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OpenGL mutiscreens OpenGL in windows

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Hello, at present I’m using Linux to drive 4 screens running OpenGL (Mesa) code. In Linux this is not to hard (in theory), I just tell the code what screen number I’m writing to, then load the graphics, then double buffer that screen. As each screen is give a number by x-windows. However I’ve been asked to change the code to run under windows, unfortunately I’m not a windows programmer. Can anyone advise where to start with double buffering a certain screen and how to set the context? Basically I would like to know how to 1. Set up multiple screens under windows (basically 4 full screen windows) 2a. Then how to set OpenGL to address the correct window 2b. Then how to double buffer only the screen I’m writing to. Thanks, I hope that make sense to someone.

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Quote:
Original post by yoda67
1. Set up multiple screens under windows (basically 4 full screen windows)
2a. Then how to set OpenGL to address the correct window
2b. Then how to double buffer only the screen I’m writing to.

Thanks, I hope that make sense to someone.


Just to get you started, here is a very ugly hackish way to go about that.


/*
* This Code Was Created By Jeff Molofee 2000
* A HUGE Thanks To Fredric Echols For Cleaning Up
* And Optimizing The Base Code, Making It More Flexible!
* If You've Found This Code Useful, Please Let Me Know.
* Visit My Site At nehe.gamedev.net
*/


#include <windows.h> // Header File For Windows
#include <gl\gl.h> // Header File For The OpenGL32 Library
#include <gl\glu.h> // Header File For The GLu32 Library
#include <gl\glaux.h> // Header File For The Glaux Library

bool keys[256]; // Array Used For The Keyboard Routine

struct OpenGLWindow
{
char* classname;
bool active;
bool fullscreen;
HDC hDC;
HGLRC hRC;
HWND hWnd;
HINSTANCE hInstance;
BOOL done;

OpenGLWindow()
{
active = true;
fullscreen = false;
hDC = NULL;
hRC = NULL;
hWnd = NULL;
hInstance = NULL;
BOOL done = false;
}

GLvoid ReSizeGLScene(GLsizei width, GLsizei height) // Resize And Initialize The GL Window
{
if (height==0) // Prevent A Divide By Zero By
{
height=1; // Making Height Equal One
}

glViewport(0,0,width,height); // Reset The Current Viewport

glMatrixMode(GL_PROJECTION); // Select The Projection Matrix
glLoadIdentity(); // Reset The Projection Matrix

// Calculate The Aspect Ratio Of The Window
gluPerspective(45.0f,(GLfloat)width/(GLfloat)height,0.1f,100.0f);

glMatrixMode(GL_MODELVIEW); // Select The Modelview Matrix
glLoadIdentity(); // Reset The Modelview Matrix
}

int InitGL(GLvoid) // All Setup For OpenGL Goes Here
{
glShadeModel(GL_SMOOTH); // Enable Smooth Shading
glClearColor(0.0f, 0.0f, 0.0f, 0.5f); // Black Background
glClearDepth(1.0f); // Depth Buffer Setup
glEnable(GL_DEPTH_TEST); // Enables Depth Testing
glDepthFunc(GL_LEQUAL); // The Type Of Depth Testing To Do
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST); // Really Nice Perspective Calculations
return TRUE; // Initialization Went OK
}

GLvoid KillGLWindow(GLvoid) // Properly Kill The Window
{
if (fullscreen) // Are We In Fullscreen Mode?
{
ChangeDisplaySettings(NULL,0); // If So Switch Back To The Desktop
ShowCursor(TRUE); // Show Mouse Pointer
}

if (hRC) // Do We Have A Rendering Context?
{
if (!wglMakeCurrent(NULL,NULL)) // Are We Able To Release The DC And RC Contexts?
{
MessageBox(NULL,"Release Of DC And RC Failed.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);
}

if (!wglDeleteContext(hRC)) // Are We Able To Delete The RC?
{
MessageBox(NULL,"Release Rendering Context Failed.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);
}
hRC=NULL; // Set RC To NULL
}

if (hDC && !ReleaseDC(hWnd,hDC)) // Are We Able To Release The DC
{
MessageBox(NULL,"Release Device Context Failed.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);
hDC=NULL; // Set DC To NULL
}

if (hWnd && !DestroyWindow(hWnd)) // Are We Able To Destroy The Window?
{
MessageBox(NULL,"Could Not Release hWnd.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);
hWnd=NULL; // Set hWnd To NULL
}

if (!UnregisterClass(classname,hInstance)) // Are We Able To Unregister Class
{
MessageBox(NULL,"Could Not Unregister Class.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);
hInstance=NULL; // Set hInstance To NULL
}
}

/* This Code Creates Our OpenGL Window. Parameters Are: *
* title - Title To Appear At The Top Of The Window *
* width - Width Of The GL Window Or Fullscreen Mode *
* height - Height Of The GL Window Or Fullscreen Mode *
* bits - Number Of Bits To Use For Color (8/16/24/32) *
* fullscreenflag - Use Fullscreen Mode (TRUE) Or Windowed Mode (FALSE) */


