[skrebbel]

This might sound like a small thing but the .NET image processing stuff has traditionally depended a lot on Windows builtins. Mono shipped an entire mediocre rewrite of GDI (the graphics layer that's been Windows since the early nineties) just to support the .NET Framework image processing stuff. Note: not for image display (which is what GDI is mainly for) - even for headless image processing.

In practice this meant that if you were cropping an image server-side in C# code on a Linux server, a C-rewrite of a Windows UI layer would kick in and do the work for you. Amazing work from the Mono team, because it worked, but also pretty nuts.

If there's one place I remember having stuff that "just worked" on Windows and had weird subtle quirks on Mono, it's image processing (I'm talking a few years ago). So IMO it's pretty awesome that they're replacing all that legacy with a decent 100% .NET image processing library.

(Sidenote: this was also the only real problem we faced developing a C# backend with a team on Windows, Linux and OSX computers, and running it all on Mono on Docker on Linux - all well before .NET Core. Mono really is/was that good)

[ygra]

Mono shipped a reimplementation of the types in the System.Drawing namespace which uses GDI+ (note the +) on Windows. This reimplementation is also what CoreCompat.System.Drawing is based on. To my knowledge Mono did shim a few Windows APIs, mostly related to window messages so WndProc can be overridden in a useful manner, but not actually GDI, as far as I know.

[kodfodrasz]

And the implementation was buggy as hell. When I needed to resize pictures on mono + Linux I finally had to resort to manually building libgb, writing a simple wrapper for the resizing part, and use that, as back then every other alternative as either incomplete, or pain to use and/or buggy.

Note: libgd is a well designed native library with design emphasis on simple interop wrappability.

[jsingleton]

This makes sense as System.Drawing (aka GDI+) was mainly used for WinForms and has never been supported for web servers. I suspect Mono ported it to support their Windows Forms port.

It may just work on Windows but it won't keep working when used server-side in a web app. MS specifically recommend against using it in ASP.NET. I learned the hard way what happens if you ignore the warnings when I was supporting a site that did this.

Edit: I wrote about image optimization and resizing in chapter four of my book on ASP.NET Core - https://unop.uk/book/

[jamessouth]

I may have to buy that!