简单的天空盒和天空穹顶

天空盒：

• 使用一个立方体网格，纹理设置为所需环境，将立方体放在相机上。
• 禁用深度测试先渲染天空盒。
• 天空盒随相机移动。

天空穹顶：

• 区别是使用球体或者半球体代替立方体。

CubeMap实现天空盒

优点是可减少接缝以及支持环境贴图。

实现

• 网格创建和缓存区:

  //天空盒网格
    float cubeVertexPositions[108] =
    { -1.0f,  1.0f, -1.0f, -1.0f, -1.0f, -1.0f, 1.0f, -1.0f, -1.0f,
        1.0f, -1.0f, -1.0f, 1.0f,  1.0f, -1.0f, -1.0f,  1.0f, -1.0f,
        1.0f, -1.0f, -1.0f, 1.0f, -1.0f,  1.0f, 1.0f,  1.0f, -1.0f,
        1.0f, -1.0f,  1.0f, 1.0f,  1.0f,  1.0f, 1.0f,  1.0f, -1.0f,
        1.0f, -1.0f,  1.0f, -1.0f, -1.0f,  1.0f, 1.0f,  1.0f,  1.0f,
        -1.0f, -1.0f,  1.0f, -1.0f,  1.0f,  1.0f, 1.0f,  1.0f,  1.0f,
        -1.0f, -1.0f,  1.0f, -1.0f, -1.0f, -1.0f, -1.0f,  1.0f,  1.0f,
        -1.0f, -1.0f, -1.0f, -1.0f,  1.0f, -1.0f, -1.0f,  1.0f,  1.0f,
        -1.0f, -1.0f,  1.0f,  1.0f, -1.0f,  1.0f,  1.0f, -1.0f, -1.0f,
        1.0f, -1.0f, -1.0f, -1.0f, -1.0f, -1.0f, -1.0f, -1.0f,  1.0f,
        -1.0f,  1.0f, -1.0f, 1.0f,  1.0f, -1.0f, 1.0f,  1.0f,  1.0f,
        1.0f,  1.0f,  1.0f, -1.0f,  1.0f,  1.0f, -1.0f,  1.0f, -1.0f
    };
    glGenVertexArrays(1, vao);
    glBindVertexArray(vao[0]);
    glGenBuffers(numVBOs, vbo[99]);
  
    glBindBuffer(GL_ARRAY_BUFFER, vbo[99][0]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(cubeVertexPositions), cubeVertexPositions, GL_STATIC_DRAW);
  

• 渲染：

    //********** 天空盒 *********************************
    glUseProgram(renderingProgramCubemap);
  
    vLoc = glGetUniformLocation(renderingProgramCubemap, "v_matrix");
    glUniformMatrix4fv(vLoc, 1, GL_FALSE, glm::value_ptr(vMat));
  
    projLoc = glGetUniformLocation(renderingProgramCubemap, "p_matrix");
    glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(pMat));
  
    glBindBuffer(GL_ARRAY_BUFFER, vbo[99][0]);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
    glEnableVertexAttribArray(0);
  
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_CUBE_MAP, texSkybox);
  
    glEnable(GL_CULL_FACE);
    glFrontFace(GL_CCW);	// cube is CW, but we are viewing the inside
    glDisable(GL_DEPTH_TEST);
    glDrawArrays(GL_TRIANGLES, 0, 36);
    glEnable(GL_DEPTH_TEST);
    //****************************************************
  

• 着色器： ```GLSL //vert shader: #version 430

layout (location = 0) in vec3 position; out vec3 cubetc;

uniform mat4 v_matrix; uniform mat4 p_matrix; layout (binding = 0) uniform samplerCube samp;

void main(void) { cubetc = position;//纹理坐标就是顶点坐标 mat4 v3_matrix = mat4(mat3(v_matrix));//去除V矩阵中的平移 gl_Position = p_matrix * v3_matrix * vec4(position,1.0); }

//frag shader: #version 430

in vec3 cubetc; out vec4 fragColor;

uniform mat4 v_matrix; uniform mat4 p_matrix; layout (binding = 0) uniform samplerCube samp;

void main(void) { fragColor = texture(samp,cubetc); }

<br />

# CubeMap实现环境贴图  

程序：
```CPP
//...
//激活环境纹理
glActiveTexture(GL_TEXTURE???);			//纹理单元1-绑定环境纹理
glBindTexture(GL_TEXTURE_CUBE_MAP, texSkybox);
//激活其他纹理...
//绘制...

着色器：

//片段着色器的部分代码
//...
layout(binding = 1) uniform samplerCube envTex;
//...

void main(void)
{
	vec3 Nview = normalize(varyingNormal);
	vec3 Lview = normalize((v_matrix * vec4(-light.dir, 0.0)).xyz);
	vec3 Vview = normalize(-varyingPos);
	vec3 Hview = normalize(Lview + Vview);
	vec3 Rview = reflect(normalize(varyingPos), normalize(varyingNormal));

	vec3 Rworld = (vec4(Rview, 0.0) * v_matrix).xyz;

	vec4 env_color = texture(envTex,Rworld);
    //...
    //(可以视光滑/粗糙度进行滤波模糊)
}