//Title: forceAspectRatio
//Credit to: DarkCampainger
//Contributed by: DarkCampainger
//Special thanks to: Beatmewithastick (for posting the question)

/*
This verb resizes the passed window to the passed aspect ratio, tracking the
  window's previous size so it knows if it should grow or shrink. Use this verb
  by calling it from the the desired window's Resize command:
    forceAspect [window] [aspectRatio]
    forceAspect "default" 1.3333

It is recommended that you manually call this verb when the player logs in,
  so the system can set up the lastWindowWidth/Height lists and correctly
  interpret the user's resize as a grow or shrink.
*/

client
    // We track the previous window size to determine if the user is trying to
    //   shrink or grow the window
    var/tmp/lastWindowWidth = list() // Associative list of "window" = width
    var/tmp/lastWindowHeight = list() // Associative list of "window" = height

    // This verb should be called from the "Resize command" of the window you
    //   want to constrain. Pass its name and the aspect ratio.
    //   Example: forceAspect "default" 1.3333
    verb/forceAspect(window="default" as text|null, aspect=4/3 as num|null)
        var
            // Get and parse the width/height of the window's size
            size = winget(src, window, "size")
            delimiter = findtext(size, "x")
            width = text2num(copytext(size, 1, delimiter))
            height = text2num(copytext(size, delimiter+1, 0))

            // Calculate the counterpart to each dimension that would give the
            //    desired aspect ratio
            heightForWidth = round(width/aspect) // Height based on width
            widthForHeight = round(height*aspect) // Width based on height

        // Determine if the user is stretching or shrinking the window
        var
            // Calculate the changes in width/height from the previous window size
            changeWidth = (!lastWindowWidth[window] ? 0 \
                    : width - lastWindowWidth[window])
            changeHeight = (!lastWindowHeight[window] ? 0 \
                    : height - lastWindowHeight[window])

            // Take the greatest change, and see if it's an increase or decrease
            //   For an increase, we assume the user is growing the window
            grow = ((abs(changeWidth) > abs(changeHeight)) ? changeWidth : changeHeight) >= 0

        // If we're growing to fit and the height deviates the most,
        //   Or if we're shrinking to fit and the width deviates the most
        if((grow && widthForHeight>width) || (!grow && widthForHeight<width))
            // Reconstrain the width to the height
            width = widthForHeight
        else
            // Otherwise reconstrain the height to the width
            height = heightForWidth

        // Store the size so we know next time if they're shrinking or stretching the window
        lastWindowWidth[window] = width
        lastWindowHeight[window] = height

        // Update the window size
        winset(src, window, "size='[width]x[height]'")