c++ - 如何在现代openGL中用3D点绘制多边形？

Question

我知道在2.0-openGL中，我们可以像这样简单地画一条线。

glBegin(GL_LINES);  
glVertex3f(20.0f,150.0f,0.0f);  
glVertex3f(220.0f,150.0f,0.0f);  
glVertex3f(200.0f,160.0f,0.0f);  
glVertex3f(200.0f,160.0f,0.0f);  
glEnd();

但是如何在现代openGL（3.0+）中做类似的事情

我已经读过 Drawing round points using modern OpenGL，但是答案不是关于某个点的，因为我想用点绘制具有一定坐标的多边形，所以并没有太大帮助。

我使用此代码，但除了蓝色背景外什么都没有显示。我错过了什么？

GLuint VertexArrayID;
    glGenVertexArrays(1, &VertexArrayID);
    glBindVertexArray(VertexArrayID);

static const GLfloat g_vertex_buffer_data[] = {
        20.0f, 150.0f, 0.0f, 1.0f,
            220.0f, 150.0f, 0.0f, 1.0f,
            200.0f, 160.0f, 0.0f, 1.0f
    };

GLuint vertexbuffer;
glGenBuffers(1, &vertexbuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW);

do{

    // Clear the screen
    glClear( GL_COLOR_BUFFER_BIT );

    // 1rst attribute buffer : vertices
    glEnableVertexAttribArray(0);
    glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
    glVertexAttribPointer(
        0,                  // attribute 0. No particular reason for 0, but must match the layout in the shader.
        4,                  // size
        GL_FLOAT,           // type
        GL_FALSE,           // normalized?
        0,                  // stride
        (void*)0            // array buffer offset
    );

    // Draw the triangle !
    glDrawArrays(GL_LINES, 0, 2); // 3 indices starting at 0 -> 1 triangle

    glDisableVertexAttribArray(0);

    // Swap buffers
    glfwSwapBuffers(window);


} // Check if the ESC key was pressed or the window was closed
while( glfwGetKey(window, GLFW_KEY_ESCAPE ) != GLFW_PRESS &&
       glfwWindowShouldClose(window) == 0 );

Answer 1

1）您必须定义一个顶点数组，其中包含多边形线的点。如您的示例：

GLfloat vertices[] =
{
    20.0f, 150.0f, 0.0f, 1.0f,
    220.0f, 150.0f, 0.0f, 1.0f,
    200.0f, 160.0f, 0.0f, 1.0f
};

2）您必须定义并绑定一个顶点缓冲对象（VBO），才能将您的 vertices传递给顶点着色器。像这样：

// This is the identifier for your vertex buffer
GLuint vbo;
// This creates our identifier and puts it in vbo
glGenBuffers(1, &vbo);
// This binds our vbo
glBindBuffer(GL_ARRAY_BUFFER, vbo);
// This hands the vertices into the vbo and to the rendering pipeline    
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

3）现在我们可以绘制了。这样做：

// "Enable a port" to the shader pipeline
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
// pass information about how vertex array is composed
glVertexAttribPointer(0, // same as in glEnableVertexAttribArray(0)
                      4, // # of coordinates that build a vertex
                      GL_FLOAT, // data type
                      GL_FALSE, // normalized?
                      0,        // stride
                      (void*)0);// vbo offset

glDrawArrays(GL_LINES, 0, 2);
glDisableVertexAttribArray(0);

步骤1）和2）可以在呈现为初始化之前完成。步骤3）在渲染循环中完成。另外，您将需要一个顶点着色器和一个片段着色器以使颜色可视化。

如果您对这些事情一无所知，并且想从OpenGL 3开始，那么我建议从这样的教程重新开始：
http://www.opengl-tutorial.org/beginners-tutorials/tutorial-1-opening-a-window/