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True OpenGL Zooming

By , 11 Feb 2002
 

Sample Image - Zoom.jpg

Introduction

The topic of this article is focused around zooming in a perspective OpenGL view. I wrote this article because I found some examples of zooming in a OpenGL view using ortho projections. But the most advanced example that I found using perspective projections, don't implement a true zooming but simulate the zooming effect changing the view point or camera angle. The technique that I suggest implement a true zooming and not change camera angle or perspective parameters (view point, reference point clipping planes). I achieved this result using the function glFrustum instead of standard gluPerspective and manipulating (see function COGL::SetPerspective(const CRect &rcClient) in the class COGL) the scaling and translating parameters of projection matrix. Two normalized rectangles are maintained by the COGL class: one for the full size image, and one for the current zooming rectangle. The image presented by OpenGL is scaled by the ratio of the rectangles, adjusted according to the viewport aspect and translated to the center of current zooming rectangle.

Finally sorry for my poor English.

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GeneralAbout 3D pointmemberEduardo Tucci29-Jun-10 15:54 
I would like to know if when I click on screen I can transform 2D mouse point to 3D point. if yes, How can I to do this?
QuestionPanning in perspective view?memberHan Wu17-Nov-06 5:27 
The code for implementing the zoom window in perspective view is just perfect. It show's that, you have a deep understanding of how to create a perspective matrix. I would like to know whether you have written any article about Panning in Perspective view or not? I would be appreciated if you could show me how to do true panning in perspective view.
 
Thanks.
Generali want to use 3dmax , opengl and c#membereey5630-Oct-06 21:53 
I want to use 3dmax objects on the .net platform(use c# code) and also i use opengl code.Do you have any opinion about this.Please give me a example project.
 
Thank you...
 
eey56@yahoo.com
Generalopengl control ...memberdoudicool5-May-06 11:34 
hi ,can you tell me how can i introduce buttons ,edit zone ,all this beside an opengl child window in viual c++6.0 or in builderC++ 6.0 i am verry confused ...thank you .....
 
-- modified at 17:37 Friday 5th May, 2006
GeneralAdd Scroll Barmemberanil6-Sep-05 22:14 
Hello Friend
Can any body tell me how to add scroll bar to this Zoom.
 
Regards
Anil
Generalzoomingmembersreejith ss nair28-Apr-05 20:24 

I have a winform application. One of my winform contain a panel with few child controls. I would like to impliment zooming (like 50 % , 100 % etc) facility for all child controls which are avilable inside that panel.
The main reason is, i have a collection of controls inside that perticular panel. Sometime user want to see some or all controll at a streach without scrolling panel up and down.
 

How will do this ? Please post your idea.

 
Sreejith Nair
[ My Articles ]
QuestionHow To Load 3DMax Objects in OpenGL?memberobaid salikeen25-Apr-05 23:31 
hi,
i want to import a 3DMax object in my opengl project, i have used 3DSloader, but my project is now dead slow. i want to load all the objects efficiently. i tried to read all the vertices in an array to draw them, but it does not work. a hint or a code sample will help.
email:
obaid_salikeen@hotmail.com
Generalis it possible to use it for dialogsmembernandeeshds28-Oct-04 5:05 
hi frnd
 
is it possible to use ur beutiful zooming to zoom a bitmap on a dialog.
 
help me out
QuestionHow to run 2 different(or same) OpenGL objects in one DialogBox?memberwerter13-May-04 21:10 

How to run 2 different(or same) OpenGL objects in one DialogBox?
IDC_STATIC1 is a first OpenGL objects Scene window.
IDC_STATIC2 is a second OpenGL objects Scene window.
IDC_STATIC1 and IDC_STATIC2 ,they are placed on IDD_DIALOG1.
 
code:
pclStatic = (CStatic *)GetDlgItem(IDC_OpenGL_Window);
pclGlView = new CGlView(pclStatic);
pclGlView->OnCreate();
pclGlView->InitGL();
pclGlView->DrawGLScene();
 
pclStatic1 = (CStatic *)GetDlgItem(IDC_OpenGL_Window);
pclGlView1 = new CGlView(pclStatic1);
pclGlView1->OnCreate();
pclGlView1->InitGL();
pclGlView1->DrawGLScene();
 
Will not involve both windows (IDC_STATIC2,IDC_STATIC1)
QuestionHOW TO DRAW A CIRCULAR SCALE?memberprath8-Apr-03 2:46 
Cry | :(( HOW TO DRAW A CIRCULAR SCALE (similar to a time clock showing graduations outwards in degrees 0,5,...360.
any code...?
Questionhow to ZOOM?memberprath8-Apr-03 2:43 
Cry | :(( HOW TO ZOOM a particular part of colour buffer content.
could i know any more links...to articles,codes,tutorials
General3D coordinatemembereddymohd19-Feb-03 22:24 
How can i translate the 2D coordinate of the screen into opengl 3D coordinate?
GeneralRe: 3D coordinatemembertopus19-May-03 2:21 
int gluUnProject(
GLdouble winx,
GLdouble winy,
GLdouble winz,
const GLdouble modelMatrix[16],
const GLdouble projMatrix[16],
const GLint viewport[4],
GLdouble *objx,
GLdouble *objy,
GLdouble *objz
);
Parameters
winx, winy, winz
The window coordinates to be mapped.
modelMatrix
The modelview matrix (as from a glGetDoublev call).
projMatrix
The projection matrix (as from a glGetDoublev call).
viewport
The viewport (as from a glGetIntegerv call).
objx, objy, objz
The computed object coordinates.
Sleepy | :zzz:
GeneralRe: 3D coordinatesussAnonymous9-Jun-05 4:58 
u must get the unprojection matrix

