A translation of the code found on wikipedia to C# for use in the unity editor. (I used this to draw lines on a texture, then saved the texture as a PNG...)

DrawLineAATest.cs

using UnityEngine;
using UnityEditor;
using System.Collections;
using System.Collections.Generic;
 
public class DrawLineAATest : EditorWindow {
	
	private Texture2D tex;
	
	//http://en.wikipedia.org/wiki/Xiaolin_Wu's_line_algorithm
	void Plot(float x, float y, float c, Color col) { // is plot the pixel at (x, y) with brightness c (where 0 ≤ c ≤ 1)
		col.a = c;
		tex.SetPixel(Mathf.RoundToInt(x), Mathf.RoundToInt(y), col);
	}
	void Plot(int x, int y, float c, Color col) { // is plot the pixel at (x, y) with brightness c (where 0 ≤ c ≤ 1)
		col.a = c;
		tex.SetPixel(x, y, col);
	}
	float IntegerPart(float x) { //is return  'integer part of x'
		return Mathf.Round(x);
	}
	float Round(float x) { //is
		return IntegerPart(x + 0.5f);
	}
 
	float FractionalPart(float x) { //is return 'fractional part of x'
		return x - Mathf.RoundToInt(x);
	}
 
	float rFractionalPart(float x) { //is
		return 1f - FractionalPart(x);
	}
 
	void DrawAALine(int x0, int y0, int x1, int y1, Color col) { //is
 
		//TEMP TEST: draw point at beginning and end
		Plot(x0, y0, 1f, col);
		Plot(x1, y1, 1f, col);
 
		bool steep = Mathf.Abs(y1 - y0) > Mathf.Abs(x1 - x0);
			
		if (steep) {
			int t0 = x0;
			x0 = y0;
			y0 = t0;
			int t1 = x1;
			x1 = y1;
			y1 = t1;
//			swap(x0, y0);
//			swap(x1, y1);
		}
 
		if (x0 > x1) {
			int xT = x0;
			x0 = x1;
			x1 = xT;
			int yT = y0;
			y0 = y1;
			y1 = yT;
//			swap(x0, x1);
//			swap(y0, y1);
		}
									
		int dx = x1 - x0;
		int dy = y1 - y0;
		float gradient = (float) dy / (float) dx; //TODO: float?
										
		// handle first endpoint
		float xend = Round(x0);
		float yend = y0 + gradient * (xend - x0);
		float xgap = rFractionalPart(x0 + 0.5f);
		int xpxl1 = Mathf.RoundToInt(xend);   //this will be used in the main loop
		int ypxl1 = Mathf.RoundToInt(IntegerPart(yend));
 
		if(steep) {
			Plot(ypxl1,   xpxl1, rFractionalPart(yend) * xgap, col);
			Plot(ypxl1+1, xpxl1,  FractionalPart(yend) * xgap, col);
		} else {
			Plot(xpxl1, ypxl1  , rFractionalPart(yend) * xgap, col);
			Plot(xpxl1, ypxl1+1,  FractionalPart(yend) * xgap, col);
		}
 
		float intery = yend + gradient; // first y-intersection for the main loop
																
		// handle second endpoint
																
		xend = Round(x1);
		yend = y1 + gradient * (xend - x1);
		xgap = FractionalPart(x1 + 0.5f);
		int xpxl2 = Mathf.RoundToInt(xend); //this will be used in the main loop
		int ypxl2 = Mathf.RoundToInt(IntegerPart(yend));
 
		if (steep) {
			Plot(ypxl2  , xpxl2, rFractionalPart(yend) * xgap, col);
			Plot(ypxl2+1, xpxl2,  FractionalPart(yend) * xgap, col);
		} else {
			Plot(xpxl2, ypxl2,  rFractionalPart(yend) * xgap, col);
			Plot(xpxl2, ypxl2+1, FractionalPart(yend) * xgap, col);
		}
																					
