Jeff Molofee - NeHe's OpenGL Tutorials

token=strtok(text, " "); // Parse 'text' For Words, Seperated By " " (spaces)

while (token!=NULL) // While The Token Isn't NULL

{

cnt++; // Increase The Counter

if (cnt>maxtokens) // Is 'maxtokens' Less Than 'cnt'

{

maxtokens=cnt; // If So, Set 'maxtokens' Equal To 'cnt'

}

So we have stored the first extension from our list of extensions in the variable token. Next thing to do is set the color to bright green. We then print the variable cnt on the left side of the screen. Notice that we print at 0 on the x axis. This should erase the left (white) border that we drew, but because scissor testing is on, pixels drawn at 0 on the x axis wont be modified. The border can't be drawn over.

The variable is drawn on the far left side of the screen (0 on the x axis). We start drawing at 96 on the y axis. To keep all the text from drawing to the same spot on the screen, we add (cnt*32) to 96. So if we are displaying the first extension, cnt will equal 1, and the text will be drawn at 96+(32*1) (128) on the y axis. If we display the second extension, cnt will equal 2, and the text will be drawn at 96+(32*2) (160) on the y axis.

Notice I also subtract scroll. When the program first runs, scroll will be equal to 0. So our first line of text is drawn at 96+(32*1)-0. If you press the DOWN ARROW, scroll is increased by 2. If scroll was 4, the text would be drawn at 96+(32*1)-4. That means the text would be drawn at 124 instead of 128 on the y axis because of scroll being equal to 4. The top of our scissor window ends at 128 on the y axis. Any part of the text drawn from lines 124-127 on the y axis will not appear on the screen.

Same thing with the bottom of the screen. If cnt was equal to 11 and scroll was equal to 0, the text would be drawn at 96+(32*11)-0 which is 448 on the y axis. Because the scissor window only allows us to draw as far as line 416 on the y axis, the text wouldn't show up at all.

The final result is that we end up with a scrollable window that only allows us to look at 288/32 (9) lines of text. 288 is the height of our scissor window. 32 is the height of the text. By changing the value of scroll we can move the text up or down (offset the text).

The effect is similar to a movie projector. The film rolls by the lens, and all you see is the current frame. You don't see the area above or below the frame. The lens acts as a window similar to the window created by the scissor test.

After we have drawn the current count (cnt) to the screen, we change the color to yellow, move 50 pixels to the right on the x axis, and we write the text stored in the variable token to the screen.

Using our example above, the first line of text displayed on the screen should look like this:

1 GL_ARB_multitexture

glColor3f(0.5f,1.0f,0.5f); // Set Color To Bright Green

glPrint(0,96+(cnt*32)-scroll,0,"%i",cnt); // Print Current Extension Number

After we have drawn the current count to the screen, we change the color to yellow, move 50 pixels to the right on the x axis, and we write the text stored in the variable token to the screen.

Using our example above, the first line of text displayed on the screen should look like this:

1 GL_ARB_multitexture

glColor3f(1.0f,1.0f,0.5f); // Set Color To Yellow

glPrint(50,96+(cnt*32)-scroll,0,token); // Print The Current Token (Parsed Extension Name)

After we have displayed the value of token on the screen, we need to check through the variable text to see if any more extensions are supported. Instead of using token=strtok(text," ") like we did above, we replace text with NULL. This tells the command strtok to search from the last marker to the NEXT space in the string of text (text).

In our example above ("GL_ARB_multitexture marker GL_EXT_abgr GL_EXT_bgra") there will now be a marker after the text "GL_ARB_multitexture". The line below will start search FROM the marker to the next space. Everything from the marker to the next space will be stored in token. token should end up being "GL_EXT_abgr", and text will end up being "GL_ARB_multitexture marker GL_EXT_abgr marker GL_EXT_bgra".

Once strtok() has run out of text to store in token, token will become NULL and the loop will stop.

token=strtok(NULL," "); // Search For The Next Token

}

After all of the extensions have been parsed from the variable text we can disable scissor testing, and free the variable text. This releases the ram we were using to hold the information we got from glGetString(GL_EXTENSIONS).

The next time DrawGLScene() is called, new memory will be allocated. A fresh copy of the information returned by glGetStrings(GL_EXTENSIONS) will be copied into the variable text and the entire process will start over.

glDisable(GL_SCISSOR_TEST); // Disable Scissor Testing

free (text); // Free Allocated Memory

The first line below isn't necessary, but I thought it might be a good idea to talk about it, just so everyone knows that it exists. The command glFlush() basically tells OpenGL to finish up what it's doing. If you ever notice flickering in your program (quads disappearing, etc). Try adding the flush command to the end of DrawGLScene. It flushes out the rendering pipeline. You may notice flickering if you're program doesn't have enough time to finish rendering the scene.

Last thing we do is return true to show that everything went ok.

glFlush(); // Flush The Rendering Pipeline

return TRUE; // Everything Went OK

}

The only thing to note in KillGLWindow() is that I have added KillFont() at the end. That way whenever the window is killed, the font is also killed.

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("OpenGL", 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

}

KillFont(); // Kill The Font

}

CreateGLWindow(), and WndProc() are the same.