BOOL CreateGLWindow(char* className, char* title, int width, int height, int bits, bool fullscreenflag, WNDPROC WndProc)
{
classname = className;
GLuint PixelFormat; // Holds The Results After Searching For A Match
WNDCLASS wc; // Windows Class Structure
DWORD dwExStyle; // Window Extended Style
DWORD dwStyle; // Window Style
RECT WindowRect; // Grabs Rectangle Upper Left / Lower Right Values
WindowRect.left=(long)0; // Set Left Value To 0
WindowRect.right=(long)width; // Set Right Value To Requested Width
WindowRect.top=(long)0; // Set Top Value To 0
WindowRect.bottom=(long)height; // Set Bottom Value To Requested Height

fullscreen = fullscreenflag; // Set The Global Fullscreen Flag

hInstance = GetModuleHandle(NULL); // Grab An Instance For Our Window
wc.style = CS_HREDRAW | CS_VREDRAW | CS_OWNDC; // Redraw On Size, And Own DC For Window.
wc.lpfnWndProc = (WNDPROC) WndProc; // WndProc Handles Messages
wc.cbClsExtra = 0; // No Extra Window Data
wc.cbWndExtra = 0; // No Extra Window Data
wc.hInstance = hInstance; // Set The Instance
wc.hIcon = LoadIcon(NULL, IDI_WINLOGO); // Load The Default Icon
wc.hCursor = LoadCursor(NULL, IDC_ARROW); // Load The Arrow Pointer
wc.hbrBackground = NULL; // No Background Required For GL
wc.lpszMenuName = NULL; // We Don't Want A Menu
wc.lpszClassName = className; // Set The Class Name

if (!RegisterClass(&wc)) // Attempt To Register The Window Class
{
MessageBox(NULL,"Failed To Register The Window Class.","ERROR",MB_OK|MB_ICONEXCLAMATION);
return FALSE; // Return FALSE
}

if (fullscreen) // Attempt Fullscreen Mode?
{
DEVMODE dmScreenSettings; // Device Mode
memset(&dmScreenSettings,0,sizeof(dmScreenSettings)); // Makes Sure Memory's Cleared
dmScreenSettings.dmSize=sizeof(dmScreenSettings); // Size Of The Devmode Structure
dmScreenSettings.dmPelsWidth = width; // Selected Screen Width
dmScreenSettings.dmPelsHeight = height; // Selected Screen Height
dmScreenSettings.dmBitsPerPel = bits; // Selected Bits Per Pixel
dmScreenSettings.dmFields=DM_BITSPERPEL|DM_PELSWIDTH|DM_PELSHEIGHT;

// Try To Set Selected Mode And Get Results. NOTE: CDS_FULLSCREEN Gets Rid Of Start Bar.
if (ChangeDisplaySettings(&dmScreenSettings,CDS_FULLSCREEN)!=DISP_CHANGE_SUCCESSFUL)
{
// If The Mode Fails, Offer Two Options. Quit Or Use Windowed Mode.
if (MessageBox(NULL,"The Requested Fullscreen Mode Is Not Supported By\nYour Video Card. Use Windowed Mode Instead?","NeHe GL",MB_YESNO|MB_ICONEXCLAMATION)==IDYES)
{
fullscreen=FALSE; // Windowed Mode Selected. Fullscreen = FALSE
}
else
{
// Pop Up A Message Box Letting User Know The Program Is Closing.
MessageBox(NULL,"Program Will Now Close.","ERROR",MB_OK|MB_ICONSTOP);
return FALSE; // Return FALSE
}
}
}

if (fullscreen) // Are We Still In Fullscreen Mode?
{
dwExStyle=WS_EX_APPWINDOW; // Window Extended Style
dwStyle=WS_POPUP; // Windows Style
ShowCursor(FALSE); // Hide Mouse Pointer
}
else
{
dwExStyle=WS_EX_APPWINDOW | WS_EX_WINDOWEDGE; // Window Extended Style
dwStyle=WS_OVERLAPPEDWINDOW; // Windows Style
}

AdjustWindowRectEx(&WindowRect, dwStyle, FALSE, dwExStyle); // Adjust Window To True Requested Size

// Create The Window
if (!(hWnd=CreateWindowEx( dwExStyle, // Extended Style For The Window
classname, // Class Name
title, // Window Title
dwStyle | // Defined Window Style
WS_CLIPSIBLINGS | // Required Window Style
WS_CLIPCHILDREN, // Required Window Style
0, 0, // Window Position
WindowRect.right-WindowRect.left, // Calculate Window Width
WindowRect.bottom-WindowRect.top, // Calculate Window Height
NULL, // No Parent Window
NULL, // No Menu
hInstance, // Instance
NULL))) // Dont Pass Anything To WM_CREATE
{
KillGLWindow(); // Reset The Display
MessageBox(NULL,"Window Creation Error.","ERROR",MB_OK|MB_ICONEXCLAMATION);
return FALSE; // Return FALSE
}

static PIXELFORMATDESCRIPTOR pfd= // pfd Tells Windows How We Want Things To Be
{
sizeof(PIXELFORMATDESCRIPTOR), // Size Of This Pixel Format Descriptor
1, // Version Number
PFD_DRAW_TO_WINDOW | // Format Must Support Window
PFD_SUPPORT_OPENGL | // Format Must Support OpenGL
PFD_DOUBLEBUFFER, // Must Support Double Buffering
PFD_TYPE_RGBA, // Request An RGBA Format
bits, // Select Our Color Depth
0, 0, 0, 0, 0, 0, // Color Bits Ignored
0, // No Alpha Buffer
0, // Shift Bit Ignored
0, // No Accumulation Buffer
0, 0, 0, 0, // Accumulation Bits Ignored
16, // 16Bit Z-Buffer (Depth Buffer)
0, // No Stencil Buffer
0, // No Auxiliary Buffer
PFD_MAIN_PLANE, // Main Drawing Layer
0, // Reserved
0, 0, 0 // Layer Masks Ignored
};

