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Genie81

OpenGL OpenGL Text / Fonts - using gluLookAt() - Solved

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Genie81    122
------------------------------------------------------------------------------- [caution] gluLookAt() WAS NOT THE PROBLEM [attention] To view both wglFonts & 3D objects simultaneously, switch between
gluPerspective() & glOrtho() views by using glPushMatrix() & glPopMatrix(). ------------------------------------------------------------------------------- Hi, I have a descent amount of programming experience using C++ and I have recently started looking at openGL. I started getting the basics to work, e.g. Rotating Cube, Texturing, loading in 3D files, Camera movements, etc. I have encountered a problem when I started working with fonts and displaying text at the same time while rotating a cube. I have tracked it down to one line. When I Rotate a cube in openGL I use gluLookAt() and when I use the BitmapFont example from Chapter 11 on Beginning openGL Game Programming‘s CD, I notice that it uses glOrtho(). I am not able to display the text when using gluLookAt().
My Question is: Does anyone know the solution to displaying text while using gluLookAt()?
Also Does anyone know of any good explanations on the web or forums explaining a quick & simple way to implement fonts in openGL. I wasn’t able to find any. p.s. the BitmapFont example uses wglUseFontBitmaps. Thanks [Edited by - Genie81 on March 5, 2007 2:28:30 AM]

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jouley    805
The Forum FAQ answers both your questions. Concerning how to switch from 3D to 2D mode, here's a generic method. The glLoadIdentity( ) calls basically nullify the gluLookAt( ) that has been performed, by resetting all transformations that have taken place. So, you start all over after rendering your 3D objects, and then render your text.

As far as text in OpenGL goes, you have plenty of options. Textured quads, bitmaps, and polygonal text are the big three. The third question in the FAQ deals with bitmapped fonts (as you've already used). Here's a good overview of the three methods I mentioned, from OpenGL's own pages, even.

If some research and tinkering leads you nowhere, or if you have any other questions, post 'em up!
-jouley

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Genie81    122
Thanks Jouley for the great links.
The Forum FAQ link brought me to Nehe's lesson 13. I have previously looked at that example but it uses gluPerspective(). The second link here uses glOrtho(). I am able to get text to display in different ways using openGL but not in the gluLookAt() perspective.
I was wondering if you know a way to display Bitmap text when viewing objects in gluLookAt() mode?
Thanks again for the quick response.

[Edited by - Genie81 on March 4, 2007 11:59:55 PM]

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jouley    805
You say you are unable to display the text when using gluLookAt( ). What doesn't display correctly? Does the text show up, just not where you want/think it should? More detailed information, as well as any pertinent code (inside of [source] and [/source] tags) that you're using would really help to answer your questions about bitmap fonts with gluLookAt( ).

The reason I pointed you to the 2D rendering with OpenGL link was to open up the possibility of using both types of projections within the same scene. You can render your cube and other objects using a perspective projection, and then switch to orthographic for your text. This may be able to give you the results you want (Speaking of which, what sort of results are you looking for?) more easily than actually using gluLookAt( ) for both the cube and the text.

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Genie81    122
The results I am looking for is a small opengl program that uses gluLookAt() to view a rotating cube and have "Hello World" written in the upper-left corner of the screen. I have combined two small programs from the CD I mentioned earlier and created a program which can either display text or the rotating cube.

I am able to view both with gluLookAt() now however when I use
gluPerspective(52.0f,(GLfloat)width/(GLfloat)height,1.0f,1000.0f);

I see the 3D cube but not the text and when I use
glOrtho(0.0f, width - 1.0, 0.0, height - 1.0, -1.0, 1.0);

I see the text but not the 3D cube behind it. I can't view both the text and 3D cube at the same time as I would like.

