Need some urgent help please.. with picking camera/viewing model

Hi, I have a model that I want to display using OpenGL. Right now I just want to reliably display the whole model on screen. What is the best way to do this? I know the bounding box of the model (just by calculating min x, min y, etc.)
I need to be able to see the model, I tried glortho, etc. I don’t know what parameters to pick. Basically I just need a combination of a projection transform (glOrtho, glFrustum, or whatever) + some sort of way to place the camera angle. I really have no preference with respect to the camera angle as long as the whole object is visible. Please please help…

Don’t worry!We can solve your problems.
Note: I have copied a sample source for you. But first read my comments.

There are some reasons that the programmer can’t see the object. First of all, we should consider the view volume in our program.we should use from a reshape function in our program to set the view volume and the viewport. here’s a good reshape function:

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

}

ow move to the display function. Which values should we use with this view volume? here’s some examples:
glBegin( GL_LINES );
glVertex3f( -1.0f, -1.0f, -3.0 );
glVertex3f( 1.0f, 1.0f, -3.0 );
glEnd();

Well. if you compile the program, you should see a line that is in the screen. change the values.see the results. The third value in the glVertex3f() is too important. You lines are drawn relative to the current coordinate system.your camera has been inserted in the pont (0,0,0) and it’s direction is to the negative z axis.Also the center your default coordinate system is in the place that your camera has been inserted. So IN THIS CASE, IF YOU WANT TO SEE YOUR OBJECTS, YOU SHOULD MOVE THEM TO THE NEGATIVE Z AXIS.Remember that glVertex() doesn’t affect the current coordinate system. it only uses from it.You can get the same results with the following code in your display function:
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
glTranslatef( 0.0f, 0.0f, -3.0f );
glBegin( GL_LINES );
glVertex3f( -1.0f, -1.0f, 0.0 );
glVertex3f( 1.0f, 1.0f, 0.0 );
glEnd();

But in this case, you move the coordinate system in the negative z direction and then draw the lines in this new coordinate system.

Ok. Now we should draw some more complicated models:)
First off all, enable the ighting in your initialize function with the functions:
glEnable( GL_LIGHTING );
glEnable( GL_LIGHT0 );

Then use from the following code in your display function:
glMatrixMode( GL_MODELVIEW );
glLoadIdentity();
glTranslatef( 0.0f, 0.0f, -3.0f );
glRotatef( 20, 1.0f, 1.0f, 1.0f );
auxSoildCube( 0.5 );

Try to change the values of the function auxSolidCube().

The next thing that you should consider is the lighting. but it’s sufficient for now.

I have copied the source code. See the functions ReSizeGLScene, InitGL and DrawGLScene.It’s based on the lesson 1 of the NeHe examples.

/*

  •  This Code Was Created By Jeff Molofee 2000
    
  •  A HUGE Thanks To Fredric Echols For Cleaning Up
    
  •  And Optimizing This 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
#include <gl\glut.h>
HDC hDC=NULL; // Private GDI Device Context
HGLRC hRC=NULL; // Permanent Rendering Context
HWND hWnd=NULL; // Holds Our Window Handle
HINSTANCE hInstance; // Holds The Instance Of The Application

double m_timeNow = 0.0;
double m_elapsedTime = 0.0;
double m_previousTime = 0.0;

bool keys[256]; // Array Used For The Keyboard Routine
bool active=TRUE; // Window Active Flag Set To TRUE By Default
bool fullscreen=TRUE; // Fullscreen Flag Set To Fullscreen Mode By Default

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

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
glEnable( GL_LIGHTING );
glEnable( GL_LIGHT0 );

return TRUE;										// Initialization Went OK

}

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
static float angle ;

glTranslatef( 0.0f, 0.0f, -3.0f );
glPushMatrix();
glRotatef( 50, 1.0f, 1.0f, 1.0f );
auxSolidCube( 0.5 );
glPopMatrix();

return TRUE;										// Everything 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("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
}

}

/* 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* title, int width, int height, int bits, bool fullscreenflag)
{
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	= "OpenGL";								// 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

Your 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
							"OpenGL",							// 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

}

LRESULT CALLBACK WndProc( HWND hWnd, // Handle For This Window
UINT uMsg, // Message For This Window
WPARAM wParam, // Additional Message Information
LPARAM lParam) // Additional Message Information
{
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:							// Intercept System Commands
	{
		switch (wParam)							// Check System Calls
		{
			case SC_SCREENSAVE:					// Screensaver Trying To Start?
			case SC_MONITORPOWER:				// Monitor Trying To Enter Powersave?
			return 0;							// Prevent From Happening
		}
		break;									// Exit
	}

	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
{
MSG msg; // Windows Message Structure
BOOL done=FALSE; // Bool Variable To Exit Loop

// 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 (!CreateGLWindow("NeHe's OpenGL Framework",640,480,16,fullscreen))
{
	return 0;									// Quit If Window Was Not Created
}

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

		if (keys[VK_F1])						// Is F1 Being Pressed?
		{
			keys[VK_F1]=FALSE;					// If So Make Key FALSE
			KillGLWindow();						// Kill Our Current Window
			fullscreen=!fullscreen;				// Toggle Fullscreen / Windowed Mode
			// Recreate Our OpenGL Window
			if (!CreateGLWindow("NeHe's OpenGL Framework",640,480,16,fullscreen))
			{
				return 0;						// Quit If Window Was Not Created
			}
		}
	}
}

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

}

-Ehsan-

Originally posted by cesarsalad:
Hi, I have a model that I want to display using OpenGL. Right now I just want to reliably display the whole model on screen. What is the best way to do this? I know the bounding box of the model (just by calculating min x, min y, etc.)
I need to be able to see the model, I tried glortho, etc. I don’t know what parameters to pick. Basically I just need a combination of a projection transform (glOrtho, glFrustum, or whatever) + some sort of way to place the camera angle. I really have no preference with respect to the camera angle as long as the whole object is visible. Please please help…

A perfectly fine approach is documented in the OpenGL FAQ:

http://www.opengl.org/resources/faq/technical/viewing.htm#view0070

I tried the approach in the FAQ and it didn’t work… but thanks to the guy who posted the code! that was very helpful.

You’re welcome. :wink:
-Ehsan-

Originally posted by cesarsalad:
I tried the approach in the FAQ and it didn’t work…
I can assure you that the approach in the FAQ does work, what kind of problem do you have exactly?