if (!(hDC=GetDC(hWnd))) // Did We Get A Device Context?
{
KillGLWindow(); // Reset The Display
MessageBox(NULL,"Can't Create A GL Device Context.","ERROR",MB_OK|MB_ICONEXCLAMATION);
return FALSE; // Return FALSE
}

if (!(PixelFormat=ChoosePixelFormat(hDC,&pfd))) // Did Windows Find A Matching Pixel Format?
{
KillGLWindow(); // Reset The Display
MessageBox(NULL,"Can't Find A Suitable PixelFormat.","ERROR",MB_OK|MB_ICONEXCLAMATION);
return FALSE; // Return FALSE
}

if(!SetPixelFormat(hDC,PixelFormat,&pfd)) // Are We Able To Set The Pixel Format?
{
KillGLWindow(); // Reset The Display
MessageBox(NULL,"Can't Set The PixelFormat.","ERROR",MB_OK|MB_ICONEXCLAMATION);
return FALSE; // Return FALSE
}

if (!(hRC=wglCreateContext(hDC))) // Are We Able To Get A Rendering Context?
{
KillGLWindow(); // Reset The Display
MessageBox(NULL,"Can't Create A GL Rendering Context.","ERROR",MB_OK|MB_ICONEXCLAMATION);
return FALSE; // Return FALSE
}

if(!wglMakeCurrent(hDC,hRC)) // Try To Activate The Rendering Context
{
KillGLWindow(); // Reset The Display
MessageBox(NULL,"Can't Activate The GL Rendering Context.","ERROR",MB_OK|MB_ICONEXCLAMATION);
return FALSE; // Return FALSE
}

ShowWindow(hWnd,SW_SHOW); // Show The Window
SetForegroundWindow(hWnd); // Slightly Higher Priority
SetFocus(hWnd); // Sets Keyboard Focus To The Window
ReSizeGLScene(width, height); // Set Up Our Perspective GL Screen

if (!InitGL()) // Initialize Our Newly Created GL Window
{
KillGLWindow(); // Reset The Display
MessageBox(NULL,"Initialization Failed.","ERROR",MB_OK|MB_ICONEXCLAMATION);
return FALSE; // Return FALSE
}

return TRUE; // Success
}

bool Run()
{
wglMakeCurrent(hDC,hRC);

// Draw The Scene. Watch For ESC Key And Quit Messages From DrawGLScene()
if ((active && !DrawGLScene()) || keys[VK_ESCAPE]) // Active? Was There A Quit Received?
{
done = TRUE; // ESC or DrawGLScene Signalled A Quit
return true;
}
else // Not Time To Quit, Update Screen
{
SwapBuffers(hDC); // Swap Buffers (Double Buffering)
}
return false;
}

int DrawGLScene(GLvoid) // Here's Where We Do All The Drawing
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear Screen And Depth Buffer
glLoadIdentity(); // Reset The Current Modelview Matrix
glTranslatef(-1.5f,0.0f,-6.0f); // Move Left 1.5 Units And Into The Screen 6.0
glBegin(GL_TRIANGLES); // Drawing Using Triangles
glVertex3f( 0.0f, 1.0f, 0.0f); // Top
glVertex3f(-1.0f,-1.0f, 0.0f); // Bottom Left
glVertex3f( 1.0f,-1.0f, 0.0f); // Bottom Right
glEnd(); // Finished Drawing The Triangle
glTranslatef(3.0f,0.0f,0.0f); // Move Right 3 Units
glBegin(GL_QUADS); // Draw A Quad
glVertex3f(-1.0f, 1.0f, 0.0f); // Top Left
glVertex3f( 1.0f, 1.0f, 0.0f); // Top Right
glVertex3f( 1.0f,-1.0f, 0.0f); // Bottom Right
glVertex3f(-1.0f,-1.0f, 0.0f); // Bottom Left
glEnd(); // Done Drawing The Quad
return TRUE; // Keep Going
}
};

#pragma comment(lib, "opengl32.lib")
#pragma comment(lib, "glu32.lib")

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM); // Declaration For WndProc

LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
switch (uMsg) // Check For Windows Messages
{
case WM_ACTIVATE: // Watch For Window Activate Message
{
if (!HIWORD(wParam)) // Check Minimization State
{
//active=TRUE; // Program Is Active
}
else
{
//active=FALSE; // Program Is No Longer Active
}

return 0; // Return To The Message Loop
}

case WM_SYSCOMMAND:
{
switch (wParam)
{
case SC_SCREENSAVE:
case SC_MONITORPOWER:
return 0;
}
break;
}

case WM_CLOSE: // Did We Receive A Close Message?
{
PostQuitMessage(0); // Send A Quit Message
return 0; // Jump Back
}

case WM_KEYDOWN: // Is A Key Being Held Down?
{
keys[wParam] = TRUE; // If So, Mark It As TRUE
return 0; // Jump Back
}

case WM_KEYUP: // Has A Key Been Released?
{
keys[wParam] = FALSE; // If So, Mark It As FALSE
return 0; // Jump Back
}

case WM_SIZE: // Resize The OpenGL Window
{
//ReSizeGLScene(LOWORD(lParam),HIWORD(lParam)); // LoWord=Width, HiWord=Height
return 0; // Jump Back
}
}

