glfwGetWin32Window returns NULL handle

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1

Trying to embed glfw window inside windows forms.
Below is the pseudo code used to create glfw window
…
#define GLFW_EXPOSE_NATIVE_WGL
#define GLFW_EXPOSE_NATIVE_WIN32
…
window = glfwCreateWindow( 1024, 768, “Tutorial 01”, NULL, NULL);
glfwMakeContextCurrent(window);
hWnd = glfwGetWin32Window(window);

hWnd is NULL.Should I set any other preprocessor definitions to retrieve handle pointer?

Building a CAD application using VC++ and Glfw for opengl

Can you also direct me to any other implementation samples using VC++ and glfw?

Thanks in advance.

2

This works for me.

I compiled from source on Windows with VS2017 using cmake, and ran the Debug Win32 build of simple.c altered to add the define and include for native access after the glfw3 include as:

#include <GLFW/glfw3.h>

#define GLFW_EXPOSE_NATIVE_WGL
#define GLFW_EXPOSE_NATIVE_WIN32 
#include <GLFW/glfw3native.h>

And then after the window creation I added the call to g the hWnd:

    window = glfwCreateWindow(640, 480, "Simple example", NULL, NULL);
    if (!window)
    {
        glfwTerminate();
        exit(EXIT_FAILURE);
    }
	HWND hWnd = glfwGetWin32Window(window);

This worked for me. Perhaps you can try this? Full file for simple.c as I used below:

//========================================================================
// Simple GLFW example
// Copyright (c) Camilla Löwy <elmindreda@glfw.org>
//
// This software is provided 'as-is', without any express or implied
// warranty. In no event will the authors be held liable for any damages
// arising from the use of this software.
//
// Permission is granted to anyone to use this software for any purpose,
// including commercial applications, and to alter it and redistribute it
// freely, subject to the following restrictions:
//
// 1. The origin of this software must not be misrepresented; you must not
//    claim that you wrote the original software. If you use this software
//    in a product, an acknowledgment in the product documentation would
//    be appreciated but is not required.
//
// 2. Altered source versions must be plainly marked as such, and must not
//    be misrepresented as being the original software.
//
// 3. This notice may not be removed or altered from any source
//    distribution.
//
//========================================================================
//! [code]

#include <glad/glad.h>
#include <GLFW/glfw3.h>

#define GLFW_EXPOSE_NATIVE_WGL
#define GLFW_EXPOSE_NATIVE_WIN32
#include <GLFW/glfw3native.h>

#include "linmath.h"

#include <stdlib.h>
#include <stdio.h>

static const struct
{
    float x, y;
    float r, g, b;
} vertices[3] =
{
    { -0.6f, -0.4f, 1.f, 0.f, 0.f },
    {  0.6f, -0.4f, 0.f, 1.f, 0.f },
    {   0.f,  0.6f, 0.f, 0.f, 1.f }
};

static const char* vertex_shader_text =
"#version 110\n"
"uniform mat4 MVP;\n"
"attribute vec3 vCol;\n"
"attribute vec2 vPos;\n"
"varying vec3 color;\n"
"void main()\n"
"{\n"
"    gl_Position = MVP * vec4(vPos, 0.0, 1.0);\n"
"    color = vCol;\n"
"}\n";

static const char* fragment_shader_text =
"#version 110\n"
"varying vec3 color;\n"
"void main()\n"
"{\n"
"    gl_FragColor = vec4(color, 1.0);\n"
"}\n";

static void error_callback(int error, const char* description)
{
    fprintf(stderr, "Error: %s\n", description);
}

static void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods)
{
    if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
        glfwSetWindowShouldClose(window, GLFW_TRUE);
}

int main(void)
{
    GLFWwindow* window;
    GLuint vertex_buffer, vertex_shader, fragment_shader, program;
    GLint mvp_location, vpos_location, vcol_location;

    glfwSetErrorCallback(error_callback);

    if (!glfwInit())
        exit(EXIT_FAILURE);

    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 2);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);

    window = glfwCreateWindow(640, 480, "Simple example", NULL, NULL);
    if (!window)
    {
        glfwTerminate();
        exit(EXIT_FAILURE);
    }
	HWND hWnd = glfwGetWin32Window(window);

    glfwSetKeyCallback(window, key_callback);

    glfwMakeContextCurrent(window);
    gladLoadGLLoader((GLADloadproc) glfwGetProcAddress);
    glfwSwapInterval(1);

    // NOTE: OpenGL error checks have been omitted for brevity

    glGenBuffers(1, &vertex_buffer);
    glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    vertex_shader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertex_shader, 1, &vertex_shader_text, NULL);
    glCompileShader(vertex_shader);

    fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragment_shader, 1, &fragment_shader_text, NULL);
    glCompileShader(fragment_shader);

    program = glCreateProgram();
    glAttachShader(program, vertex_shader);
    glAttachShader(program, fragment_shader);
    glLinkProgram(program);

    mvp_location = glGetUniformLocation(program, "MVP");
    vpos_location = glGetAttribLocation(program, "vPos");
    vcol_location = glGetAttribLocation(program, "vCol");

    glEnableVertexAttribArray(vpos_location);
    glVertexAttribPointer(vpos_location, 2, GL_FLOAT, GL_FALSE,
                          sizeof(vertices[0]), (void*) 0);
    glEnableVertexAttribArray(vcol_location);
    glVertexAttribPointer(vcol_location, 3, GL_FLOAT, GL_FALSE,
                          sizeof(vertices[0]), (void*) (sizeof(float) * 2));

    while (!glfwWindowShouldClose(window))
    {
        float ratio;
        int width, height;
        mat4x4 m, p, mvp;

        glfwGetFramebufferSize(window, &width, &height);
        ratio = width / (float) height;

        glViewport(0, 0, width, height);
        glClear(GL_COLOR_BUFFER_BIT);

        mat4x4_identity(m);
        mat4x4_rotate_Z(m, m, (float) glfwGetTime());
        mat4x4_ortho(p, -ratio, ratio, -1.f, 1.f, 1.f, -1.f);
        mat4x4_mul(mvp, p, m);

        glUseProgram(program);
        glUniformMatrix4fv(mvp_location, 1, GL_FALSE, (const GLfloat*) mvp);
        glDrawArrays(GL_TRIANGLES, 0, 3);

        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    glfwDestroyWindow(window);

    glfwTerminate();
    exit(EXIT_SUCCESS);
}

//! [code]
2 Likes
3

Thank you so much for a very quick help dougbinks.

