3.Adding Color

  1 #include <windows.h>
  2 #include <gl/glew.h>
  3 #include <gl/glut.h>
  4 
  5 /*
  6  *  Every OpenGL program is linked to a Rendering Context.
  7  *  A Rendering Context is what links OpenGL calls to the Device Context.
  8  *  In order for your program to draw to a Window you need to create a Device Context.
  9  *  The DC connects the Window to the GDI (Graphics Device Interface).
 10  */
 11 
 12 HGLRC     hRC = NULL;         // Permanent rendering context
 13 HDC       hDC = NULL;         // Private GDI device context
 14 HWND      hWnd = NULL;        // Holds our window handle
 15 HINSTANCE hInstance;          // Holds the instance of the application
 16 
 17 /*
 18  *  It‘s important to make this global so that each procedure knows if 
 19  *  the program is running in fullscreen mode or not.
 20  */
 21 
 22 bool keys[256];         // Array used for the keyboard routine
 23 bool active = TRUE;     // Window active flag set to TRUE by default
 24 bool fullscreen = TRUE; // Fullscreen flag set to fullscreen mode by default
 25 
 26 /*
 27  *  CreateGLWindow() has a reference to WndProc() but WndProc() comes after CreateGLWindow().
 28  */
 29 
 30 LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM); // Declaration for WndProc
 31 
 32 /*
 33  *  The job of the next section of code is to resize the OpenGL scene 
 34  *  whenever the window (assuming you are using a Window rather than fullscreen mode) has been resized.
 35  */
 36 
 37 GLvoid ReSizeGLScene(GLsizei width, GLsizei height)   // Resize and initialize the GL window
 38 {
 39     if (height == 0) {                                // Prevent a divide by zero by
 40         height = 1;                                   // Making height equal one
 41     }
 42     
 43     glViewport(0, 0, width, height);                  // Reset the current viewport
 44 
 45     /*
 46      *  The following lines set the screen up for a perspective view. 
 47      *  Meaning things in the distance get smaller. This creates a realistic looking scene. 
 48      *  The perspective is calculated with a 45 degree viewing angle based on 
 49      *  the windows width and height. The 0.1f, 100.0f is the starting point and 
 50      *  ending point for how deep we can draw into the screen.
 51      *
 52      *  The projection matrix is responsible for adding perspective to our scene.
 53      *  glLoadIdentity() restores the selected matrix to it‘s original state.
 54      *  The modelview matrix is where our object information is stored.
 55      *   Lastly we reset the modelview matrix.
 56      */
 57 
 58     glMatrixMode(GL_PROJECTION);                      // Select the projection matrix
 59     glLoadIdentity();                                 // Reset the projection matrix
 60     
 61                                                       // Calculate the aspect ratio of the window
 62     gluPerspective(45.0f, (GLfloat)width / (GLfloat)height, 0.1f, 100.0f);
 63 
 64     glMatrixMode(GL_MODELVIEW);                       // Seclet the modelview matrix
 65     glLoadIdentity();                                 // Reset the modelview matrix
 66 }
 67 
 68 int InitGL(GLvoid)                                    // All setup for OpenGL goes here
 69 {
 70     /*
 71      *  Smooth shading blends colors nicely across a polygon, and smoothes out lighting.
 72      */
 73     
 74     glShadeModel(GL_SMOOTH);                          // Enables smooth shading
 75 
 76     glClearColor(0.0f, 0.0f, 0.0f, 0.0f);             // Black background
 77 
 78     /*
 79      *  Think of the depth buffer as layers into the screen. 
 80      *  The depth buffer keeps track of how deep objects are into the screen.
 81      */
 82 
 83     glClearDepth(1.0f);                               // Depth buffer setup
 84     glEnable(GL_DEPTH_TEST);                          // Enable depth testing
 85     glDepthFunc(GL_LEQUAL);                           // The typr of depth test to do
 86 
 87     /*
 88      *  Next we tell OpenGL we want the best perspective correction to be done. 
 89      *  This causes a very tiny performance hit, but makes the perspective view look a bit better.
 90      */
 91 
 92     glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);   // Really nice perspective calculations
 93 
 94     return TRUE;
 95 }
 96 
 97 /*
 98  *  For now all we will do is clear the screen to the color we previously decided on, 
 99  *  clear the depth buffer and reset the scene. We wont draw anything yet.