Source code:
#ifdef _WINDOWS
#include <windows.h>
#endif

#include <gl/gl.h>
#include <gl/glu.h>
#include <math.h>
#include "CGfxOpenGL.h"

// disable implicit float-double casting
#pragma warning(disable:4305)
float rotquad;
extern HDC hDC;

CGfxOpenGL::CGfxOpenGL()
{
}

CGfxOpenGL::~CGfxOpenGL()
{
}

bool CGfxOpenGL::Init()
{
glShadeModel(GL_SMOOTH);
glClearColor(0.0, 0.0, 0.0, 0.0);
glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LEQUAL);

m_fontListBase = CreateBitmapFont("Verdana", 36);
return true;
}

bool CGfxOpenGL::Shutdown()
{
ReleaseFont(m_fontListBase);
return true;
}

void CGfxOpenGL::SetupProjection(int width, int height)
{
if (height == 0) // don't want a divide by zero
{
height = 1;
}

glViewport(0, 0, width, height); // reset the viewport to new dimensions
glMatrixMode(GL_PROJECTION); // set projection matrix current matrix
glLoadIdentity(); // reset projection matrix

// calculate aspect ratio of window

gluPerspective(52.0f,(GLfloat)width/(GLfloat)height,1.0f,1000.0f); //This perspective shows the 3D cube
//glOrtho(0.0f, width - 1.0, 0.0, height - 1.0, -1.0, 1.0); //This perspective shows the Text

glMatrixMode(GL_MODELVIEW); // set modelview matrix
glLoadIdentity(); // reset modelview matrix

m_windowWidth = width;
m_windowHeight = height;
}

void CGfxOpenGL::Prepare(float dt)
{

}
void CGfxOpenGL::DrawCube()
{
glTranslatef(0.0f, 1.0f,-5.0f); // Translate Into The Screen 7.0 Units
glRotatef(rotquad,0.0f,1.0f,0.0f); // Rotate The cube around the Y axis
glRotatef(rotquad,1.0f,1.0f,1.0f);
glBegin(GL_QUADS); // Draw a cube with quads
glColor3f(0.0f,1.0f,0.0f); // Color Blue
glVertex3f( 1.0f, 1.0f,-1.0f); // Top Right Of The Quad (Top)
glVertex3f(-1.0f, 1.0f,-1.0f); // Top Left Of The Quad (Top)
glVertex3f(-1.0f, 1.0f, 1.0f); // Bottom Left Of The Quad (Top)
glVertex3f( 1.0f, 1.0f, 1.0f); // Bottom Right Of The Quad (Top)
glColor3f(1.0f,0.5f,0.0f); // Color Orange
glVertex3f( 1.0f,-1.0f, 1.0f); // Top Right Of The Quad (Bottom)
glVertex3f(-1.0f,-1.0f, 1.0f); // Top Left Of The Quad (Bottom)
glVertex3f(-1.0f,-1.0f,-1.0f); // Bottom Left Of The Quad (Bottom)
glVertex3f( 1.0f,-1.0f,-1.0f); // Bottom Right Of The Quad (Bottom)
glColor3f(1.0f,0.0f,0.0f); // Color Red
glVertex3f( 1.0f, 1.0f, 1.0f); // Top Right Of The Quad (Front)
glVertex3f(-1.0f, 1.0f, 1.0f); // Top Left Of The Quad (Front)
glVertex3f(-1.0f,-1.0f, 1.0f); // Bottom Left Of The Quad (Front)
glVertex3f( 1.0f,-1.0f, 1.0f); // Bottom Right Of The Quad (Front)
glColor3f(1.0f,1.0f,0.0f); // Color Yellow
glVertex3f( 1.0f,-1.0f,-1.0f); // Top Right Of The Quad (Back)
glVertex3f(-1.0f,-1.0f,-1.0f); // Top Left Of The Quad (Back)
glVertex3f(-1.0f, 1.0f,-1.0f); // Bottom Left Of The Quad (Back)
glVertex3f( 1.0f, 1.0f,-1.0f); // Bottom Right Of The Quad (Back)
glColor3f(0.0f,0.0f,1.0f); // Color Blue
glVertex3f(-1.0f, 1.0f, 1.0f); // Top Right Of The Quad (Left)
glVertex3f(-1.0f, 1.0f,-1.0f); // Top Left Of The Quad (Left)
glVertex3f(-1.0f,-1.0f,-1.0f); // Bottom Left Of The Quad (Left)
glVertex3f(-1.0f,-1.0f, 1.0f); // Bottom Right Of The Quad (Left)
glColor3f(1.0f,0.0f,1.0f); // Color Violet
glVertex3f( 1.0f, 1.0f,-1.0f); // Top Right Of The Quad (Right)
glVertex3f( 1.0f, 1.0f, 1.0f); // Top Left Of The Quad (Right)
glVertex3f( 1.0f,-1.0f, 1.0f); // Bottom Left Of The Quad (Right)
glVertex3f( 1.0f,-1.0f,-1.0f); // Bottom Right Of The Quad (Right)
glEnd(); // End drawing cube with quads

