c++ - OpenGL : second VBO spoiling first VBO

Question

我有一个代码，最初有一个着色器 (ourShader)、一个 VAO 和一个 VBO。它将使用 Stencil 测试渲染带有纹理立方体的场景及其在地面上的反射。现在，我想为后处理添加一个帧缓冲区，所以我需要第二个着色器。我添加了第二个着色器 (screenShader) 和第二个 VBO。我还没有在我的绘图中使用它们，但我添加它们这一简单的事实使我的代码渲染了一个黑色的红色三角形，而不是通常的场景。

我的代码是这样的:

    Shader ourShader(string("core.vs"), string("core.frag")); // shader class creating a shader program from vertex shader and fragment shader source files.
    Shader screenShader(string("core2.vs"), string("core2.frag"));

    // Setting up attributes, VAO, VBO
    GLuint VAO;
    array<GLuint, 2> VBO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(2, &VBO[0]);

    glBindVertexArray(VAO);

    // Data for first shader and first VBO
    glBindBuffer(GL_ARRAY_BUFFER, VBO[0]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(verticesCube), verticesCube, GL_STATIC_DRAW); 

    GLint posAttribLoc = glGetAttribLocation(ourShader.Program, "position");
    glVertexAttribPointer(posAttribLoc, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0); // specify (to the active VAO) how to retrieve the values for the attribute "position" from the data stored ("vertices" here) on the active VBO (GPU)
    glEnableVertexAttribArray(posAttribLoc); // enable attribute for rendering

    GLint colAttribLoc = glGetAttribLocation(ourShader.Program, "color");
    glVertexAttribPointer(colAttribLoc, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
    glEnableVertexAttribArray(colAttribLoc);

    GLint texAttribLoc = glGetAttribLocation(ourShader.Program, "texCoord");
    glVertexAttribPointer(texAttribLoc, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(6 * sizeof(GLfloat)));
    glEnableVertexAttribArray(texAttribLoc);

    // ##### PART GIVING A WEIRD RESULT #####
    // Data for second shader and second VBO
    glBindBuffer(GL_ARRAY_BUFFER, VBO[1]);
    glBufferData(GL_ARRAY_BUFFER, sizeof(verticesRectangle), verticesRectangle, GL_STATIC_DRAW);

    GLint posAttribLoc2 = glGetAttribLocation(screenShader.Program, "position");
    glVertexAttribPointer(posAttribLoc2, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(GLfloat), (GLvoid*)0); // specify (to the active VAO) how to retrieve the values for the attribute "position" from the data stored ("vertices" here) on the active VBO (GPU)
    glEnableVertexAttribArray(posAttribLoc2); // enable attribute for rendering

    GLint texAttribLoc2 = glGetAttribLocation(screenShader.Program, "texCoord");
    glVertexAttribPointer(texAttribLoc2, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(GLfloat), (GLvoid*)(2 * sizeof(GLfloat)));
    glEnableVertexAttribArray(texAttribLoc2);
   // ##### END #####

    // Setting up texture that will be used for the first shader
    GLuint texture;
    int width, height;
    glGenTextures(1, &texture);
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, texture); // makes "texture" the current texture and attaches it to texture unit 0

    // Set the wrapping 
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT); 
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);

    // Set the filtering 
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); 
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    unsigned char* image = SOIL_load_image("res/images/image1.jpg", &width, &height, 0, SOIL_LOAD_RGBA);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, image);
    glGenerateMipmap(GL_TEXTURE_2D);
    SOIL_free_image_data(image);

    // Unbind VBO, texture before main loop
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindTexture(GL_TEXTURE_2D, 0); 
    glfwSwapInterval(1);
    glfwSetKeyCallback(window, Input::keyCallback); // Input is a singleton class handling inputs. It works well.
    glfwSetCursorPosCallback(window, Input::mouseCallback);
    glfwSetScrollCallback(window, Input::scrollCallback);

    while (glfwWindowShouldClose(window) == GLFW_FALSE) {
        // MAIN LOOP
        // ...
    }
    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(2, &VBO[0]);

我认为主循环并不重要。我想说的是，如果我删除处理第二个 VBO 的几行代码，那么场景渲染得很好。否则，我会得到一个颜色怪异的三角形。

我的两个着色器将这些源文件用于它们各自的顶点着色器和片段着色器。顺便说一下，我的着色器没有编译错误。

核心对比:

#version 330 core
in vec3 position;
in vec2 texCoord;
in vec3 color;

out vec2 TexCoord;
out vec3 Color;

uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;

void main()
{
    gl_Position = projection*view*model*vec4(position, 1.0);
    TexCoord = vec2(texCoord.x, 1.0 - texCoord.y);
    Color = color;
}

核心片段:

#version 330 core
in vec2 TexCoord;
in vec3 Color;

out vec4 outColor;
uniform sampler2D ourTexture0;

void main()
{
    outColor = vec4(Color, 1)*texture(ourTexture0, TexCoord);
}

核心2.vs:

