glViewport query

[jyotigoyal]

Hi
I am new to gtkglext trying to run some simple sample programs.
In gtkglext, we create a drawing area as a widget and then set the size of the viewport using glviewport().Is the size of the drawing area not same as the size of the viewport? If not,then y? why would anyone make the size of drawing area and viewport different when viewport is also used to limit the size of drawing area?
Also where is the coordinate (0,0) located on a window in this case?
for gtk applications,it is located at top left corner.for gtkglext,where is it located? I am getting confused with the negative coordinates used in glviewport and glrectf and similar fns.

[psharma]

Hi ,

glViewport specifies the affine transformation of x and y from normalized device coordinates to window coordinates and could be different than size of the widget. Try setting it to (w/2 , h/2 ) and (2*w, 2*h) to see the difference. You could zoom in or out using viewport with same widget size.
(0,0 ) is the lower left corner of the viewport  rectangle

~Prashant

On Fri, Jul 10, 2009 at 7:41 PM, jyotigoyal <jytgyl@...> wrote:

Hi
I am new to gtkglext trying to run some simple sample programs.
In gtkglext, we create a drawing area as a widget and then set the size of
the viewport using glviewport().Is the size of the drawing area not same as
the size of the viewport? If not,then y? why would anyone make the size of
drawing area and viewport different when viewport is also used to limit the
size of drawing area?
Also where is the coordinate (0,0) located on a window in this case?
for gtk applications,it is located at top left corner.for gtkglext,where is
it located? I am getting confused with the negative coordinates used in
glviewport and glrectf and similar fns.
--
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[psharma]

Hi ,

glViewport specifies the affine transformation of x and y from normalized device coordinates to window coordinates and could be different than size of the widget. Try setting it to (w/2 , h/2 ) and (2*w, 2*h) to see the difference. You could zoom in or out using viewport with same widget size.
(0,0 ) is the lower left corner of the viewport  rectangle

~Prashant

jyotigoyal wrote:

Hi
I am new to gtkglext trying to run some simple sample programs.
In gtkglext, we create a drawing area as a widget and then set the size of the viewport using glviewport().Is the size of the drawing area not same as the size of the viewport? If not,then y? why would anyone make the size of drawing area and viewport different when viewport is also used to limit the size of drawing area?
Also where is the coordinate (0,0) located on a window in this case?
for gtk applications,it is located at top left corner.for gtkglext,where is it located? I am getting confused with the negative coordinates used in glviewport and glrectf and similar fns.