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Posted
11 Feb 2002

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HOW TO DRAW A CIRCULAR SCALE (similar to a time clock showing graduations outwards in degrees 0,5,...360.
any code...?





HOW TO ZOOM a particular part of colour buffer content.
could i know any more links...to articles,codes,tutorials





How can i translate the 2D coordinate of the screen into opengl 3D coordinate?





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.





u must get the unprojection matrix





Hi all, here is the small trouble of a newcomer 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





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;
}





I just noticed that there is a link to this article at http://www.opengl.org. Very Cool !





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.
FatBuddha:
None





And if you change the size of window work ?





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 rezoom much more easily. That's what I use anyhow.
Rob
None





Is this method applicable to parallel mode too?
Can I implement the mouse wheel zoomin zoomout seamlessy with this approach?
Thanks,
Alberto





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





Sorry broken link's fixed. Pepito







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