Load Bitmap into memory in Unity using System.Drawing

Question

Using Unity 2017.4.33f1-Personal.

I'm trying to use the Image.FromFile method in the System.Drawing namespace to load a Bitmap in a GameObject's logic. Please note that I am not interested in saving this bmp as an asset or anything like that. I am only looking to load it into RAM where I can do some calculations. I have tried the following:

var result = Image.FromFile(
    AssetDatabase.GetAssetPath(mainImg)
) as Bitmap;

But I get the following error:

InvalidProgramException: Invalid IL code in System.Drawing.Image:FromFile (string): IL_0000: ret    

FYI,

• mainImg is a reference to a Texture2D resource
• AssetDatabase.GetAssetPath(mainImg) resolves to Assets/CustomPackages/SeededConstruction/PuzzleBuilder/Input/main.bmp

I've also tried a bunch of other goofy things, including getting the absolute path and replacing forward slashes with backslashes like this:

var result = Image.FromFile(    
    Directory.GetCurrentDirectory() 
    + "\\" 
    + AssetDatabase.GetAssetPath(mainTileset)
    .Replace('/', '\\')
) as Bitmap;

In this case, the path resolves to D:\_Projects\2dGenerator\PlatformGeneration\Assets\CustomPackages\SeededConstruction\PuzzleBuilder\Input\main.bmp . However, this returns the same error as above.

What am I doing wrong here? It seems like this methodology works fine in normal.Net applications, why not in Unity?

Answer 1

It turns out it was not any kind of filepath issue. In order to properly reference System.Drawing in Unity 2017.4.33f1-Personal, I took the following steps:

1. Go to Edit -> Project Settings -> Player. Change the API Compatability Level from .NET 2.0 Subset to .NET 2.0.
2. Add an mcs.rsp to my unity projects root Asset folder. Open in it in a text editor and on the first line, enter: -r:System.Drawing.dll . Save.
3. Close and reopen Unity.