My goal is get pixel data from main window. nothing any rendering.
like we see the monitor such as screencapture.
I tried to TRANSPARENT windows, glReadPixel.
so I have a TRANSPARENT windows and context.
glfwSetErrorCallback(errorCallback);
if (!glfwInit()) {
std::cerr << "Error: GLFW " << std::endl;
exit(EXIT_FAILURE);
}
glfwWindowHint(GLFW_DEPTH_BITS, 16);
glfwWindowHint(GLFW_TRANSPARENT_FRAMEBUFFER, GLFW_TRUE);
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
glfwWindowHint(GLFW_SAMPLES, 4);
const int Monitor_count = GetMonitors();
GLwindow = glfwCreateWindow(
nWidth, // width
nHeight, // height
"OpenGL_Test", // window title
NULL, NULL);
if (!GLwindow) {
glfwTerminate();
exit(EXIT_FAILURE);
}
glfwSwapInterval(1);
//glfwShowWindow(GLwindow);
if (glfwGetWindowAttrib(GLwindow, GLFW_TRANSPARENT_FRAMEBUFFER))
{
// ..
}
glfwSetWindowOpacity(GLwindow, 0.0f);
glfwMakeContextCurrent(GLwindow);
glfwSetKeyCallback(GLwindow, keyCallback);
glewExperimental = GL_TRUE;
GLenum errorCode = glewInit();
But I want get pixel data from GPU without create windows.
So I use wglcreatecontext Get mother window DC, HGLRC.
And When I set bind buffer, It gives runtime error.
if (!glfwInit()) {
std::cerr << "Error: GLFW" << std::endl;
exit(EXIT_FAILURE);
}
HDCC = GetDC(m_hWndCopy);
// HDC TDC = CreateCompatibleDC(HDCC);
HGLRC DC = wglCreateContext(HDCC);
GLuint pbo;
glGenBuffersARB(1, &pbo); <<Error Here
glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pbo);
How can I solve problem?
Any idea or link?
From your question and comment replies I gather, that you want to use OpenGL to grab a screenshot of an arbitrary window? If so, then this is not what OpenGL is meant for. You cannot use OpenGL for taking screenshots reliably.
glReadPixels will work reliably only for things that you did draw with OpenGL in the first place!
Related
When I started I used the GLFW example code:
#include <GLFW/glfw3.h>
int main(void)
{
GLFWwindow* window;
/* Initialize the library */
if (!glfwInit())
return -1;
/* Create a windowed mode window and its OpenGL context */
window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL);
if (!window)
{
glfwTerminate();
return -1;
}
/* Make the window's context current */
glfwMakeContextCurrent(window);
/* Loop until the user closes the window */
while (!glfwWindowShouldClose(window))
{
/* Render here */
glClear(GL_COLOR_BUFFER_BIT);
/* Swap front and back buffers */
glfwSwapBuffers(window);
/* Poll for and process events */
glfwPollEvents();
}
glfwTerminate();
return 0;
}
When running this it gives me a black screen titled "Hello world" which is exactly what I want. But by simply adding GLAD:
#include <glad/glad.h>
#include <GLFW/glfw3.h>
...and giving window hints:
//Specify the OpenGL versions we're using
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
Suddenly it tells me the window failed to initialize.
But by simply adding this:
#ifdef __APPLE__
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif
...it allows the window to initialize but crashes when glClear(GL_COLOR_BUFFER_BIT) is called and it gives me the error
'./Voxel\ Game' terminated by signal SIGSEGV (Address boundary error)
I know this because when I remove that line it works, it just doesn't clear the screen.
This is the full code I have now in case the error is somewhere else in there:
#include <iostream>
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#define SCREEN_WIDTH 640
#define SCREEN_HIEGHT 480
int main()
{
GLFWwindow* window;
//Initialize the library
if (!glfwInit())
{
std::cout << "Failed to initalize GLFW" << std::endl;
return -1;
}
//Specify the OpenGL versions we're using
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
#ifdef __APPLE__
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif
//Create a windowed mode window and its OpenGL context
window = glfwCreateWindow(SCREEN_WIDTH, SCREEN_HIEGHT, "Voxel Game", NULL, NULL);
if (!window)
{
std::cout << "Failed create GLFW window" << std::endl;
glfwTerminate();
return -1;
}
//Make the window's context current
glfwMakeContextCurrent(window);
//Loop until the user closes the window
while (!glfwWindowShouldClose(window))
{
//Render here
//glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
//Swap front and back buffers
glfwSwapBuffers(window);
//Poll for and process events
glfwPollEvents();
}
glfwTerminate();
return 0;
}
You are not initializing glad, add gladLoadGL(glfwGetProcAddress); after glfwMakeContextCurrent() and check it returns OK.
