ImageResizer AspectRatioPlugin

AspectRatioPlugin.cs

    /// <summary>
    /// A ImageResizerPlugin that uses a special ascpetratio command to calculate the height.
    /// </summary>
    /// <author>Per Osbäck</author>
    public class AspectRatioPlugin : IPlugin
    {
        public AspectRatioPlugin()
        {
        }

        #region IPlugin Members

        public IPlugin Install(ImageResizer.Configuration.Config c)
        {
            c.Plugins.add_plugin(this);
            c.Pipeline.Rewrite += new UrlRewritingEventHandler(Pipeline_RewriteDefaults);
            return this;
        }

        void Pipeline_RewriteDefaults(IHttpModule sender, HttpContext context, IUrlEventArgs e)
        {
            var aspectW = e.QueryString["aspectw"];
            var aspectH = e.QueryString["aspecth"];
            if (aspectH == null && aspectW == null)
            {
                return;
            }

            double aspectratio = 0;
            if (double.TryParse(aspectW ?? aspectH, out aspectratio) && aspectratio > 0)
            {
                int parameterValue = 0;
                if (aspectW != null && int.TryParse(e.QueryString["width"], out parameterValue))
                {
                    UpdateParameters("height", (int)(parameterValue / aspectratio), e);
                }
                else if (aspectH != null && int.TryParse(e.QueryString["height"], out parameterValue))
                {
                    UpdateParameters("width", (int)(parameterValue * aspectratio), e);
                }
            }
        }

        private void UpdateParameters(string targetKey, int targetValue, IUrlEventArgs e)
        {
            e.QueryString.Remove(targetKey);
            e.QueryString.Add(targetKey, targetValue.ToString());
        }

        public bool Uninstall(ImageResizer.Configuration.Config c)
        {
            c.Plugins.remove_plugin(this);
            c.Pipeline.RewriteDefaults -= new UrlRewritingEventHandler(Pipeline_RewriteDefaults);
            return true;
        }

        #endregion
    }

I like the general idea of having an aspect ratio plugin in ImageResizer! I would suggest to go with something like aspectw and aspecth to allow aspect keeping in both dimensions? So this would be more generic and not so tightly coupled to the requirements we have right now regarding slimmage/slimresponse and width/height.

Also we would need to take into account that params can be semicolon seperated (not only querystring) and there is w as well as width. But that's just details. Unchecked claim. Maybe Config.Pipeline already does that?

Thanks for the suggestion, updated gist based on your feedback.