// Pass All Unhandled Messages To DefWindowProc
return DefWindowProc(hWnd,uMsg,wParam,lParam);
}

/*int WINAPI WinMain( HINSTANCE hInstance, // Instance
HINSTANCE hPrevInstance, // Previous Instance
LPSTR lpCmdLine, // Command Line Parameters
int nCmdShow) // Window Show State*/


OpenGLWindow gl1, gl2;

int main(int argc, char* argv[])
{
MSG msg; // Windows Message Structure

// Ask The User Which Screen Mode They Prefer
//if (MessageBox(NULL,"Would You Like To Run In Fullscreen Mode?", "Start FullScreen?",MB_YESNO|MB_ICONQUESTION)==IDNO)
{
//fullscreen=FALSE; // Windowed Mode
}

// Create Our OpenGL Window
if (!gl1.CreateGLWindow("og1", "NeHe's First Polygon Tutorial",320,240,16,false,WndProc ))
{
return 0; // Quit If Window Was Not Created
}

if (!gl2.CreateGLWindow("og2", "NeHe's First Polygon Tutorial",320,240,16,false,WndProc ))
{
return 0; // Quit If Window Was Not Created
}

int done = 0;
while(!done) // Loop That Runs While done=FALSE
{
if (PeekMessage(&msg,NULL,0,0,PM_REMOVE)) // Is There A Message Waiting?
{
if (msg.message==WM_QUIT) // Have We Received A Quit Message?
{
done=TRUE; // If So done=TRUE
}
else // If Not, Deal With Window Messages
{
TranslateMessage(&msg); // Translate The Message
DispatchMessage(&msg); // Dispatch The Message
}
}
else // If There Are No Messages
{
done += gl1.Run();
done += gl2.Run();
}
}

// Shutdown
gl1.KillGLWindow(); // Kill The Window
return (msg.wParam); // Exit The Program
}




Now for the specifics:
* For each window you want to make, you need to have a HWND, HDC, and a HGLRC.
* When you want to make a specific window active and use it, you will have to call wglMakeCurrent(hDC,hRC);. Ideally you should refer to this page to see how to handle any errors associated with that function.
* The double buffering is setup in the window creation code, so it should be handled when you call the make current function.

That's about all there is to this, this example is just to show a quick and ugly way to do it using windowed OpenGL screens. You will have to make a little nicer system to handle the 4 full screen windows so you can switch between whatever you have to on demand. If I have time tonight and can come up with anything cleaner I'll post it. Good luck!

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Here's a little cleaner version that shows what my last post was talking about.


#include <windows.h>
#include <gl\gl.h>
#include <gl\glu.h>

#pragma comment(lib, "opengl32.lib")
#pragma comment(lib, "glu32.lib")

bool keys[256];

struct OpenGLWindow
{
char* classname;
bool active;
bool fullscreen;
HDC hDC;
HGLRC hRC;
HWND hWnd;
HINSTANCE hInstance;
BOOL done;

// Function pointer so each window can draw a different scene
typedef bool(*DrawFunction)();

OpenGLWindow()
{
active = true;
fullscreen = false;
hDC = NULL;
hRC = NULL;
hWnd = NULL;
hInstance = NULL;
BOOL done = false;
}

// Resize And Initialize The GL Window
GLvoid ReSizeGLScene(GLsizei width, GLsizei height)
{
// Prevent A Divide By Zero
if(height == 0)
height = 1;

// Reset The Current Viewport
glViewport(0, 0, width, height);

// Select The Projection Matrix
glMatrixMode(GL_PROJECTION);

// Reset The Projection Matrix
glLoadIdentity();

// Calculate The Aspect Ratio Of The Window
gluPerspective(45.0f, (GLfloat)width / (GLfloat)height, 0.1f, 100.0f);

// Select The Modelview Matrix
glMatrixMode(GL_MODELVIEW);

// Reset The Modelview Matrix
glLoadIdentity();
}

// All Setup For OpenGL Goes Here
int InitGL(GLvoid)
{
glShadeModel(GL_SMOOTH);
glClearColor(0.0f, 0.0f, 0.0f, 0.5f);
glClearDepth(1.0f);
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LEQUAL);
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
return TRUE;
}

// Properly Kill The Window
GLvoid Destroy(GLvoid)
{
// Are We In Fullscreen Mode?
if(fullscreen)
{
// If So Switch Back To The Desktop
ChangeDisplaySettings(NULL, 0);

// Show Mouse Pointer
ShowCursor(TRUE);
}

// Do We Have A Rendering Context?
if(hRC)
{
// Are We Able To Release The DC And RC Contexts?
if(!wglMakeCurrent(NULL, NULL))
{
MessageBox(NULL, "Release Of DC And RC Failed.", "SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);
}

// Are We Able To Delete The RC?
if(!wglDeleteContext(hRC))
{
MessageBox(NULL, "Release Rendering Context Failed.", "SHUTDOWN ERROR", MB_OK | MB_ICONINFORMATION);
}