100  */
101 /******************************************************************************************************************************************/
102 /******************************************************************************************************************************************/
103 int DrawGLScene(GLvoid)                                  // Here‘s where we do all the drawing
104 {
105     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);  // Clear the screen and the depth buffer
106     glLoadIdentity();                                    // Reset the current modelview matrix
107     
108     /*
109      *  When you do a glLoadIdentity() what you are doing is moving back to 
110      *  the center of the screen with the X axis(轴) running left to right, 
111      *  the Y axis moving up and down, and the Z axis moving into, and out of the screen.
112      */
113     /*
114      *  glTranslatef(x, y, z) moves along the X, Y and Z axis, in that order.
115      *  When you translate, you are not moving a set amount(数量) from the center of the screen, 
116      *  you are moving a set amount from wherever you currently were on the screen.
117      */
118     glTranslatef(-1.5f, 0.0f, -6.0f);                    // Move left 1.5 units and into the screen 6.0
119     glBegin(GL_TRIANGLES);                               // Drawing using traingles
120         glColor3f(1.0, 0.0, 0.0);                        // Set the color to red
121         glVertex3f(0.0f, 1.0f, 0.0f);                    // Top
122         glColor3f(0.0, 1.0, 0.0);                        // Set the color to green
123         glVertex3f(-1.0f, -1.0f, 0.0f);                  // Bottom left
124         glColor3f(0.0, 0.0, 1.0);                        // Set the color to blue
125         glVertex3f(1.0f, -1.0f, 0.0f);                   // Bottom right
126     glEnd();                                             // Finished drawing the traingles
127 
128     glTranslatef(3.0f, 0.0f, 0.0f);                      // Move left 3 units
129     
130     /*
131      *  By drawing in a clockwise order, the square will be drawn as a back face. 
132      *  Meaning the side of the quad we see is actually the back. 
133      *  Objects drawn in a counter clockwise order will be facing us.
134      */
135 
136     glBegin(GL_QUADS);                                   // Draw a quad
137         glColor3f(0.75, 0.0, 0.0);
138         glVertex3f(-1.0f, 1.0f, 0.0f);                   // Top left
139         glColor3f(1.0, 0.5, 0.0);
140         glVertex3f(1.0f, 1.0f, 0.0f);                    // Top right
141         glColor3f(1.0, 1.0, 0.25);
142         glVertex3f(1.0f, -1.0f, 0.0f);                   // Bottom right
143         glColor3f(1.0, 0.0, 1.0);
144         glVertex3f(-1.0f, -1.0f, 0.0f);                  // Bottom left
145     glEnd();                                             // Done drawing the quad
146     return TRUE;                                         // everthing went OK
147 }
148 /******************************************************************************************************************************************/
149 /******************************************************************************************************************************************/
150 /*
151  *  The job of KillGLWindow() is to release the Rendering Context, 
152  *  the Device Context and finally the Window Handle. 
153  */
154 
155 GLvoid KillGLWindow(GLvoid)                              // Properly kill the window
156 {
157     if (fullscreen) {                                    // Are we in fullscreen mode
158         
159         /*
160          *  We use ChangeDisplaySettings(NULL,0) to return us to our original desktop.
161          *  After we‘ve switched back to the desktop we make the cursor visible again.
162          */
163 
164         ChangeDisplaySettings(NULL, 0);                  // if so switch back to the desktop
165         ShowCursor(TRUE);                                // Show mouse pointer
166     }
167 
168     if (hRC) {                                           // Do we have a rendering context
169         if (!wglMakeCurrent(NULL, NULL)) {                // Are we able to release the DC and RC contexts
170             MessageBox(NULL, "Release of DC and RC failed.", "SHUTDOWN ERROR", MB_OK | MB_ICONINFORMATION);
171         }
172 
173         if (!wglDeleteContext(hRC)) {                     // Are we able to delete the RC
174             MessageBox(NULL, "Release rendering context failed.", "SHUTDOWN ERROR", MB_OK | MB_ICONINFORMATION);
175             hRC = NULL;                                  // Set RC to NULL
176         }
177 
178         if (hDC && !ReleaseDC(hWnd, hDC)) {              // Are we able to release the DC
179             MessageBox(NULL, "Release device context failed.", "SHUTDOWN ERROR", MB_OK | MB_ICONINFORMATION);
180             hDC = NULL;                                  // Set DC to NULL
181         }
182         if (hWnd && !DestroyWindow(hWnd)) {              // Are we able to destroy the window
183             MessageBox(NULL, "Could not release hWnd.", "SHUTDOWN ERROR", MB_OK | MB_ICONINFORMATION);
184             hWnd = NULL;                                 // Set hWnd to NULL
185         }
186 
187         if (!UnregisterClass("OpenGL", hInstance)) {     // Are we able to unregister class
188             MessageBox(NULL, "Could not register class.", "SHUTDOWN ERROR", MB_OK | MB_ICONINFORMATION);
189             hInstance = NULL;                            // Set hInstance to NULL
190         }
191     }
192 }
193 
194 /*
195  * The next section of code creates our OpenGL Window.