In general, there is no OpenGL library apart from some old OpenGL1.1 stuff (in Windows at least), all those GL calls are implemented in the graphics drivers directly, GLAD library just defines a lot of function pointers and wraps them in nicer macros. Then during initialization, it will dynamically load the functions from the drivers present on the machine. Hence the need to generate GLAD for specific OpenGL version.
So if you get segfaults on some GL calls, a good guess is some of those functions were not found, maybe because they are not supported on the HW or because you did not setup GLAD/GLFW correctly.
#include "list.h"
int main()
{
//INIT GLFW
glfwInit();
//CREATE WINDOW
const int WINDOW_WIDTH = 640;
const int WINDOW_HEIGHT = 480;
int framebufferWidth = 0;
int framebufferHight = 0;
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 4);
glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
GLFWwindow* window = glfwCreateWindow(WINDOW_WIDTH,WINDOW_HEIGHT,"Title", NULL, NULL);
glfwGetFramebufferSize(window, &framebufferWidth, &framebufferHight);
glViewport(0, 0, framebufferWidth, framebufferHight);
glfwMakeContextCurrent(window);//IMPORTIANT!!
//INIT GLEW (NEEDS WINDOW AND OPENGL CONTEXT)
glewExperimental = GL_TRUE;
>//Error
if (glewInit() != GLEW_OK)
{
std::cout << "ERROR::MAIN.CPP::GLEW_INIT_FAILED" << "\n";
glfwTerminate();
}
//MAIN LOOP
while (glfwWindowShouldClose(window))
{
//UPDATE INPUT ---
//UPDATE ---
//DRAW ---
//Clear
//Draw
//End Draw
}
//END OF PROGAM
glfwTerminate();
return 0;
}
glViewport(0, 0, framebufferWidth, framebufferHight); is giving me
Unhandled exception at >0x00007FF704D6E7D9 in OpenzGL4.exe: 0xC0000005: Access violation reading >location >0x0000000000000348.
when I run it.
For any OpenGL instruction is required a valid and current OpenGL Context. Hence glfwMakeContextCurrent hast to be invoked before any OpneGL instruction:
GLFWwindow* window = glfwCreateWindow(WINDOW_WIDTH,WINDOW_HEIGHT,"Title", NULL, NULL);
glfwMakeContextCurrent(window); // <----- ADD
glfwGetFramebufferSize(window, &framebufferWidth, &framebufferHight);
glViewport(0, 0, framebufferWidth, framebufferHight);
glfwMakeContextCurrent(window); // <----- DELETE
In addition to what Rabbid76 already wrote in his answer, there is another problem in your code:
glViewport(0, 0, framebufferWidth, framebufferHight);
glfwMakeContextCurrent(window);//IMPORTIANT!!
//INIT GLEW (NEEDS WINDOW AND OPENGL CONTEXT)
glewExperimental = GL_TRUE;
>//Error
if (glewInit() != GLEW_OK) {
std::cout << "ERROR::MAIN.CPP::GLEW_INIT_FAILED" << "\n";
glfwTerminate(); }
Since you use the GLEW OpenGL loader, every gl...() Function name is actually remapped as a preprocessor macro to a function pointer, and glewInit will query all those function pointers (and that needs an active OpenGL context, so it can't be done before the glfwMakeContextCurrent). So it is not enough to move the glViewport after the glfwMakeContextCurrent, you must also move it after glewInit.
And there is a second issue with this code: the glewExperimental = GL_TRUE is an evil hack for a bug in GLEW 1.x with OpenGL core profiles, and it's use can't be discouraged enough. Just update to GLEW 2.x or another loader which is compatible with OpenGL core profile contexts.
i have a little problem setting up my glfw overlay properly, i already successfully created an glfw window with transparent background , now i want to make the window also "click-through" so i can access the windows behind it and let it act like an overlay.
