, -2.0f,  2.0f,-2.0f,  2.0f, -2.0f,2.0f,  2.0f, -2.0f,2.0f,  2.0f,  2.0f,2.0f,  2.0f,  2.0f,-2.0f,  2.0f,  2.0f,-2.0f,  2.0f, -2.0f,-2.0f, -2.0f, -2.0f,-2.0f, -2.0f,  2.0f,2.0f, -2.0f, -2.0f,2.0f, -2.0f, -2.0f,-2.0f, -2.0f,  2.0f,2.0f, -2.0f,  2.0f
};void Skybox::CreateProgram(const char *ver, const char *frag,const char *curver, const char *curfrag) {LOGD("CreateProgram Enter");m_ProgramObj = CreateGLProgram(ver, frag, m_VertexShader, m_FragmentShader);if (m_ProgramObj){m_SamplerLoc = glGetUniformLocation(m_ProgramObj, "s_SkyBox");m_MVPMatLoc = glGetUniformLocation(m_ProgramObj, "u_MVPMatrix");}else{LOGD("SkyBoxSample::Init create m_ProgramObj fail");return;}m_CubeProgramObj = CreateGLProgram(curver, curfrag, m_VertexShader, m_FragmentShader);if (m_CubeProgramObj){m_CubeSamplerLoc = glGetUniformLocation(m_CubeProgramObj, "s_SkyBox");m_CubeMVPMatLoc = glGetUniformLocation(m_CubeProgramObj, "u_MVPMatrix");m_CubeModelMatLoc = glGetUniformLocation(m_CubeProgramObj, "u_ModelMatrix");m_ViewPosLoc = glGetUniformLocation(m_CubeProgramObj, "u_cameraPos");}else{LOGD("SkyBoxSample::Init create m_CubeProgramObj fail");return;}LOGD("CreateProgram Leave");//创建天空盒的VBO 以及绑定VAOglGenBuffers(1, &m_SkyBoxVboId);glBindBuffer(GL_ARRAY_BUFFER, m_SkyBoxVboId);glBufferData(GL_ARRAY_BUFFER, sizeof(skyboxVertices), skyboxVertices, GL_STATIC_DRAW);glGenVertexArrays(1, &m_SkyBoxVaoId);//创建VAOglBindVertexArray(m_SkyBoxVaoId);glBindBuffer(GL_ARRAY_BUFFER, m_SkyBoxVboId);//绑定VBOglEnableVertexAttribArray(0);//绑定VBO数据glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (const void *) 0);glBindBuffer(GL_ARRAY_BUFFER, GL_NONE);glBindVertexArray(GL_NONE);//创建立方体的VBO 以及绑定VAOglGenBuffers(1, &m_CubeVboId);glBindBuffer(GL_ARRAY_BUFFER, m_CubeVboId);glBufferData(GL_ARRAY_BUFFER, sizeof(cubeVertices), cubeVertices, GL_STATIC_DRAW);glGenVertexArrays(1, &m_CubeVaoId);//创建VAOglBindVertexArray(m_CubeVaoId);glBindBuffer(GL_ARRAY_BUFFER, m_CubeVboId);//绑定VBOglEnableVertexAttribArray(0);//属性O的数据glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (const void *) 0);glEnableVertexAttribArray(1);//属性1的数据 对应顶点着色器的location 1glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));glBindBuffer(GL_ARRAY_BUFFER, GL_NONE);glBindVertexArray(GL_NONE);
}void Skybox::Draw() {glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);glClearColor(0.2f, 0.9f, 0.3f, 1.0f);glEnable(GL_DEPTH_TEST);UpdateMVPMatrix(m_MVPMatrix, m_AngleX, m_AngleY, 1.0, (float) srceenWidth / srceenHeight);if (!m_TextureId){//create RGBA textureglGenTextures(1, &m_TextureId);glBindTexture(GL_TEXTURE_CUBE_MAP, m_TextureId);//绑定立体纹理for (int i = 0; i < m_vcImage.size(); ++i){//6个面的纹理是挨个+1glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, 0,GL_RGBA, m_vcImage[i].width, m_vcImage[i].height, 0, GL_RGBA, GL_UNSIGNED_BYTE,m_vcImage[i].data);LOGD("glTexImage2D %d",i);}glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_LINEAR);glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_LINEAR);glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);glBindTexture(GL_TEXTURE_CUBE_MAP, 0);LOGD("sizeof(m_vcImage) / sizeof(ImageTyep) = %d ", sizeof(m_vcImage) / sizeof(ImageTyep));}//画天空盒glUseProgram(m_ProgramObj);glBindVertexArray(m_SkyBoxVaoId);glUniformMatrix4fv(m_MVPMatLoc, 1, GL_FALSE, &m_MVPMatrix[0][0]);glActiveTexture(GL_TEXTURE0);glBindTexture(GL_TEXTURE_CUBE_MAP, m_TextureId);glUniform1i(m_SamplerLoc, 0);glDrawArrays(GL_TRIANGLES, 0, 36);//画立方体UpdateMVPMatrix(m_MVPMatrix, m_AngleX, m_AngleY, 0.4f, (float) srceenWidth / srceenHeight);glUseProgram(m_CubeProgramObj);glBindVertexArray(m_CubeVaoId);glUniformMatrix4fv(m_CubeMVPMatLoc, 1, GL_FALSE, &m_MVPMatrix[0][0]);glUniformMatrix4fv(m_CubeModelMatLoc, 1, GL_FALSE, &m_ModelMatrix[0][0]);glUniform3f(m_ViewPosLoc,  0.0f, 0.0f, 1.8f);glActiveTexture(GL_TEXTURE0);glBindTexture(GL_TEXTURE_CUBE_MAP, m_TextureId);glUniform1i(m_CubeSamplerLoc, 0);glDrawArrays(GL_TRIANGLES, 0, 36);}Skybox *Skybox::GetInstance() {if (m_pContext == nullptr){m_pContext = new Skybox();}return m_pContext;
}void Skybox::DestroyInstance() {if (m_pContext){delete m_pContext;m_pContext = nullptr;}
}void Skybox::OnSurfaceChanged(int width, int height) {glViewport(0, 0, width, height);srceenWidth = width;srceenHeight = height;LOGD("OnSurfaceChanged Srceenwidth = %d, Srceenheight = %d, ratio = %f", width,height);
}void Skybox::UpdateTransformMatrix(float rotateX, float rotateY, float scaleX, float scaleY) {m_AngleX = static_cast<int>(rotateX);m_AngleY = static_cast<int>(rotateY);m_ScaleX = scaleX;m_ScaleY = scaleY;
}void Skybox::UpdateMVPMatrix(glm::mat4 &mvpMatrix, int angleX, int angleY, float scale, float ratio) {LOGD("SkyBoxSample::UpdateMVPMatrix angleX = %d, angleY = %d, ratio = %f", angleX,angleY, ratio);angleX = angleX % 360;angleY = angleY % 360;//转化为弧度角float radiansX = static_cast<float>(MATH_PI / 180.0f * angleX);float radiansY = static_cast<float>(MATH_PI / 180.0f * angleY);// Projection matrix//glm::mat4 Projection = glm::ortho(-ratio, ratio, -1.0f, 1.0f, 0.0f, 100.0f);//glm::mat4 Projection = glm::frustum(-ratio, ratio, -1.0f, 1.0f, 4.0f, 100.0f);glm::mat4 Projection = glm::perspective(45.0f, ratio, 0.1f, 100.f);// View matrixglm::mat4 View = glm::lookAt(glm::vec3(0, 0, 1.8), // Camera is at (0,0,1), in World Spaceglm::vec3(0, 0, -1), // and looks at the originglm::vec3(0, 1, 0)  // Head is up (set to 0,-1,0 to look upside-down));// Model matrixglm::mat4 Model = glm::mat4(1.0f);Model = glm::scale(Model, glm::vec3(scale, scale, scale));Model = glm::rotate(Model, radiansX, glm::vec3(1.0f, 0.0f, 0.0f));Model = glm::rotate(Model, radiansY, glm::vec3(0.0f, 1.0f, 0.0f));Model = glm::translate(Model, glm::vec3(0.0f, 0.0f, 0.0f));m_ModelMatrix = Model;mvpMatrix = Projection * View * Model;
}void Skybox::getTexturedata(std::vector<struct ImageTyep> vcImagetemp) {m_vcImage = vcImagetemp;
}