It returns NULL even after order change.
I am using VisualStudio2012, build using visual studio build(not cmake) win32 debug mode.

Please find my code below:

// Include standard headers
#include <stdio.h>
#include <stdlib.h>

// Include GLEW
#include <GL/glew.h>

// Include GLFW
#include <glfw3.h>
#define GLFW_EXPOSE_NATIVE_WGL
#define GLFW_EXPOSE_NATIVE_WIN32 
#include <glfw3native.h>

GLFWwindow* window;
HWND hWnd;

// Include GLM
#include <glm/glm.hpp>
using namespace glm;

int OpenGLWindowInit(HWND parentHandle)
{
	// Initialise GLFW
	if( !glfwInit() )
	{
		fprintf( stderr, "Failed to initialize GLFW\n" );
		getchar();
		return -1;
	}

	glfwWindowHint(GLFW_SAMPLES, 4);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
	glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); // To make MacOS happy; should not be needed
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
	glfwWindowHint(GLFW_DECORATED,GL_FALSE);
	glfwWindowHint(GLFW_VISIBLE,GL_FALSE);

	// Open a window and create its OpenGL context
	window = glfwCreateWindow( 1024, 768, "Tutorial 01", NULL, NULL);
	if( window == NULL ){
		fprintf( stderr, "Failed to open GLFW window. If you have an Intel GPU, they are not 3.3 compatible. Try the 2.1 version of the tutorials.\n" );
		getchar();
		glfwTerminate();
		return -1;
	}

	glfwMakeContextCurrent(window);
	
	hWnd = glfwGetWin32Window(window);

	if(!hWnd)
	{
		SetParent(hWnd, parentHandle);
		LONG nNewStyle = GetWindowLong(hWnd, GWL_STYLE) & ~WS_POPUP |WS_CHILDWINDOW;
		SetWindowLong(hWnd, GWL_STYLE, nNewStyle);
		glfwShowWindow(window);		
	}

Thanks once again.

4

Update: Returns NULL

I tried sample code which you provided, simplified it much more as shown below.
Excluded everything related to glad.h as I wanted to check return value of glfwGetWin32Window()

Please find the below code:

#include <glfw3.h>
#define GLFW_EXPOSE_NATIVE_WGL
#define GLFW_EXPOSE_NATIVE_WIN32
#include <glfw3native.h>

#include "linmath.h"

#include <stdlib.h>
#include <stdio.h>

static const struct
{
    float x, y;
    float r, g, b;
} vertices[3] =
{
    { -0.6f, -0.4f, 1.f, 0.f, 0.f },
    {  0.6f, -0.4f, 0.f, 1.f, 0.f },
    {   0.f,  0.6f, 0.f, 0.f, 1.f }
};

static const char* vertex_shader_text =
"#version 110\n"
"uniform mat4 MVP;\n"
"attribute vec3 vCol;\n"
"attribute vec2 vPos;\n"
"varying vec3 color;\n"
"void main()\n"
"{\n"
"    gl_Position = MVP * vec4(vPos, 0.0, 1.0);\n"
"    color = vCol;\n"
"}\n";

static const char* fragment_shader_text =
"#version 110\n"
"varying vec3 color;\n"
"void main()\n"
"{\n"
"    gl_FragColor = vec4(color, 1.0);\n"
"}\n";

static void error_callback(int error, const char* description)
{
    fprintf(stderr, "Error: %s\n", description);
}

static void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods)
{
    if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
        glfwSetWindowShouldClose(window, GLFW_TRUE);
}

void OpenGLWindowInit()
{
    GLFWwindow* window;
    GLuint vertex_buffer, vertex_shader, fragment_shader, program;
    GLint mvp_location, vpos_location, vcol_location;

    glfwSetErrorCallback(error_callback);

    if (!glfwInit())
        exit(EXIT_FAILURE);

    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 2);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);

    window = glfwCreateWindow(640, 480, "Simple example", NULL, NULL);
    if (!window)
    {
        glfwTerminate();
        exit(EXIT_FAILURE);
    }
	HWND hWnd = glfwGetWin32Window(window);

    glfwSetKeyCallback(window, key_callback);

    glfwMakeContextCurrent(window);

    glfwDestroyWindow(window);

    glfwTerminate();
    exit(EXIT_SUCCESS);
}

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5

Thankfully you included a screenshot of your debugging, since it turns out that glfwGetWin32Window() is actually returning a value, not NULL. In the case about it’s returning 0x000c0604 which is likely a valid window handle (for example, on my test I have 0x000c078e).

Try using this window handle, for example add a call to ShowWindow and minimize as below:

	HWND hWnd = glfwGetWin32Window(window);
	ShowWindow( hWnd, SW_MINIMIZE );

This should minimize the window (iconify it).

So it looks like this was working all along, except perhaps you thought the value of hWnd would be something you would see the debug contents of, like a pointer to a struct. However it’s an opaque handle.

2 Likes
6

Yes.This was exactly what I thought.

Thanks for clearing my confusion.I will check how to use opaque handles.