// Set RC To NULL
hRC = NULL;
}

// Are We Able To Release The DC
if(hDC && !ReleaseDC(hWnd, hDC))
{
MessageBox(NULL, "Release Device Context Failed.", "SHUTDOWN ERROR", MB_OK | MB_ICONINFORMATION);
hDC = NULL;
}

// Are We Able To Destroy The Window?
if (hWnd && !DestroyWindow(hWnd))
{
MessageBox(NULL, "Could Not Release hWnd.", "SHUTDOWN ERROR", MB_OK | MB_ICONINFORMATION);
hWnd = NULL;
}

// Are We Able To Unregister Class
if (!UnregisterClass(classname, hInstance))
{
MessageBox(NULL, "Could Not Unregister Class.", "SHUTDOWN ERROR", MB_OK | MB_ICONINFORMATION);
hInstance = NULL;
}
}

BOOL Create(char* className, char* title, int x, int y, int width, int height, int bits, bool fullscreenflag, WNDPROC WndProc)
{
classname = className;
GLuint PixelFormat; // Holds The Results After Searching For A Match
WNDCLASS wc; // Windows Class Structure
DWORD dwExStyle; // Window Extended Style
DWORD dwStyle; // Window Style
RECT WindowRect; // Grabs Rectangle Upper Left / Lower Right Values
WindowRect.left=(long)0; // Set Left Value To 0
WindowRect.right=(long)width; // Set Right Value To Requested Width
WindowRect.top=(long)0; // Set Top Value To 0
WindowRect.bottom=(long)height; // Set Bottom Value To Requested Height

fullscreen = fullscreenflag; // Set The Global Fullscreen Flag

hInstance = GetModuleHandle(NULL); // Grab An Instance For Our Window
wc.style = CS_HREDRAW | CS_VREDRAW | CS_OWNDC; // Redraw On Size, And Own DC For Window.
wc.lpfnWndProc = (WNDPROC) WndProc; // WndProc Handles Messages
wc.cbClsExtra = 0; // No Extra Window Data
wc.cbWndExtra = 0; // No Extra Window Data
wc.hInstance = hInstance; // Set The Instance
wc.hIcon = LoadIcon(NULL, IDI_WINLOGO); // Load The Default Icon
wc.hCursor = LoadCursor(NULL, IDC_ARROW); // Load The Arrow Pointer
wc.hbrBackground = NULL; // No Background Required For GL
wc.lpszMenuName = NULL; // We Don't Want A Menu
wc.lpszClassName = className; // Set The Class Name

if (!RegisterClass(&wc)) // Attempt To Register The Window Class
{
MessageBox(NULL,"Failed To Register The Window Class.","ERROR",MB_OK|MB_ICONEXCLAMATION);
return FALSE; // Return FALSE
}

if (fullscreen) // Attempt Fullscreen Mode?
{
DEVMODE dmScreenSettings; // Device Mode
memset(&dmScreenSettings,0,sizeof(dmScreenSettings)); // Makes Sure Memory's Cleared
dmScreenSettings.dmSize=sizeof(dmScreenSettings); // Size Of The Devmode Structure
dmScreenSettings.dmPelsWidth = width; // Selected Screen Width
dmScreenSettings.dmPelsHeight = height; // Selected Screen Height
dmScreenSettings.dmBitsPerPel = bits; // Selected Bits Per Pixel
dmScreenSettings.dmFields=DM_BITSPERPEL|DM_PELSWIDTH|DM_PELSHEIGHT;

// Try To Set Selected Mode And Get Results. NOTE: CDS_FULLSCREEN Gets Rid Of Start Bar.
if (ChangeDisplaySettings(&dmScreenSettings,CDS_FULLSCREEN)!=DISP_CHANGE_SUCCESSFUL)
{
// If The Mode Fails, Offer Two Options. Quit Or Use Windowed Mode.
if (MessageBox(NULL,"The Requested Fullscreen Mode Is Not Supported By\nYour Video Card. Use Windowed Mode Instead?","NeHe GL",MB_YESNO|MB_ICONEXCLAMATION)==IDYES)
{
fullscreen=FALSE; // Windowed Mode Selected. Fullscreen = FALSE
}
else
{
// Pop Up A Message Box Letting User Know The Program Is Closing.
MessageBox(NULL,"Program Will Now Close.","ERROR",MB_OK|MB_ICONSTOP);
return FALSE; // Return FALSE
}
}
}

if (fullscreen) // Are We Still In Fullscreen Mode?
{
dwExStyle=WS_EX_APPWINDOW; // Window Extended Style
dwStyle=WS_POPUP; // Windows Style
ShowCursor(FALSE); // Hide Mouse Pointer
}
else
{
dwExStyle=WS_EX_APPWINDOW | WS_EX_WINDOWEDGE; // Window Extended Style
dwStyle=WS_OVERLAPPEDWINDOW; // Windows Style
}

AdjustWindowRectEx(&WindowRect, dwStyle, FALSE, dwExStyle); // Adjust Window To True Requested Size

