aspect_scale.py

#!/usr/bin/python
# -*- coding: utf-8 -*-
"""
aspect_scale.py - Scaling surfaces keeping their aspect ratio
Raiser, Frank - Sep 6, 2k++
crashchaos at gmx.net

This is a pretty simple and basic function that is a kind of
enhancement to pygame.transform.scale. It scales a surface
(using pygame.transform.scale) but keeps the surface's aspect
ratio intact. So you will not get distorted images after scaling.
A pretty basic functionality indeed but also a pretty useful one.

Usage:
is straightforward.. just create your surface and pass it as
first parameter. Then pass the width and height of the box to
which size your surface shall be scaled as a tuple in the second
parameter. The aspect_scale method will then return you the scaled
surface (which does not neccessarily have the size of the specified
box of course)

Dependency:
a pygame version supporting pygame.transform (pygame-1.1+)
"""
import pygame

def aspect_scale(img,box):
    """ Scales 'img' to fit into box bx/by.
     This method will retain the original image's aspect ratio """
    bx,by = box
    ix,iy = img.get_size()
    if ix > iy:
        # fit to width
        scale_factor = bx/float(ix)
        sy = scale_factor * iy
        if sy > by:
            scale_factor = by/float(iy)
            sx = scale_factor * ix
            sy = by
        else:
            sx = bx
    else:
        # fit to height
        scale_factor = by/float(iy)
        sx = scale_factor * ix
        if sx > bx:
            scale_factor = bx/float(ix)
            sx = bx
            sy = scale_factor * iy
        else:
            sy = by
    sx = int(sx)
    sy = int(sy)

    return pygame.transform.smoothscale(img, (sx,sy))