196  */
197 
198 BOOL CreateGLWindow(char* title, int width, int height, int bits, bool fullscreenflag)
199 {
200     /*
201      * Find  a pixel format that matches the one we want
202      */
203     GLuint PixelFormat;                                  // Holds the result after serching for a match
204     
205     /*
206      * Before you create a window, you MUST register a Class for the window
207      */
208     WNDCLASS wc;                                         // Windows class structure
209 
210     /*
211      *  dwExStyle and dwStyle will store the Extended and normal Window Style Information.
212     */
213     DWORD dwExStyle;                                     // Window extend style
214     DWORD dwStyle;                                       // Window style
215 
216     RECT WindowRect;                                     // Grabs rectangle upper left/lower right values
217     WindowRect.left = (long)0;                           // Set left value to 0
218     WindowRect.right = (long)width;                      // Set right value to requested width
219     WindowRect.top = (long)0;                            // Set top value to 0
220     WindowRect.bottom = (long)height;                    // Set bottom value to requested height
221 
222     fullscreen = fullscreenflag;                         // Set the global fullscreen flag
223 
224     /*
225      *  The style CS_HREDRAW and CS_VREDRAW force the Window to redraw whenever it is resized. 
226      *  CS_OWNDC creates a private DC for the Window. Meaning the DC is not shared across applications. 
227      *  WndProc is the procedure that watches for messages in our program. 
228      *  No extra Window data is used so we zero the two fields. Then we set the instance. 
229      *  Next we set hIcon to NULL meaning we don‘t want an ICON in the Window, 
230      *  and for a mouse pointer we use the standard arrow. The background color doesn‘t matter 
231      *  (we set that in GL). We don‘t want a menu in this Window so we set it to NULL, 
232      *  and the class name can be any name you want. I‘ll use "OpenGL" for simplicity.
233      */
234     hInstance = GetModuleHandle(NULL);                   // Grab an instance for our window
235     wc.style = CS_HREDRAW | CS_VREDRAW | CS_OWNDC;       // Redraw on move, and own DC for window
236     wc.lpfnWndProc = (WNDPROC)WndProc;                   // WndProc handles message
237     wc.cbClsExtra = 0;                                   // No extra window date
238     wc.cbWndExtra = 0;                                   // No extra window date
239     wc.hInstance = hInstance;                            // set the instance
240     wc.hIcon = LoadIcon(NULL, IDI_WINLOGO);              // Load the default icon
241     wc.hCursor = LoadCursor(NULL, IDC_ARROW);            // Load the arrow pointer
242     wc.hbrBackground = NULL;                             // No background requried for GL
243     wc.lpszMenuName = NULL;                              // We don‘t want a menu
244     wc.lpszClassName = "OpenGL";                         // set the class name
245 
246     if (!RegisterClass(&wc)) {                           // Attempt to register the window class
247         MessageBox(NULL, "Failed to register the window class.", "ERROR", MB_OK | MB_ICONEXCLAMATION);
248         return FALSE;                                    // Exit and return false
249     }
250 
251     if (fullscreen) {                                    // attempt fullsreen model
252         
253         /*
254         T*  here are a few very important things you should keep in mind when switching to full screen mode.
255          *  Make sure the width and height that you use in fullscreen mode is the same as 
256          *  the width and height you plan to use for your window, and most importantly,
257          *  set fullscreen mode BEFORE you create your window.
