I have implemented a little engine for drawing in opengl(2d) inside a qt interface .
Now i must implement something like at the acrobat reader’s interface :
A document area with zoom and scroll.
I don’t need perspective, but whats I use for the scrolling and the zoom?
I must do all with glortho?
I use shaders and the vbos , how i can get a matrix from glortho for send it to the shader param where is multiplied for each point?
Is like the projection transformation and the 4x4 matrix MVP(model view projection)?

and how i can translate the coordinates of qt opengl widget to the opengl viewport?

glOrtho create a matrix as described in the documentation

so… it’s really easy to create a function that do the same exact matrix as glOrtho so you don’t need to retrieve (that it’s a slow operation that cause a flush of the command buffer).

You can to all the pan and zoom by moving the glOrtho parameters.

with = windowWidth * zoomFactor
height = windowHeight * zoomFactor

left = panX
top = panY
right = left + width
bottom = top + height
glOrtho(left, right, bottom, top, 0.0, 1.0);

The matrix produced by glOrtho can be used as a projection matrix. In this case you don’t have a “view” matrix cause the projection transformation also move the the “camera”.

If you are using a QGLWidget you don’t have to translate any coordinates. Just assign the size to the viewport as showed in this tutorial
By the way, why don’t you use QGLView and QGLCamera?

very thanks.
Now that i know that exist a qt camera i use it.
But i would explain that i must do : i wish do a like acrobat reader application.
I have an a4(sheet) that is a 2d texture(just a photo or a scansion)and some text on it, but if i resizes the glwidget changes the proportions that i wish maintain.
Is possible add two scrollbars and overflow the entire sheet after the zoom?
or select only a part of the sheet with a box zoom.