		// main loop
																					
		for (int x = xpxl1 + 1; x < xpxl2 - 1; x++) { //for x from xpxl1 + 1 to xpxl2 - 1 do
	
			if (steep) {
				Plot(Mathf.RoundToInt(IntegerPart(intery))  , x, rFractionalPart(intery), col);
				Plot(Mathf.RoundToInt(IntegerPart(intery)+1f), x,  FractionalPart(intery), col);
			} else {
				Plot(x, Mathf.RoundToInt(IntegerPart (intery)),  rFractionalPart(intery), col);
				Plot(x, Mathf.RoundToInt(IntegerPart (intery)+1), FractionalPart(intery), col);
			}
			intery = intery + gradient;
									
		}
	}
 
	void DrawAALineFloats(float x0, float y0, float x1, float y1, Color col) { //NEWEST. USE THIS!
		
		//TEMP TEST: draw point at beginning and end
		Plot(x0, y0, 1f, col);
		Plot(x1, y1, 1f, col);
		
		bool steep = Mathf.Abs(y1 - y0) > Mathf.Abs(x1 - x0);
		
		if (steep) {
			float t0 = x0;
			x0 = y0;
			y0 = t0;
			float t1 = x1;
			x1 = y1;
			y1 = t1;
			//			swap(x0, y0);
			//			swap(x1, y1);
		}
		
		if (x0 > x1) {
			float xT = x0;
			x0 = x1;
			x1 = xT;
			float yT = y0;
			y0 = y1;
			y1 = yT;
			//			swap(x0, x1);
			//			swap(y0, y1);
		}
		
		float dx = x1 - x0;
		float dy = y1 - y0;
		float gradient = dy / dx; //TODO: float?
		
		// handle first endpoint
		float xend = Round(x0);
		float yend = y0 + gradient * (xend - x0);
		float xgap = rFractionalPart(x0 + 0.5f);
		float xpxl1 = xend;   //this will be used in the main loop
		float ypxl1 = IntegerPart(yend);
		
		if(steep) {
			Plot(ypxl1,   xpxl1, rFractionalPart(yend) * xgap, col);
			Plot(ypxl1+1, xpxl1,  FractionalPart(yend) * xgap, col);
		} else {
			Plot(xpxl1, ypxl1  , rFractionalPart(yend) * xgap, col);
			Plot(xpxl1, ypxl1+1,  FractionalPart(yend) * xgap, col);
		}
		
		float intery = yend + gradient; // first y-intersection for the main loop
		
		// handle second endpoint
		
		xend = Round(x1);
		yend = y1 + gradient * (xend - x1);
		xgap = FractionalPart(x1 + 0.5f);
		float xpxl2 = xend; //this will be used in the main loop
		float ypxl2 = IntegerPart(yend);
		
		if (steep) {
			Plot(ypxl2  , xpxl2, rFractionalPart(yend) * xgap, col);
			Plot(ypxl2+1, xpxl2,  FractionalPart(yend) * xgap, col);
		} else {
			Plot(xpxl2, ypxl2,  rFractionalPart(yend) * xgap, col);
			Plot(xpxl2, ypxl2+1, FractionalPart(yend) * xgap, col);
		}
		
		// main loop
		
		for (float x = xpxl1 + 1; x < xpxl2 - 1; x++) { //for x from xpxl1 + 1 to xpxl2 - 1 do
			
			if (steep) {
				Plot(IntegerPart(intery)  , x, rFractionalPart(intery), col);
				Plot(IntegerPart(intery)+1f, x,  FractionalPart(intery), col);
			} else {
				Plot(x, IntegerPart (intery),  rFractionalPart(intery), col);
				Plot(x, IntegerPart (intery)+1, FractionalPart(intery), col);
			}
			intery = intery + gradient;
			
		}
	}
	
}

Wasn't really sure which data formats to use, ended up doing one version that takes floats and one that takes ints. The result should be pretty much the same...