258          */
259         DEVMODE dmScreenSettings;                        // Device mode
260         memset(&dmScreenSettings, 0, sizeof(dmScreenSettings)); // Make sure memory‘s cleared
261         dmScreenSettings.dmSize = sizeof(dmScreenSettings);     // Size of devmode structure
262         dmScreenSettings.dmPelsWidth = width;            // Select window width
263         dmScreenSettings.dmPelsHeight = height;          // Select window height
264         dmScreenSettings.dmBitsPerPel = bits;            // Select bits per pixel
265         dmScreenSettings.dmFields = DM_BITSPERPEL | DM_PELSWIDTH | DM_PELSHEIGHT;
266         
267         /*
268          *  In the line below ChangeDisplaySettings tries to switch to a mode that matches 
269          *  what we stored in dmScreenSettings. I use the parameter CDS_FULLSCREEN when switching modes, 
270          *  because it‘s supposed to remove the start bar at the bottom of the screen, 
271          *  plus it doesn‘t move or resize the windows on your desktop when you switch to 
272          *  fullscreen mode and back.
273          */
274         //Try to set selected mode and get results. Note: CDS_FULLSCREEN gets rid of start bar
275         if (ChangeDisplaySettings(&dmScreenSettings, CDS_FULLSCREEN) != DISP_CHANGE_SUCCESSFUL) {
276             //If the mode fails, offer two options. Quit or run in a window
277             if (MessageBox(NULL, "The requested fullscreen mode is not supported by\n your video card. Use"
278                 "windowed mode instead?", "GL", MB_YESNO | MB_ICONEXCLAMATION) == IDYES)
279             {
280                 fullscreen = FALSE;                       // Select windowed mode (fullscreen=FLASE)
281             }
282             else {
283                 // Pop up a message box letting user know the programe is closing.
284                 MessageBox(NULL, "Program will now close.", "ERROR", MB_OK | MB_ICONSTOP);
285                 return FALSE;                             // Exit and return FALSE
286             }
287         }
288     }
289 
290     if (fullscreen) {                                     // Are we still in fullscreen mode
291         
292         /*
293          *  If we are still in fullscreen mode we‘ll set the extended style to WS_EX_APPWINDOW, 
294          *  which force a top level window down to the taskbar once our window is visible. 
295          *  For the window style we‘ll create a WS_POPUP window. 
296          *  This type of window has no border around it, making it perfect for fullscreen mode.
297 
298          *  Finally, we disable the mouse pointer. If your program is not interactive, 
299          *  it‘s usually nice to disable the mouse pointer when in fullscreen mode. It‘s up to you though.
300          */
301         dwExStyle = WS_EX_APPWINDOW;                      // Window extended style
302         dwStyle = WS_POPUP;                               // Window style
303         ShowCursor(FALSE);                                // Hide mosue pointer 
304     }
305     else {
306 
307         /*
308          *  If we‘re using a window instead of fullscreen mode, 
309          *  we‘ll add WS_EX_WINDOWEDGE to the extended style. This gives the window a more 3D look. 
310          *  For style we‘ll use WS_OVERLAPPEDWINDOW instead of WS_POPUP. 
311          *  WS_OVERLAPPEDWINDOW creates a window with a title bar, sizing border, 
312          *  window menu, and minimize / maximize buttons.
313          */
314         dwExStyle = WS_EX_APPWINDOW | WS_EX_WINDOWEDGE;   // Window extended style
315         dwStyle = WS_OVERLAPPEDWINDOW;                    // Window style
316     }
317 
318     /*
319      *  By using the AdjustWindowRectEx command none of our OpenGL scene will be covered up by the borders, 
320      *  instead, the window will be made larger to account for the pixels needed to draw the window border. 
321      *  In fullscreen mode, this command has no effect.
322      */
323     AdjustWindowRectEx(&WindowRect, dwStyle, FALSE, dwExStyle);  // Adjust window to true resqusted
324     
325     /*
326      *  WS_CLIPSIBLINGS and WS_CLIPCHILDREN are both REQUIRED for OpenGL to work properly. 
327      *  These styles prevent other windows from drawing over or into our OpenGL Window.