sadly i cant figure out how to do this in glfw, my current code to init the window looks like that:
Width = 3440;
Height = 1440;
/* GLFW */
if (!glfwInit()) {
fprintf(stdout, "[GLFW] failed to init!\n");
exit(1);
}
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 0);
glfwWindowHint(GLFW_DECORATED, GLFW_FALSE);
glfwWindowHint(GLFW_RESIZABLE, GLFW_FALSE);
glfwWindowHint(GLFW_FOCUSED, GLFW_FALSE);
glfwWindowHint(GLFW_FOCUS_ON_SHOW, GLFW_FALSE);
/*Topmost and see through*/
glfwWindowHint(GLFW_FLOATING, GLFW_TRUE);
glfwWindowHint(GLFW_TRANSPARENT_FRAMEBUFFER, GLFW_TRUE);
glfwSwapInterval(1);
Window = glfwCreateWindow(Width, Height, "Overlay", 0, 0);
glfwMakeContextCurrent(Window);
i also tried with glfw3_native.h given glfwGetX11Window function and tried to do stuff like
void Render::MakeClickable(bool State){
auto X11Window = glfwGetX11Window(Window);
if(State){
}else{
XserverRegion region = XFixesCreateRegion (MainDisplay, NULL, 0);
XFixesSetWindowShapeRegion (MainDisplay, X11Window, ShapeInput, 0, 0, region);
XFixesDestroyRegion (MainDisplay, region);
}
}
but that didn't worked :/
How can I setup my window correctly to ignore my click and let it pass to the windows behind, so i can use it as an overlay?
a new window hint GLFW_MOUSE_PASSTHROUGH was added to GLFW recently to enable this feature.
you can use it like that:
glfwWindowHint(GLFW_MOUSE_PASSTHROUGH, GLFW_TRUE);
I'm trying to my desktop image capture. (All images, including the desktop output to the monitor)
It's easy using window API (BitBlt or CImageClass) and it's not the way I want.
I want do it using opengl. so I found glReadPixel funtion and window TRANSPARENT.
But it just read pixel own Windows application screen.(Save as bmp file and check)
Initialize()
glfwSetErrorCallback(errorCallback);
if (!glfwInit()) {
std::cerr << "Error: GLFW " << std::endl;
exit(EXIT_FAILURE);
}
glfwWindowHint(GLFW_DEPTH_BITS, 16);
glfwWindowHint(GLFW_TRANSPARENT_FRAMEBUFFER, GLFW_TRUE);
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
glfwWindowHint(GLFW_SAMPLES, 4);
const int Monitor_count = GetMonitors();
GLwindow = glfwCreateWindow(
nWidth, // width
nHeight, // height
"OpenGL_Test", // window title
NULL, NULL);
if (!GLwindow) {
glfwTerminate();
exit(EXIT_FAILURE);
}
glfwSwapInterval(1);
if (glfwGetWindowAttrib(GLwindow, GLFW_TRANSPARENT_FRAMEBUFFER))
{
//...
}
glfwSetWindowOpacity(GLwindow, 0.0f);
auto Mode = glfwGetVideoMode(Monitor[0]);
glfwMakeContextCurrent(GLwindow);
glfwSetKeyCallback(GLwindow, keyCallback);
glewExperimental = GL_TRUE;
GLenum errorCode = glewInit();
if (GLEW_OK != errorCode) {
std::cerr << "Error: GLEW - " << glewGetErrorString(errorCode) << std::endl;
glfwTerminate();
exit(EXIT_FAILURE);
}
if (!GLEW_VERSION_3_3) {
std::cerr << "OpenGL 3.3 API is not available." << std::endl;
glfwTerminate();
exit(EXIT_FAILURE);
}
glViewport(0, 0, nWidth, nHeight);
glBindFramebuffer(GL_FRAMEBUFFER, 0);
if (glCheckFramebufferStatus(GL_FRAMEBUFFER) == GL_FRAMEBUFFER_COMPLETE) {
std::cerr << "Error: " << std::endl;
}
return true;
Roop
while (!glfwWindowShouldClose(GLwindow)) {
Sleep(10);
glClearColor(0.0f, 0.3f, 0.3f, 0.5f);
glClear(GL_COLOR_BUFFER_BIT);
unsigned char *image = (unsigned char*)malloc(sizeof(unsigned char)*nWidth*nHeight * 3);
glReadPixels(0, 0, nWidth, nHeight, GL_BGR_EXT, GL_UNSIGNED_BYTE, image);
glfwPollEvents();
}
return true;
Q1. Is it possible desktop capture(Full Image GPU output) with OPENGL?
Q2. If Q1 is possible, Should I use FBO and PBO GL_BACK??
Q3. How to access to mother window or GPU adapter? >> GL seems to strongly reject this.(I don't want any rendering, just read pixel data from GPU(Desktop image. not rendered by my application.)(If it is possible ...))
Anybody shows to me about link or idea?
