Alternative to System.Drawing for breaking an image into separate tiles in Unity

Question

As far as I can tell, System.Drawing namespace is not available in unity. I there an alternative library to load and manipulate or generate images on the fly?

Example: Imagine you want to make a jigsaw puzzle game and want to load and chop random images to use as textures or such.

EDIT: specifically I want to crop images and draw patches from one image onto another image. Or overlay images with grids.
Ultimately all the resulting images need to end up as textures on game objects. If need be, I can use texture.EncodeToPNG to save a copy for other purposes or for as a cached result.

EDIT AGAIN: Let's stick to a concrete example.
Player selects a photo from their iPhone library. It is chopped into pieces and appears on 9 cubes. the player need to arrange the cubes in the correct way to recreate the original image.

Answer 1

Quoting my first comment as requested:

Since one of the largest responsibilities of a game engine is rendering, this functionality is found in quite a few different classes - Texture2D, RenderTexture, Material, Camera, Graphics, Renderer... You're unlikely to find a 1:1 replacement for the way you'd do it in GDI+, but if you give more details about your specific use case we can suggest Unity-friendly ways to achieve it

In this case, it sounds like we won't need to do any image modification or generation to get this outcome in Unity. We can use the existing texture scaling & offset capabilities of the built-in shaders.

Here's an example of one image split across 9 quads:

Here all I've done is create a material instance for each piece. I've set the tiling x & y to 1/3, and used a different offset for each piece (every unique x-y combination of 0, 1/3, 2/3)

All of the materials are referencing the same single texture in memory, with no need to modify it or duplicate it into separate sections.

You can either prepare these materials ahead of time in the editor, and assign their texture to reference the one the user selected at runtime, or you can create these materials wholly at runtime and align their texture sections using the Material.mainTextureScale and Material.mainTextureOffset setters.

The same trick works for cubes (you just need to be careful of the face orientation)

(This does result in one draw call per piece, but for such a small number of pieces this isn't anything to worry about. If you were dealing with much more complex scenes, you could instead create a mesh where each quad's UVs reference only the part of the texture it needs, then render the whole mesh with one material, but that's overkill for a small puzzle)