328      */
329     if (!(hWnd = CreateWindowEx(dwExStyle,                // Extended style for the window
330         "OpenGL",                                         // Class name
331         title,                                            // Window title
332         WS_CLIPSIBLINGS |                                 // Requried window style
333         WS_CLIPCHILDREN |                                 // Requried window style
334         dwStyle,                                          // Select window style
335         0, 0,                                             // Window position
336         WindowRect.right - WindowRect.left,               // Calculate adjusted window width
337         WindowRect.bottom - WindowRect.top,               // Calculate adjusted window height
338         NULL,                                             // No parent window
339         NULL,                                             // No menu
340         hInstance,                                        // Instance
341         NULL)))                                           // Don‘t pass anything to WM_CREATE
342     {
343         KillGLWindow();                                   //Reset the display
344         MessageBox(NULL, "Window creation error.", "ERROR", MB_OK | MB_ICONEXCLAMATION);
345         return FALSE;                                     // Retrurn FALSE;
346     }
347 
348     /*
349      *  aside from the stencil buffer and the (slow) accumulation buffer
350      */
351     static PIXELFORMATDESCRIPTOR pfd =                    // pfd tells windows how we want things to be 
352     {
353         sizeof(PIXELFORMATDESCRIPTOR),                    // Size of this pixel format descriptor
354         1,                                                // Version number
355         PFD_DRAW_TO_WINDOW |                              // Format must support window
356         PFD_SUPPORT_OPENGL |                              // Format must support OpenGL
357         PFD_DOUBLEBUFFER,                                 // Must support double buffer
358         PFD_TYPE_RGBA,                                    // Request an RGBA format
359         bits,                                             // Select our color depth
360         0, 0, 0, 0, 0, 0,                                 // Color bits ignored
361         0,                                                // No alpha buffer
362         0,                                                // shift bit ignored
363         0,                                                // No accumulation buffer
364         0, 0, 0, 0,                                       // Accumulation bits ignored
365         16,                                               // 16Bits Z_Buffer (depth buffer)
366         0,                                                // No stencil buffer
367         0,                                                // No auxiliary buffer
368         PFD_MAIN_PLANE,                                   // Main drawing layer
369         0,                                                // Reserved
370         0, 0, 0                                           // Layer makes ignored
371     };
372 
373     if (!(hDC = GetDC(hWnd))) {                           // Did we get a device context
374         KillGLWindow();                                   // Reset the display
375         MessageBox(NULL, "Can‘t create a GL device context.", "ERROR", MB_OK | MB_ICONEXCLAMATION);
376         return FALSE;                                     // Return FALSE
377     }
378 
379     if (!(PixelFormat = ChoosePixelFormat(hDC, &pfd))) {  // Did window find a matching pixel format
380         KillGLWindow();                                   // Reset the display
381         MessageBox(NULL, "Can‘t find a suitable pixelformat.", "ERROR", MB_OK | MB_ICONEXCLAMATION);
382         return FALSE;                                     // Return FALSE;
383     }
384 
385     if (!SetPixelFormat(hDC, PixelFormat, &pfd)) {        // Are we able to set the pixel format
386         KillGLWindow();                                   // Reset the display
387         MessageBox(NULL, "Can‘t set the pixelformat.", "ERROR", MB_OK | MB_ICONEXCLAMATION);
388         return FALSE;                                     // Return FALSE;
389     }
390 
391     if (!(hRC = wglCreateContext(hDC))) {                 // Are we able to rendering context
392         KillGLWindow();                                   // Reset the display
393         MessageBox(NULL, "Can‘t create a GL rendering context.", "ERROR", MB_OK | MB_ICONEXCLAMATION);
394         return FALSE;                                     // Return FASLE;
395     }
396 
397     if (!wglMakeCurrent(hDC, hRC)) {                      // Try to activate the rendering context
398         KillGLWindow();                                   // Reset the display
399         MessageBox(NULL, "Can‘t activate the GL rendering context.", "ERROR", MB_OK | MB_ICONEXCLAMATION);
400         return FALSE;                                     // Return FALSE    
401     }
402 
403     /*
404      *  ReSizeGLScene passing the screen width and height to set up our perspective OpenGL screen.
405      */
406     ShowWindow(hWnd, SW_SHOW);                            // Show the window
407     SetForegroundWindow(hWnd);                            // slightly higher priority
408     SetFocus(hWnd);                                       // Sets keyboard focus to the window
409     ReSizeGLScene(width, height);                         // Set up our perspective GL screen
410 
411     /*
412      *  we can set up lighting, textures, and anything else that needs to be setup in InitGL().