// Create The Window
if (!(hWnd=CreateWindowEx( dwExStyle, // Extended Style For The Window
classname, // Class Name
title, // Window Title
dwStyle | // Defined Window Style
WS_CLIPSIBLINGS | // Required Window Style
WS_CLIPCHILDREN, // Required Window Style
x, y, // Window Position
WindowRect.right-WindowRect.left, // Calculate Window Width
WindowRect.bottom-WindowRect.top, // Calculate Window Height
NULL, // No Parent Window
NULL, // No Menu
hInstance, // Instance
NULL))) // Dont Pass Anything To WM_CREATE
{
Destroy(); // Reset The Display
MessageBox(NULL,"Window Creation Error.","ERROR",MB_OK|MB_ICONEXCLAMATION);
return FALSE; // Return FALSE
}

static PIXELFORMATDESCRIPTOR pfd= // pfd Tells Windows How We Want Things To Be
{
sizeof(PIXELFORMATDESCRIPTOR), // Size Of This Pixel Format Descriptor
1, // Version Number
PFD_DRAW_TO_WINDOW | // Format Must Support Window
PFD_SUPPORT_OPENGL | // Format Must Support OpenGL
PFD_DOUBLEBUFFER, // Must Support Double Buffering
PFD_TYPE_RGBA, // Request An RGBA Format
bits, // Select Our Color Depth
0, 0, 0, 0, 0, 0, // Color Bits Ignored
0, // No Alpha Buffer
0, // Shift Bit Ignored
0, // No Accumulation Buffer
0, 0, 0, 0, // Accumulation Bits Ignored
16, // 16Bit Z-Buffer (Depth Buffer)
0, // No Stencil Buffer
0, // No Auxiliary Buffer
PFD_MAIN_PLANE, // Main Drawing Layer
0, // Reserved
0, 0, 0 // Layer Masks Ignored
};

if (!(hDC=GetDC(hWnd))) // Did We Get A Device Context?
{
Destroy(); // Reset The Display
MessageBox(NULL,"Can't Create A GL Device Context.","ERROR",MB_OK|MB_ICONEXCLAMATION);
return FALSE; // Return FALSE
}

if (!(PixelFormat=ChoosePixelFormat(hDC,&pfd))) // Did Windows Find A Matching Pixel Format?
{
Destroy(); // Reset The Display
MessageBox(NULL,"Can't Find A Suitable PixelFormat.","ERROR",MB_OK|MB_ICONEXCLAMATION);
return FALSE; // Return FALSE
}

if(!SetPixelFormat(hDC,PixelFormat,&pfd)) // Are We Able To Set The Pixel Format?
{
Destroy(); // Reset The Display
MessageBox(NULL,"Can't Set The PixelFormat.","ERROR",MB_OK|MB_ICONEXCLAMATION);
return FALSE; // Return FALSE
}

if (!(hRC=wglCreateContext(hDC))) // Are We Able To Get A Rendering Context?
{
Destroy(); // Reset The Display
MessageBox(NULL,"Can't Create A GL Rendering Context.","ERROR",MB_OK|MB_ICONEXCLAMATION);
return FALSE; // Return FALSE
}

if(!wglMakeCurrent(hDC,hRC)) // Try To Activate The Rendering Context
{
Destroy(); // Reset The Display
MessageBox(NULL,"Can't Activate The GL Rendering Context.","ERROR",MB_OK|MB_ICONEXCLAMATION);
return FALSE; // Return FALSE
}

ShowWindow(hWnd,SW_SHOW); // Show The Window
SetForegroundWindow(hWnd); // Slightly Higher Priority
SetFocus(hWnd); // Sets Keyboard Focus To The Window
ReSizeGLScene(width, height); // Set Up Our Perspective GL Screen

if (!InitGL()) // Initialize Our Newly Created GL Window
{
Destroy(); // Reset The Display
MessageBox(NULL,"Initialization Failed.","ERROR",MB_OK|MB_ICONEXCLAMATION);
return FALSE; // Return FALSE
}

return TRUE; // Success
}

bool Run(DrawFunction drawFunc)
{
wglMakeCurrent(hDC,hRC);

// Draw The Scene. Watch For ESC Key And Quit Messages From DrawGLScene()
if ((active && !(*drawFunc)()) || keys[VK_ESCAPE]) // Active? Was There A Quit Received?
{
done = TRUE; // ESC or DrawGLScene Signalled A Quit
return true;
}
else // Not Time To Quit, Update Screen
{
SwapBuffers(hDC); // Swap Buffers (Double Buffering)
}
return false;
}
};

LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
switch (uMsg) // Check For Windows Messages
{
case WM_CLOSE: // Did We Receive A Close Message?
{
PostQuitMessage(0); // Send A Quit Message
return 0; // Jump Back
}

case WM_KEYDOWN: // Is A Key Being Held Down?
{
keys[wParam] = TRUE; // If So, Mark It As TRUE
return 0; // Jump Back
}

case WM_KEYUP: // Has A Key Been Released?
{
keys[wParam] = FALSE; // If So, Mark It As FALSE
return 0; // Jump Back
}
}

// Pass All Unhandled Messages To DefWindowProc
return DefWindowProc(hWnd,uMsg,wParam,lParam);
}

