如何在OpenGL中将纹理设置为背景？

Question

我想制作一个程序，以 space 纹理为背景显示 earth。

• 地球是具有地球纹理 (.bmp) 的 3D 制服。

• 带有星星的空间是一个纹理 (.bmp)。

我已经总结了我要做的事情：

• 创建一个新的模型矩阵
• 将其放置在摄像头所在的同一位置
• 绘图前禁用深度测试
• 反向剔除

这是加载函数：

     void load(){

    //Load The Shader
    Shader simpleShader("src/shader.vert", "src/shader.frag");
    g_simpleShader = simpleShader.program;

    // Create the VAO where we store all geometry (stored in g_Vao)
    g_Vao = gl_createAndBindVAO();

    //Create vertex buffer for positions, colors, and indices, and bind them to shader
    gl_createAndBindAttribute(&(shapes[0].mesh.positions[0]), shapes[0].mesh.positions.size() * sizeof(float), g_simpleShader, "a_vertex", 3);
    gl_createIndexBuffer(&(shapes[0].mesh.indices[0]), shapes[0].mesh.indices.size() * sizeof(unsigned int));
    gl_createAndBindAttribute(uvs, uvs_size, g_simpleShader, "a_uv", 2);
    gl_createAndBindAttribute(normal, normal_size, g_simpleShader, "a_normal", 2);

    //Unbind Everything
    gl_unbindVAO();

    //Store Number of Triangles (use in draw())
    g_NumTriangles = shapes[0].mesh.indices.size() / 3;

    //Paths of the earth and space textures
    Image* image = loadBMP("assets/earthmap1k.bmp");
    Image* space = loadBMP("assets/milkyway.bmp");

    //Generate Textures
    glGenTextures(1, &texture_id);
    glGenTextures(1, &texture_id2);

    //Bind Textures
    glBindTexture(GL_TEXTURE_2D, texture_id);
    glBindTexture(GL_TEXTURE_2D, texture_id2);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

    //We assign your corresponding data
    glTexImage2D(GL_TEXTURE_2D,1,GL_RGB,image->width, image->height,GL_RGB,GL_UNSIGNED_BYTE,image->pixels);
    glTexImage2D(GL_TEXTURE_2D,1,GL_RGB,space->width, space->height,GL_RGB,GL_UNSIGNED_BYTE,space->pixels);

     }

这是绘图函数：

    void draw(){

    //1. Enable/Disable
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glDisable(GL_DEPTH_TEST);   
    glEnable(GL_CULL_FACE);     
    glCullFace(GL_FRONT);   

    //2. Shader Activation
    glUseProgram(g_simpleShader); 

    //3. Get All Uniform Locations

    //Space:
    GLuint model_loc2 = glGetUniformLocation (g_simpleShader, "u_model");
    GLuint u_texture2 = glGetUniformLocation(g_simpleShader, "u_texture2");
    GLuint u_light_dir2 = glGetUniformLocation(g_simpleShader,"u_light_dir2");

    //Earth
    GLuint model_loc = glGetUniformLocation(g_simpleShader, "u_model"); 
    GLuint projection_loc = glGetUniformLocation(g_simpleShader, "u_projection");
    GLuint view_loc = glGetUniformLocation(g_simpleShader, "u_view");
    GLuint u_texture = glGetUniformLocation(g_simpleShader, "u_texture");
    GLuint u_light_dir = glGetUniformLocation(g_simpleShader, "u_light_dir");

    //4. Get Values From All Uniforms
    mat4 model_matrix2 = translate(mat4(1.0f), vec3(1.0f,-3.0f,1.0f));
    mat4 model_matrix = translate(mat4(1.0f),vec3(0.0f,-0.35f,0.0f);
    mat4 projection_matrix = perspective(60.0f,1.0f,0.1f,50.0f);
    mat4 view_matrix = lookAt(vec3( 1.0f, -3.0f,  1.0f),vec3(0.0f, 0.0f, 0.0f), vec3(0.0f, 1.0f, 0.0f)glm::vec3(0,1,0));