What you're asking for is something completely outside the scope of OpenGL. OpenGL is designed to be a platform-agnostic API for applications to talk about drawing stuff into framebuffers in an abstract fashion. OpenGL has no notion of windows*, screens, or a desktop. OpenGL doesn't operate at a level where such concepts exist. Heck, OpenGL doesn't even know what a GPU is. OpenGL is supposed to be initialized through platform-specific mechanisms to establish a context which assigns actual meaning to OpenGL API calls. As far as I know, there is no way to set up an OpenGL context with a framebuffer whose contents would somehow correspond to the desktop on Windows (or any other platform I'm aware of). As far as my understanding goes, this wouldn't really make sense…
To do what you want to do, you'll have to rely on the respective platform-specific APIs. The probably simplest way on Windows is to get an HDC for the entire desktop and BitBlt from there. See, e.g., this question for more on that. A more modern approach would be to use the DXGI Desktop Duplication API.
(*) yes, I know the OpenGL specification technically does talk about "windows" in a few places; but it only really does so when it's talking about all the things it's not responsible for…
I'm trying to my desktop image capture. (All images, including the desktop output to the monitor)
It's easy using window API (BitBlt or CImageClass) and it's not the way I want.
But it's the way it's supposed to be done.
I want do it using opengl. so I found glReadPixel funtion
You can't. OpenGL doesn't "know" about the desktop, or other windows (or actually what windows are at all). The function glReadPixels will work reliably only for images that have been drawn with OpenGL itself.
You can't use OpenGL to take screenshots! On older computers it might seem to work, but that's only because of their older memory management where when you create a new window, its memory will be "cut" from what was below and if you read that, it looks like a way to make screenshots. But it is not.
I'm trying to run my first opengl program in C++, which opens a window, sets a background color, and gives a title, from Terminal on Mac OS X.
The code compiles and links fine. When I run the program the window and title open fine but the background color is always black.
It is my understanding that the function glClearColor sets the background color. However, no matter what parameters I pass to the function, the background color of the window is always black.
If anyone can explain to me what errors I'm making, I would very much appreciate it. Thanks and below is the code:
#include <iostream>
#define GLEW_STATIC
#include <GL/glew.h>
#include <GLFW/glfw3.h>
const GLint WIDTH = 800, HEIGHT = 600;
int main()
{
glfwInit();
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
GLFWwindow* window = glfwCreateWindow(WIDTH, HEIGHT, "Learn OpenGL", nullptr, nullptr);
int screenWidth, screenHeight;
glfwGetFramebufferSize(window, &screenWidth, &screenHeight);
if(nullptr == window)
{
std::cout << "Failed to create GLFW window" << '\n';
glfwTerminate();
return -1;
}
glewExperimental = GL_TRUE;
GLenum err=glewInit();
if(err != glewInit())
{
std::cout << "Failed to initialize GLEW" << '\n';
return -1;
}
glViewport(0, 0, screenWidth, screenHeight);
while(!glfwWindowShouldClose(window))
{
glfwPollEvents();
glClearColor(0.2f, 0.2f, 0.9f, 0.5f);
glClear(GL_COLOR_BUFFER_BIT);
glfwSwapBuffers(window);
}
glfwTerminate();
return 0;
}
glClearColor, like all OpenGL functions, works on the current OpenGL context.
You're not setting your window's context as current for your calling thread, so your call to glClearColor does nothing here. Add:
glfwMakeContextCurrent(window);
before your loop.
From glfwMakeContextCurrent docs:
This function makes the OpenGL or OpenGL ES context of the specified window current on the calling thread. A context can only be made current on a single thread at a time and each thread can have only a single current context at a time.
For those of you crazy enough to use pure WIN32 programming:
If your PIXELFORMATDESCRIPTOR has the flag:
PFD_DOUBLEBUFFER
Then all draw calls target the back buffer.
You need to use the windows GDI32 call "SwapBuffers( HDC )" to show the results of your OpenGL calls.
wlgMakeCurrent()
glClearColor( R, G, B, 1.0 ); //: <--Make sure alpha isn't transparent.
glClear( GL_COLOR_BUFFER_BIT )
SwapBuffers( your_window_HDC ); //: from GDI32.dll
To get access to SwapBuffers I use LoadLibrary and GetProcAddress and
put the function pointer in my Win32 functions library.
Also notworthy:
Call SwapBuffers on the same thread as your OpenGL calls.
One more thing. I used multiple threads. So this might be helpful to know:
My window was created in thread "B"
My Context was created in thread "A" using HDC from thread "B"
My openGL draw calls are in thread "A".
I mention this because before I found out about SwapBuffers I thought the problem was because of my multi threading. OpenGL wasn't giving me any errors though, so I had to guess around and experiment and read.