Main file to create a transparency window + transparency framebuffer using GLFW. This sample only draws a rotating rectangle.

transparency_glfw.cpp

#include <windows.h>
#include <GLFW/glfw3.h>
#include <iostream>

// change this to int main() to allow the console
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, char*, int nShowCmd)
{
  GLFWwindow* window;
  int windowSizeW = 640, windowSizeH = 480;
  // initialize the library
  if (!glfwInit())
    return -1;

  glfwWindowHint(GLFW_TRANSPARENT_FRAMEBUFFER, GLFW_TRUE);
  int count, windowWidth, windowHeight, monitorX, monitorY;

  // I am assuming that main monitor is in the 0 position
  GLFWmonitor** monitors = glfwGetMonitors(&count);
  const GLFWvidmode* videoMode = glfwGetVideoMode(monitors[0]);
  // width: 75% of the screen
  windowWidth = static_cast<int>(videoMode->width / 1.5);
  // aspect ratio 16 to 9
  windowHeight = static_cast<int>(videoMode->height / 16 * 9);

  glfwGetMonitorPos(monitors[0], &monitorX, &monitorY);

  // set the visibility window hint to false for subsequent window creation
  glfwWindowHint(GLFW_VISIBLE, GLFW_FALSE);

  // create a windowed mode window and its OpenGL context
  window = glfwCreateWindow(windowSizeW, windowSizeH, "Hello World", NULL, NULL);
  if (!window)
  {
    glfwTerminate();
    return -1;
  }

  // make the window's context current
  glfwMakeContextCurrent(window);

  // reset the window hints to default
  glfwDefaultWindowHints();

  glfwSetWindowPos(window,
    monitorX + (videoMode->width - windowWidth) / 2,
    monitorY + (videoMode->height - windowHeight) / 2);

  // show the window
  glfwShowWindow(window);

  // uncomment following line to see the border of window
  glfwSetWindowAttrib(window, GLFW_DECORATED, GLFW_FALSE);

  float fAngle = 0.0f;
  // Loop until the user closes the window
  while (!glfwWindowShouldClose(window))
  {
    // render
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glClear(GL_COLOR_BUFFER_BIT);
    glLoadIdentity();
    glRotatef(fAngle, 0, 0, 1);
    glBegin(GL_QUADS);
    glColor3f(0, 0, 1);
    glVertex3f(-0.5, -0.5, -1);
    glColor3f(0, 1, 0);
    glVertex3f(0.5, -0.5, -1);
    glColor3f(1, 0, 1);
    glVertex3f(0.5, 0.5, -1);
    glColor3f(1, 1, 0);
    glVertex3f(-0.5, 0.5, -1);
    glEnd();

    fAngle += 0.01;  // at some point this will explote! overflow: put the corresponding of

    // swap front and back buffers
    glfwSwapBuffers(window);

    // poll for and process events
    glfwPollEvents();
  }

  glfwTerminate();
  return 0;
}

I try to delete the line 52: glfwSetWindowAttrib(window, GLFW_DECORATED, GLFW_FALSE);
Then the program shows the border of the window, fine.
However, It turns out that the graphic seems to have ghosts that overlap with each other.
How can I just keep the transparency of the client area without any ghosts?

I try to delete the line 52: glfwSetWindowAttrib(window, GLFW_DECORATED, GLFW_FALSE);
Then the program shows the border of the window, fine.
However, It turns out that the graphic seems to have ghosts that overlap with each other.
How can I just keep the transparency of the client area without any ghosts?

Ummm honestly , without tested it, it could be related for the glfwWindowHint(GLFW_TRANSPARENT_FRAMEBUFFER function. Try to set it again.