size of screen depends on what?

OpenGL OpenGL: Basic Coding
1

hello sir

i m trying to know how size of window i.e. height and width

and gluOrtho effect the unit of translation in opengl

i.e size is width=500,height=500 and glOrtho(-4.0,4.0,-4.0,4.0,-30,30);
and if i write glTranslatef(-4.0,0.0,0.0);
then object will go to right end of window
but if we give width =800 and height =500
then same object will not go to at end

i m not getting the relation …
thanks

2

Forgot about glViewport ? Change the viewport too any times your window size changes.

3

void glOrtho( GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble nearVal, GLdouble farVal);

That is the definition of glOrtho. It defines a parallel projection matrix using what ever values you like.
Typically you would use this to define a “2D” overlay to your main scene. If you want that then you’d typcially like to use a convienient x and y coordinate scheme. I find using the window width and height convienient as so endup with:


glviewport (0,0,width,height)
glMatrixMode (GL_PROJECTION)
glLoadidentity
glOrtho (0,0, width, height, 1, 100) 
glMatrixMode (GL_MODELVIEW)
glLoadidentity

which means that (0,0) is the bottom left corner of the window and (width,height) is the upper right corner.

4

if i will do this then unit size of translation will change with it ?..

i used it but i didn’t get proper solution to my problem…

eg…glTranslatef(1.0,0.0,0.0);

will the length taken in one unit movement (in x direction here) will change with change in view port size??
thanks