c++ - 如何在顶点着色器中使用 VBO 数据作为位置数据，在片段着色器中使用统一数据作为颜色数据

Question

这是我的代码，它们是从《OpenGL Programming Guide》一书中的代码转换而来的:

GLuint VAOs,Buffers;
void init(){
   glGenVertexArrays(1, VAOs);
   glBindVertexArray(VAOs);
   GLfloat vertices[6][2] = {
        {-0.9f,-0.9f},
        {0.85f,-0.90f},
        {-0.90f, 0.85f},
        {0.90f, -0.85f},
        {0.90f,0.90f},
        {-0.85f, 0.90f}
    };
    glGenBuffers(1, Buffers);
    glBindBuffer(GL_ARRAY_BUFFER, Buffers);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);


    ShaderInfo shaders[] = { {GL_VERTEX_SHADER, "triangles.vert"},{GL_FRAGMENT_SHADER, "triangles.frag"} ,{GL_NONE, NULL} };

    program = LoadShaders(shaders); 

    GLuint pos = glGetAttribLocation(program, "vposition");
    glVertexAttribPointer(pos, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
    glEnableVertexAttribArray(pos);

    GLuint index,b;
    char *name[]={"color"};
    GLfloat fcolor[4]={1.0,0.0,0.0,1.0};
    glGetUniformIndices(program,1,(const char**)name,&index);
    glGenBuffers(1, &b);
    glBindBuffer(GL_UNIFORM_BUFFER, Buffers[ArrayBuffer]);
    glBufferData(GL_UNIFORM_BUFFER, sizeof(fcolor), fcolor, GL_STATIC_DRAW);
    glBindBufferBase(GL_UNIFORM_BUFFER, index, b);

    glUseProgram(program);
}

这是顶点着色器:

#version 430 core
uniform vec4 fcolor;
layout(location=3)in vec4 vposition;
void
main()
{
    vec4 p = vposition;
    gl_Position = p;
}

这是片段着色器:

#version 430 core
uniform vec4 color;
out vec4 fColor;
void
main()
{
    fColor = color;
}

我以为黑底红三角，其实只有一个黑色的窗口。我不知道为什么，请帮助我!

Answer 1

uniform vec4 color; 不是 Uniform block (另见 Uniform Buffer Object )。
它只是一个 Uniform变量(在默认统一 block 内)。所以你必须使用 glUniform*设置值。

glUseProgram(program);
glUniform4fv(index, 1, fcolor);

代码中的另一个错误是本应作为数组缓冲区的缓冲区对象 (Buffers[ArrayBuffer]) 绑定(bind)到目标 GL_UNIFORM_BUFFER。统一缓冲对象可能是b:

glBindBuffer(GL_UNIFORM_BUFFER, Buffers[ArrayBuffer]);

glBindBuffer(GL_UNIFORM_BUFFER, b);

---

当然你可以使用一个命名的Uniform Buffer .在示例中 Binding point由 Layout Qualifier 设置.例如:

#version 430 core

layout (std140, binding = 1) uniform UB_color
{
   vec4 color;
};

out vec4 fColor;

void main()
{
    fColor = color;
}

GLuint ubo;
glGenBuffers(1, &ubo);
glBindBuffer(GL_UNIFORM_BUFFER, ubo);
glBufferData(GL_UNIFORM_BUFFER, sizeof(fcolor), fcolor, GL_STATIC_DRAW);
glBindBufferBase(GL_UNIFORM_BUFFER, 1, ubo); // 1 because of 'binding = 1'

如果您不想通过布局限定符设置统一 block 绑定(bind)(无论出于何种原因):

layout (std140, binding = 1) uniform UB_color

layout (std140) uniform UB_color

GLuint ubo_index = glGetUniformBlockIndex(program, "UB_color");
GLuint ubo_binding = 7; // arbitrary number
glUniformBlockBinding(program, ubo_index, ubo_binding);
glBindBufferBase(GL_UNIFORM_BUFFER, ubo_binding, ubo);