GeneralSmall question about OpenGLmemberAnonymous28-May-02 0:05 
Hi all, here is the small trouble of a new-comer to OpenGL. Who knows how to convert a 3D point to a normal point (screen coordinate) and how to do on the contrary.
For example:
CRect rc;
GetClientRect(rc);
int x, y;
double u, v, t;
 
// And how to do this
// 1. M1(1.0, -0.7, 2.3) --> M2(x, y) ;
// 1. M2(100, 120) --> M1(u, v, t);
// where x in [rect.left, rect.right] and y in [rect.top, rect.bottom]
By the way, who can tell me how to load the current matrix to an array (double mymatrix[16]).
Please help me.
Thanks for your care
Smile | :)
GeneralRe: Small question about OpenGLmemberAli Khanlarkhani19-Jan-03 0:33 
This is how M3D(x, y, z) can be convert to M2D(x, y):
 
void Project(double x3D, double y3D, double z3D, double *pXWin, double *pYWin)
{
/* -------{ VARIABLE SECTION }------- */
GLdouble model_matrix[16];
GLdouble project_matrix[16];
GLint viewport[4];
double dummy_z;
/* -------{ INITIALIZATION SECTION }------- */
// Make Current Rendering context
/* -------{ MAIN SECTION }------- */
glGetDoublev(GL_MODELVIEW_MATRIX, model_matrix);
glGetDoublev(GL_PROJECTION_MATRIX, project_matrix);
glGetIntegerv(GL_VIEWPORT, viewport);
gluProject(x3D, y3D, z3D, model_matrix, project_matrix, viewport, pXWin, pYWin, &dummy_z);
/* -------{ RETURN SECTION }------- */
return;
}

GeneralHey ManmemberRick York16-Feb-02 13:09 
I just noticed that there is a link to this article at http://www.opengl.org. Very Cool ! Smile | :)
GeneralAn Easier Way....memberFatBuddha13-Feb-02 7:34 
You could of course just do exactly the same thing using gluPickMatrix:
 
//Initialise projection mode,...
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
 
//...get viewport details,...
int viewport[4];
glGetIntegerv(GL_VIEWPORT, viewport);
 
//...and create 'zoomport' details just like a normal viewport.
int zoomport[4];
zoomport[0] = //X of top left of zoom area
zoomport[1] = //Y of top left of zoom area
zoomport[2] = //Width of zoom area
zoomport[3] = //Height of zoom area
 
//Then use pickmatrix to zoom in on this part of the scene...
gluPickMatrix(zoomport[0]+zoomport[2]/2, zoomport[1]+zoomport[3]/2, zoomport[2], zoomport[3], viewport);
 
//...then set up your perspective view frustrum as normal
gluPerspective(m_FOV, m_ViewportAspect, m_FrustrumNear, m_FrustrumFar);
 
You figure out the zoomport values by catching mouse button up/down events, and you
can make a picking triangle in Windows using the DrawDragRect() function.
 
No disrespect intended to the author of this fine tutorial - just figured that some folks are looking for the meat.Smile | :)
 
FatBuddha:
 
None
GeneralRe: An Easier Way....memberpepito sbarzeguti13-Feb-02 21:30 
And if you change the size of window work ?
GeneralRe: An Easier Way....memberFatBuddha14-Feb-02 7:00 
You need to scale up the zoom values when the window is resized which is no biggy. Having said that, it is neater to alter the zoom values to be percentages of the original viewport window.
 
This means that you don't have to alter your zoom values on a window resize - and you can re-zoom much more easily. That's what I use anyhow.
 
Rob
 
None
GeneralRe: An Easier Way....memberAlberto Bencivenni12-Dec-05 3:06 
Is this method applicable to parallel mode too?
 
Can I implement the mouse wheel zoom-in zoom-out seamlessy with this approach?
 
Thanks,
 
Alberto
 

GeneralRe: An Easier Way....membera_david12321-Jun-07 23:36 

Dear FatBuddha
 
Regards!
Thanks for your reply on CodeGuro forums.
kindly help me in more detail,kindly helpe me while writing complete code for Zoom as i am the begginner.
 
hope you would help me.
Regards
David

 
david

GeneralBroken link'smemberpepito sbarzeguti12-Feb-02 6:36 
Sorry broken link's fixed. Pepito
QuestionHOW to scroll with a scrollbar in openglmembersyphax5119-Apr-04 1:20 
when u want to scroll i lose my opengl coordinates stored in display lists
please help !!!!!!
 
syphax

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