413      */
414     if (!InitGL()) {                                      // Initialize our newly created GL window
415         KillGLWindow();                                   // Reset the display
416         MessageBox(NULL, "Initialize Failed.", "ERROR", MB_OK | MB_ICONEXCLAMATION);
417         return FALSE;                                     // Return FALSE
418     }
419     return TRUE;
420 }
421     
422 LRESULT CALLBACK WndProc(HWND hWnd,                       // Handle for this window
423     UINT uMsg,                                            // Message for this window
424     WPARAM wParam,                                        // Additional message information
425     LPARAM lParam)                                        // Additional message information
426 {
427     switch (uMsg) {                                       // Check for window message
428         case WM_ACTIVATE: {                               // Check minimization state
429             if (!HIWORD(wParam)) {
430                 active = TRUE;                            // Program is active
431             }
432             else {
433                 active = FALSE;                           // Program is no longer active
434             }
435             return 0;                                     // Return to the message loop
436         }
437         case WM_SYSCOMMAND: {                             // Intercept system commands
438             switch (wParam) {                             // Check system calls
439                 case SC_SCREENSAVE:                       // Screensaver trying to start
440                 case SC_MONITORPOWER:                     // Monitor trying to enter powersave
441                 return 0;                                 // Prevent form happening
442             }
443             break;                                        // Exit
444         }
445         case WM_CLOSE: {                                  // Did we receive a close message
446             PostQuitMessage(0);                           // Send a quit message
447             return 0;
448         }
449         case WM_KEYDOWN: {                                // Is a key being held down
450             keys[wParam] = TRUE;                          // if so, mark it as TRUE
451             return 0;                                     // Jump back
452         }
453         case WM_KEYUP: {                                  // Has a key been released
454             keys[wParam] = FALSE;                         // if so, mark it as FALSE
455             return 0;                                     // Jump back
456         }
457         case WM_SIZE: {                                   // Resize the OpenGL window
458             ReSizeGLScene(LOWORD(lParam), HIWORD(lParam));   // LoWord = width HiWord = height
459             return 0;                                     // Jump back
460         }
461     }
462     return DefWindowProc(hWnd, uMsg, wParam, lParam);     // Pass all unhandled message to DefWindwProc
463 }
464 
465 int WINAPI WinMain(HINSTANCE hInstance,                   // Instance
466     HINSTANCE hPrevInstance,                              // Previous instance
467     LPSTR lpCmdLine,                                      // Command line parameters
468     int nCmdShow)                                         // Window show state
469 {
470     MSG msg;                                              // Window message structure
471     BOOL done = FALSE;                                    // Bool variable to exit loop
472                                                           // Ask the user which screen mode they prefer
473     if (MessageBox(NULL, "Would you like to run in fullscreen mode?",
474         "Start fullscreen?", MB_YESNO | MB_ICONQUESTION) == IDNO)
475     {
476         fullscreen = FALSE;                               // Window mode
477     }
478                                                           // Create our OpenGL window
479     if (!CreateGLWindow("Adding Color", 640, 480, 16, fullscreen)) {  // (Modified)
480         return 0;                                         // Quit if window was not create
481     }
482 
483     while (!done) {                                       // Loop that runs until donw = TRUE
484         if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) {   // Is there a message wating
485             if (msg.message == WM_QUIT) {                 // Havw we received a quit message
486                 done = TRUE;                              // if so done  = TRUE
487             }
488             else {                                        // If not, deal with window message
489                 TranslateMessage(&msg);                   // Translate message
490                 DispatchMessage(&msg);                    // Dispatch message
491             }
492         }
493         else {
494             // Draw the scene. Watch for ESC key and quit message from DrawGLScene()
495             if (active) {                                 // Program active
496                 if (keys[VK_ESCAPE]) {                    // Was ESC pressed
497                     done = TRUE;                          // ESC signalled a quit
498                 }
499                 else {                                    // Not time to quit, update screen
500                     DrawGLScene();                        // Draw scene
501                     SwapBuffers(hDC);                     // Swap buffers (double buffering)
502                 }
503             }
504 
505             /*
506              *  It allows us to press the F1 key to switch from fullscreen mode to 
507              *  windowed mode or windowed mode to fullscreen mode.
508              */
509             if (keys[VK_F1]) {                            // Is F1 being pressed
510                 keys[VK_F1] = FALSE;                      // If so make key FASLE
511                 KillGLWindow();                           // Kill our current window
512                 fullscreen = !fullscreen;                 // Toggle fullscreen / window mode
513                 //Recreate our OpenGL window(modified)
514                 if (!CreateGLWindow("Adding Color", 640, 480, 16, fullscreen)) {
515                     return 0;                             // Quit if window was not create
516                 }
517             }
518         }
519     }
520     // Shutdown
521     KillGLWindow();                                       // Kill the window
522     return (msg.wParam);                                  // Exit the program
523 }