     //5. Upload Uniforms To Shader
     glUniformMatrix4fv(model_loc2, 1, GL_FALSE, glm::value_ptr(model_matrix2));

    glUniformMatrix4fv(model_loc, 1, GL_FALSE, glm::value_ptr(model_matrix));
    glUniformMatrix4fv(projection_loc, 1, GL_FALSE, glm::value_ptr(projection_matrix));
    glUniformMatrix4fv(view_loc, 1, GL_FALSE, glm::value_ptr(view_matrix));

    glUniform1i(u_texture, 0);
    glUniform3f(u_light_dir, g_light_dir.x, g_light_dir.y, g_light_dir.z);

    glUniform1i(u_texture2, 1);
    glUniform3f(u_light_dir2, g_light_dir.x, g_light_dir.y, g_light_dir.z);

    //6. Activate Texture Unit 0 and Bind our Texture Object
    glActiveTexture(GL_TEXTURE0);
    glActiveTexture(GL_TEXTURE1);

    glBindTexture(GL_TEXTURE_2D, texture_id);
    glBindTexture(GL_TEXTURE_2D, texture_id2);

    //7. Bind VAO
    gl_bindVAO(g_Vao);

    //8. Draw Elements
    glDrawElements(GL_TRIANGLES, 3 * g_NumTriangles, GL_UNSIGNED_INT, 0);

    }

我还有两个片段着色器：

• 第一个返回这个：

  fragColor = vec4(final_color, 1.0);
  

• 第二个返回这个：

  fragColor = vec4(texture_color.xyz, 1.0);
  

Vertex Shader也返回顶点的位置：

    gl_Position = u_projection * u_view * u_model * vec4( a_vertex , 1.0 );

当我编译时，它只显示地球，而它应该显示地球和空间作为背景。我已经检查了几次代码，但我找不到它是什么。

• 推测结果：

• 我的结果

Answer 1

1. 如果我认为它是正确的，那么你错误地绑定了纹理

   glActiveTexture(GL_TEXTURE0);
   glActiveTexture(GL_TEXTURE1);
   
   glBindTexture(GL_TEXTURE_2D, texture_id);
   glBindTexture(GL_TEXTURE_2D, texture_id2);
   

   应该是：

   glActiveTexture(GL_TEXTURE0);
   glBindTexture(GL_TEXTURE_2D, texture_id);
   
   glActiveTexture(GL_TEXTURE1);
   glBindTexture(GL_TEXTURE_2D, texture_id2);
   

   但我更喜欢最后设置的活动单位是0 ...

   glActiveTexture(GL_TEXTURE1);
   glBindTexture(GL_TEXTURE_2D, texture_id2);
   
   glActiveTexture(GL_TEXTURE0);
   glBindTexture(GL_TEXTURE_2D, texture_id);
   

   当您开始将代码与单个纹理单元代码组合时，这将为您省去很多麻烦...也希望您出于同样的原因正确地取消绑定使用的纹理单元...

2. 你在经度 0/360 度的边缘有丑陋的接缝

   这可能是由于计算错误的光照法线、错误的非无缝纹理或只是忘记为最后一个补丁复制具有正确纹理坐标的边缘点。见：

   • Applying map of the earth texture a Sphere

   您还可以为您的星球添加大气、凹凸地图、云：

   • Bump-map a sphere with a texture map

3. Andrea 是对的……

   将矩阵设置为单位矩阵并在z=0.0 上渲染(+/-)1.0 矩形@ +/- 纵横比校正，无需深度测试、面部剔除和深度写入……这样您就可以避免因浮点错误而导致的抖动和闪烁.

4. Skybox 更好，但还有其他选项可以增强

   • Is it possible to make realistic n-body solar system simulation in matter of size and mass?

   以及其中的所有子链接，尤其是星星。您可以将天空盒和恒星目录组合在一起等等...