OpenGLWindow gl1, gl2, gl3, gl4;

bool Draw1()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear Screen And Depth Buffer
glLoadIdentity(); // Reset The Current Modelview Matrix
glTranslatef(-1.5f,0.0f,-6.0f); // Move Left 1.5 Units And Into The Screen 6.0
glBegin(GL_TRIANGLES); // Drawing Using Triangles
glVertex3f( 0.0f, 1.0f, 0.0f); // Top
glVertex3f(-1.0f,-1.0f, 0.0f); // Bottom Left
glVertex3f( 1.0f,-1.0f, 0.0f); // Bottom Right
glEnd(); // Finished Drawing The Triangle
return true;
}

bool Draw2()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear Screen And Depth Buffer
glLoadIdentity(); // Reset The Current Modelview Matrix
glTranslatef(0.0f,0.0f,-6.0f); // Move Right 3 Units
glBegin(GL_QUADS); // Draw A Quad
glVertex3f(-1.0f, 1.0f, 0.0f); // Top Left
glVertex3f( 1.0f, 1.0f, 0.0f); // Top Right
glVertex3f( 1.0f,-1.0f, 0.0f); // Bottom Right
glVertex3f(-1.0f,-1.0f, 0.0f); // Bottom Left
glEnd(); // Done Drawing The Quad
return true;
}

bool Draw3()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear Screen And Depth Buffer
glLoadIdentity(); // Reset The Current Modelview Matrix
glTranslatef(-1.5f,0.0f,-6.0f); // Move Left 1.5 Units And Into The Screen 6.0
glBegin(GL_TRIANGLES); // Drawing Using Triangles
glVertex3f( 0.0f, 1.0f, 0.0f); // Top
glVertex3f(-1.0f,-1.0f, 0.0f); // Bottom Left
glVertex3f( 1.0f,-1.0f, 0.0f); // Bottom Right
glEnd(); // Finished Drawing The Triangle
glTranslatef(3.0f,0.0f,0.0f); // Move Right 3 Units
glBegin(GL_QUADS); // Draw A Quad
glVertex3f(-1.0f, 1.0f, 0.0f); // Top Left
glVertex3f( 1.0f, 1.0f, 0.0f); // Top Right
glVertex3f( 1.0f,-1.0f, 0.0f); // Bottom Right
glVertex3f(-1.0f,-1.0f, 0.0f); // Bottom Left
glEnd(); // Done Drawing The Quad
return true;
}

bool Draw4()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear Screen And Depth Buffer
glLoadIdentity(); // Reset The Current Modelview Matrix
glTranslatef(-1.5f,0.0f,-6.0f); // Move Left 1.5 Units And Into The Screen 6.0
glColor3f(1, 0, 0);
glBegin(GL_TRIANGLES); // Drawing Using Triangles
glVertex3f( 0.0f, 1.0f, 0.0f); // Top
glVertex3f(-1.0f,-1.0f, 0.0f); // Bottom Left
glVertex3f( 1.0f,-1.0f, 0.0f); // Bottom Right
glEnd(); // Finished Drawing The Triangle
glColor3f(1, 0, 1);
glTranslatef(3.0f,0.0f,0.0f); // Move Right 3 Units
glBegin(GL_QUADS); // Draw A Quad
glVertex3f(-1.0f, 1.0f, 0.0f); // Top Left
glVertex3f( 1.0f, 1.0f, 0.0f); // Top Right
glVertex3f( 1.0f,-1.0f, 0.0f); // Bottom Right
glVertex3f(-1.0f,-1.0f, 0.0f); // Bottom Left
glEnd(); // Done Drawing The Quad
return true;
}

int main(int argc, char* argv[])
{
// Create Our 4 OpenGL Windows
if (!gl1.Create("og1", "Window 1", 0, 0, 320, 240, 16, false, WndProc ))
return 0;
if (!gl2.Create("og2", "Window 2", 320, 0, 320, 240, 16, false, WndProc ))
return 0;
if (!gl3.Create("og3", "Window 3", 0, 240, 320, 240, 16, false, WndProc ))
return 0;
if (!gl4.Create("og4", "Window 4", 320, 240, 320, 240, 16, false, WndProc ))
return 0;

int done = 0;
MSG msg;
while(!done)
{
// Is There A Message Waiting?
if(PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
{
// Have We Received A Quit Message?
if(msg.message == WM_QUIT)
{
done = true;
}

// If Not, Deal With Window Messages
else
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}

// If There Are No Messages
else
{
// Run all windows with the respective draw functions
done += gl1.Run(Draw1);
done += gl2.Run(Draw2);
done += gl3.Run(Draw3);
done += gl4.Run(Draw4);
}
}

// Shutdown, only need to call 1, *I think*
gl1.Destroy();

return 0;
}



You can extend it the same way and allow each window to have a function pointer for the initialize functions, draw, and update as well as anything else you need. That way, you can use just one class andn to have to worry about inheritance or the like. Here's a screenshot of the results of this example:

Image Hosted by ImageShack.us

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wouldn't it be proper to query how many display devices are there and make a context for each? And then, somehow, render a specific viewport of the scene on each?

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Hello,

You will need to get information about the available monitors on the system. Here's some code of mine I wrote recently (meaning it hasn't been tested much) that you can use as a base for enumerating monitors.

