OpenGL：如何改变每个顶点的颜色？

Question

I am trying to change the color of the vertices of each triangle that I have created using the following code:

This is the Point structure; this structure stores the position data and color data of each vertex:

struct Point{
    float x;
    float y;
    float z;
    float r;
    float g;
    float b;
};

Here is created the main triangle of the Sierpinski's triangle; I created a vector that contains all the vertex data, and then the data is loaded into the buffer:

Point A, B, C;
A = {0.0f, 0.9f, 0.0f, 1.0f, 0.0f, 0.0f};
B = {0.9f, -0.9f, 0.0f, 0.0f, 1.0f, 0.0f};
C = {-0.9f, -0.9f, 0.0f, 0.0f, 0.0f, 1.0f};
std::vector<Point> vertices;   
int depth = 6;    
draw_triangles(A, B, C, depth, vertices);
      
Point vertices2[vertices.size()];
for(int i = 0;i<vertices.size();i++){
    vertices2[i] = vertices[i];
}
    
unsigned int VAO, VBO;
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);

glBindVertexArray(VAO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices2), vertices2, GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);

glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float), (void*)(3* sizeof(float)));
glEnableVertexAttribArray(1);
glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);

This function generates all the vertex data, and stores the position data of each vertex in the vertices vector:

void draw_triangles(Point A, Point B, Point C, int depth, std::vector<Point>& vertices){
    if(depth == 0) return;
    
    Point X = {(((B.x + C.x)/2) + B.x)/2, (B.y + A.y)/2, 0.0f, 1.0f, 0.0f, 0.0f};
    Point Y = {(B.x + C.x) / 2, B.y, 0.0f, 0.0f, 1.0f, 0.0f};
    Point Z = Z = {(((B.x + C.x)/2) + C.x)/2, (B.y + A.y)/2, 0.0f, 0.0f, 0.0f, 1.0f};
   
    vertices.push_back(X);
    vertices.push_back(Y);
    vertices.push_back(Z);
    
    depth--; 
    draw_triangles(A, X, Z, depth, vertices);
    draw_triangles(A, X, Z, depth, vertices);
    draw_triangles(X, B, Y, depth, vertices);
    draw_triangles(Z, Y, C, depth, vertices);
}

when the code draws, I get the following output:

My question is: How can I change the color of each vertex?

For example, the red vertex, change it to blue, the green one to red, the blue one to green and so on, generating a kind of animation.

Edit

In the code, the color is set, but what I really want is that the color of each vertex change over the time.

Answer 1

When you want to change the color of your vertices over time, you probably want to modify it frame by frame as in the example at the following link:

https://godbolt.org/z/Y1brGx

I have set up a simple way of making those structures change their values during the rendering loop; you can get [more] creative with that once you got the idea. What is important is that you update the data in your structures and you load the new data in the vertex buffer object at each frame, so that the vertex shader and the fragment shader can read the new values.

Note that you can make the colors change during each frame in different ways; another idea could be using random numbers to set the colors' components.

As a side note, you should be able to pass vertices.data() to glBufferData as a pointer to your vertex data, and avoid declaring an array of Point s for it.