rotquad +=0.1f;
}
void CGfxOpenGL::Render()
{
// clear screen and depth buffer
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

// load the identity matrix (clear to default position and orientation)
glLoadIdentity();
gluLookAt(0, 1, 1, 0, 1, 0, 0, 1, 0);

glColor3f(1.0f, 1.0f, 1.0f);
RenderFont(270, m_windowHeight/2, m_fontListBase, "Hello World!");
DrawCube();
}
unsigned int CGfxOpenGL::CreateBitmapFont(char *fontName, int fontSize)
{
HFONT hFont; // the windows font
unsigned int base;

base = glGenLists(96);

if (!stricmp(fontName, "symbol"))
{
hFont = CreateFont(fontSize, 0, 0, 0, FW_BOLD, FALSE, FALSE, FALSE,
SYMBOL_CHARSET, OUT_TT_PRECIS, CLIP_DEFAULT_PRECIS,
ANTIALIASED_QUALITY, FF_DONTCARE | DEFAULT_PITCH,
fontName);
}
else
{
hFont = CreateFont(fontSize, 0, 0, 0, FW_BOLD, FALSE, FALSE, FALSE,
ANSI_CHARSET, OUT_TT_PRECIS, CLIP_DEFAULT_PRECIS,
ANTIALIASED_QUALITY, FF_DONTCARE | DEFAULT_PITCH,
fontName);
}

if (!hFont)
return 0;

SelectObject(hDC, hFont);
wglUseFontBitmaps(hDC, 32, 96, base);

return base;
}
void CGfxOpenGL::ReleaseFont(unsigned int base)
{
if (base != 0)
glDeleteLists(base, 96);
}
void CGfxOpenGL::RenderFont(int xPos, int yPos, unsigned int base, char *str)
{
if ((base == 0) || (!str))
return;

glRasterPos2i(xPos, yPos);

glPushAttrib(GL_LIST_BIT);
glListBase(base - 32);
glCallLists((int)strlen(str), GL_UNSIGNED_BYTE, str);
glPopAttrib();
}





[Edited by - Genie81 on March 5, 2007 1:52:34 AM]

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ne0_kamen    371
Well you can use
[SOURCE]glViewport(0, 0, xfin, yfin);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0f,1.0f* xfin /yfin, 0.1f, 50.0f);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
[/SOURCE]

at the init of your program and then draw the cube.Then you set ortho mode this way
[SOURCE]
// switch to projection mode
glMatrixMode(GL_PROJECTION);
glPushMatrix();
// reset matrix
glLoadIdentity();
//Set the viewport
glViewport(xstart,ystart,xfin,yfin);
// set a 2D orthographic projection
glOrtho(0, xfin, yfin, 0, -5.0f, 20.0f);
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadIdentity();
[/SOURCE]

draw the text and then call
[SOURCE]
glMatrixMode(GL_PROJECTION);
glPopMatrix();
glMatrixMode(GL_MODELVIEW);
glPopMatrix();
[/SOURCE]

to go back in 3d mode.That should solve it.

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Genie81    122
Thanks ne0_kamen!!!
That was exactly what I was looking for. I got it to work now. I am new to openGL so I didn't realise that I have to push & pop projections from the stack in order to switch back and forth from the projections. Is this an efficient way to achieve the result of having both text and 3D objects on the screen. Also do you know if using wglUseFontBitmaps(); for displaying text has any disadvantages?

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