EnumerateDisplays.h

struct DisplayMode
{
DisplayMode() : width(-1), height(-1), refreshRate(-1), bpp(-1) {}
DisplayMode(int w, int h, int r, int BPP) : width(w), height(h), refreshRate(r), bpp(BPP) {}

int width;
int height;
int refreshRate;
int bpp;
};

// Class: Display
//
// A physical display on a computer.
class Display
{
public:
Display();
Display(int index, int x, int y, bool primary, string devName, string devString,
const vector<DisplayMode>& displayModes);

//bool Defaulted() const { return m_Index == -1; }

// Function: GetName
//
// Retrieves the name of the display.
string GetName() const;

// Function: GetDisplayModes
//
// Retrieves a vector of available <DisplayModes> for the display.
const vector<DisplayMode>& GetDisplayModes() const;

// Function: SelectDisplayMode
//
// Selects the display mode to set this monitor to when a window is
void SelectDisplayMode(DisplayMode mode);
private:
int m_Index;
int m_XOffset, m_YOffset;
bool m_PrimaryDisplay;
string m_DeviceName, m_DeviceString;

vector<DisplayMode> m_DisplayModes;
DisplayMode m_SelectedDisplayMode;
};

// Function: EnumerateDisplays
//
// Enumerates all displays available.
//
// Returns:
// The vector of <Displays> filled with the list of displays.
vector<Display>& EnumerateDisplays();



EnumerateDisplays.cpp

Display::Display()
: m_Index(-1),
m_XOffset(-1),
m_YOffset(-1),
m_PrimaryDisplay(false),
m_DeviceName(cs("UNKNOWN")),
m_DeviceString(cs("UNKNOWN"))
{
}

Display::Display(int index, int x, int y, bool primary, string devName, string devString,
const vector<DisplayMode>& displayModes)
: m_Index(index),
m_XOffset(x),
m_YOffset(y),
m_PrimaryDisplay(primary),
m_DeviceName(devName),
m_DeviceString(devString),
m_DisplayModes(displayModes)
{
}

string Display::GetName() const
{
return m_DeviceString;
}

const vector<DisplayMode>& Display::GetDisplayModes() const
{
return m_DisplayModes;
}

void Display::SelectDisplayMode(DisplayMode mode)
{
m_SelectedDisplayMode = mode;
}

BOOL CALLBACK MonitorEnumProc(HMONITOR hMonitor, HDC hdcMonitor, LPRECT lprcMonitor, LPARAM dwData)
{
MONITORINFOEX monInfo;
monInfo.cbSize = sizeof(MONITORINFOEX);
GetMonitorInfo(hMonitor, &monInfo);

vector<Display>& displays = *((vector<Display>*)dwData);

int ddIndex = 0;
bool primaryDisplay = false;
string deviceName = string(monInfo.szDevice), deviceString;
vector<DisplayMode> displayModes;

DISPLAY_DEVICE displayDevice;
displayDevice.cb = sizeof(DISPLAY_DEVICE);

for (ddIndex = 0; EnumDisplayDevices(0, ddIndex, &displayDevice, 0); ddIndex++)
{
if ((string(displayDevice.DeviceName) == deviceName) &&
!((bool)(DISPLAY_DEVICE_MIRRORING_DRIVER & displayDevice.StateFlags)) &&
!((bool)(DISPLAY_DEVICE_REMOVABLE & displayDevice.StateFlags)))
{
deviceString = string(displayDevice.DeviceString);
primaryDisplay = (bool)(DISPLAY_DEVICE_PRIMARY_DEVICE & displayDevice.StateFlags);

DEVMODE devMode;
devMode.dmSize = sizeof(DEVMODE);
for (int j = 0; EnumDisplaySettingsEx(displayDevice.DeviceName, j, &devMode, 0); j++)
{
if (devMode.dmPelsWidth < 640 || devMode.dmPelsHeight < 480 || devMode.dmBitsPerPel < 16)
continue;

POINTL position;
position.x = monInfo.rcMonitor.left;
position.y = monInfo.rcMonitor.top;
devMode.dmPosition = position;

devMode.dmFields = DM_BITSPERPEL | DM_PELSWIDTH | DM_PELSHEIGHT |
DM_DISPLAYFREQUENCY | DM_POSITION;
LONG result = ChangeDisplaySettingsEx(displayDevice.DeviceName, &devMode, 0,
CDS_TEST, 0);
if (result != DISP_CHANGE_SUCCESSFUL)
continue;

displayModes.push_back(DisplayMode(devMode.dmPelsWidth, devMode.dmPelsHeight,
devMode.dmDisplayFrequency, devMode.dmBitsPerPel));
}

break;
}
}

displays.push_back(Display(ddIndex, monInfo.rcMonitor.left, monInfo.rcMonitor.top,
primaryDisplay, deviceName, deviceString, displayModes));

return TRUE;
}

vector<Display>& sl::EnumerateDisplays()
{
static vector<Display> s_Displays;

if (s_Displays.empty())
{
if (!EnumDisplayMonitors(0, 0, MonitorEnumProc, (LPARAM)&s_Displays))
THROW_EXCEPTION("Could not enumerate available display devices");
}

return s_Displays;
}



I haven't commented much in the above code. If you have any questions, just ask. If you look up the functions on MSDN (EnumDisplayMonitors MONITORINFOEX GetMonitorInfo DISPLAY_DEVICE EnumDisplayDevices EnumDisplaySettingsEx ChangeDisplaySettingsEx) you should get some good information.

With that code, you should be able to create multiple windows that each span an entire monitor in fullscreen mode (this is what you need to do, isn't it?). It's simply a matter of creating the windows at the right position and the right size to match the monitor.

This is unfortunately all I can help with for now due to lack of time. Setting up GL to address multiple windows shouldn't be too hard. It's just a matter of activating the correct rendering context.

Slaru

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Ohh, was the OP asking how to get multiple OpenGL windows, or how to use OpenGL across multiple monitors. I read it as the former, but maybe yoda67 can clarify some more.

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