#version 330 core
in vec2 position;
in vec2 texCoord;
out vec2 TexCoord;
void main()
{
    gl_Position = vec4(position, 0.0, 1.0);
    TexCoord = texCoord;
}

核心2.片段:

#version 330 core
in vec2 TexCoord;
out vec4 outColor;
uniform sampler2D texFramebuffer;
void main()
{
    outColor = texture(texFramebuffer, TexCoord);
}

顶点看起来像这样(但只有阅读它们的方式很重要):

    GLfloat verticesRectangle[] = {
        // position     // texture coordinates
        -0.5f, -0.5f,   0.0f, 0.0f,     
        0.5f, -0.5f,    1.0f, 0.0f,     
        -0.5f, 0.5f,    0.0f, 1.0f,     
        0.5f, 0.5f,     1.0f, 1.0f      
    };

    GLfloat verticesCube[] = {
        // position          // color          // texture coordinates
        -0.5f, -0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 0.0f,
        0.5f, -0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 1.0f, 0.0f,
        0.5f,  0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f,
        0.5f,  0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f,
        -0.5f,  0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 1.0f,
        -0.5f, -0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 0.0f,

        -0.5f, -0.5f,  0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 0.0f,
        0.5f, -0.5f,  0.5f, 1.0f, 1.0f, 1.0f, 1.0f, 0.0f,
        0.5f,  0.5f,  0.5f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f,
        0.5f,  0.5f,  0.5f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f,
        -0.5f,  0.5f,  0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 1.0f,
        -0.5f, -0.5f, 0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 0.0f,

        -0.5f, 0.5f, 0.5f, 1.0f, 1.0f, 1.0f, 1.0f, 0.0f,
        -0.5f, 0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f,
        -0.5f, -0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 1.0f,
        -0.5f, -0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 1.0f,
        -0.5f, -0.5f, 0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 0.0f,
        -0.5f, 0.5f, 0.5f, 1.0f, 1.0f, 1.0f, 1.0f, 0.0f,

        0.5f, 0.5f, 0.5f, 1.0f, 1.0f, 1.0f, 1.0f, 0.0f,
        0.5f, 0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f,
        0.5f, -0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 1.0f,
        0.5f, -0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 1.0f,
        0.5f, -0.5f, 0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 0.0f,
        0.5f, 0.5f, 0.5f, 1.0f, 1.0f, 1.0f, 1.0f, 0.0f,

        -0.5f, -0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 1.0f,
        0.5f, -0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f,
        0.5f, -0.5f, 0.5f, 1.0f, 1.0f, 1.0f, 1.0f, 0.0f,
        0.5f, -0.5f, 0.5f, 1.0f, 1.0f, 1.0f, 1.0f, 0.0f,
        -0.5f, -0.5f, 0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 0.0f,
        -0.5f, -0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 1.0f,

        -0.5f, 0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 1.0f,
        0.5f, 0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f,
        0.5f, 0.5f, 0.5f, 1.0f, 1.0f, 1.0f, 1.0f, 0.0f,
        0.5f, 0.5f, 0.5f, 1.0f, 1.0f, 1.0f, 1.0f, 0.0f,
        -0.5f, 0.5f, 0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 0.0f,
        -0.5f, 0.5f, -0.5f, 1.0f, 1.0f, 1.0f, 0.0f, 1.0f,

        -1.0f, -0.5f, 1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, // reflection surface // not a part of the cube itself
        -1.0f, -0.5f, -1.0f, 0.0f, 0.0f, 0.0f, 1.0f, 1.0f,
        1.0f, -0.5f, 1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f,
        1.0f, -0.5f, -1.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f,
        -1.0f, -0.5f, -1.0f, 0.0f, 0.0f, 0.0f, 1.0f, 1.0f,
        1.0f, -0.5f, 1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f
    };

我已经看过 Binding a second vertex buffer seems to spoil my first vertex buffer, OpenGL OES ios 5.1但是这个人有这个问题是因为他没有正确使用他的 VAO。

Answer 1

很可能您的两个属性位置具有相同的值。由于您只使用一个 VAO，因此您覆盖了一些绑定(bind)。使用多个独立几何体的正确方法是在每个几何体上使用 VAO。

正确的代码应该是这样的:

glBindVertexArray(vao1);
glBindBuffer(VBO[0])
glVertexAttribPointer...
glEnableVertexAttribArray...
//Setup all attributes for first VBO

glBindVertexArray(vao2);
glBindBuffer(VBO[1])
glVertexAttribPointer...
glEnableVertexAttribArray...
//Setup all attributes for second VBO

渲染时执行以下操作:

glBindVertexArray(vao1);
glDraw*... //Draw VAO1

glBindVertexArray(vao2);
glDraw*.... //Draw VAO2