How to keep the same zoom level?

Question

How do I keep the same zoom level such that the image resolution is always the same?
i.e. when I change the viewport size the zoom level should stay the same

for example if this is my view:

when I change the viewport size everything in the view shrinks:

what I need is for it to stay the same size, more like changing the size of the viewport would be like cropping:

so how do I achieve this?

Answer 1

I found the solution here

import bpy
def scale_view(context, data, flip=False):
    rd = context.region_data
    wmat = rd.window_matrix
asp_prev = data["aspect"]
asp_curr = data["aspect"] = wmat[0][0] / wmat[1][1]

if flip:
    asp_prev = 1 / asp_prev
    asp_curr = 1 / asp_curr

if asp_curr < 1.0:
    mul = asp_prev / asp_curr
    rd.view_distance *=  mul



def on_redraw(context, cache={}):
    region = context.region
    rw = region.width
    rh = region.height
    try:
        data = cache[region]
    except:
        w = context.region_data.window_matrix
        cache[region] = {"aspect": (w[0][0] / w[1][1]), "rw": rw, "rh": rh}
else:
    if rw != data["rw"]:
        scale_view(context, data)
        data["rw"] = rw

    elif rh != data["rh"]:
        scale_view(context, data, flip=True)
        data["rh"] = rh


if name == "main":
    bpy.types.SpaceView3D.draw_handler_add(
        on_redraw, (bpy.context,), 'WINDOW', 'POST_PIXEL')