LÖVE

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--By xXxMoNkEyMaNxXx
--[[Complete API----  This was made to be a module, PLEASE USE IT AS A MODULE

	.cw=false
	-Counter clockwise vertex order starting at top left.

	.cw=true
	-Clockwise vertex order starting at top left.


	.preload(loadup):

	-loadup==true sets pixel effect to polygon texturer,
	-loadup==false clears any pixel effect.
	*NOTE: preload(false) must be done to draw blank polygons after textured ones.


	.setRepeat(origin,size):
	-Makes the image repeat every 'size' starting at 'origin'.
	-The default is origin={0,0},size={1,1}.


	.quad(image,v1,v2,v3,v4) - Draws a polygon.

	-if 'image' is nil, the function will prepare to make it blank.


	.quad(v1,v2,v3,v4) - draws a polygon with no image.


	.fast(image,v1,v2,v3,v4) - draws a polygon with 'image' on it.
	-slightly(!!!) faster than quad.
	-Must include an image.
	-Must call .preload(true) beforehand.


	Info:
	Vertices are in the form {x,y}.
	Vertices go clockwise from the top left.

	v1---v2
	| img |
	v4---v3
--]]

--Modified by RogueCarrot
local glsl=love.graphics.newShader[[
//Made by xXxMoNkEyMaNxXx

extern Image img;
extern vec2 v1;
extern vec2 v2;
extern vec2 v3;
extern vec2 v4;

extern vec2 p0;
extern vec2 rep;

extern number SIZEY;//So annoying
extern number SIZEX;//So annoying

vec2 one=vec2(1.0,1.0);

number c(vec2 v1,vec2 v2)
{
	return v1.x*v2.y-v2.x*v1.y;
}
number intersect(vec2 v1,vec2 d1,vec2 v2,vec2 d2)
{
	//v1+d1*
	return c(v2-v1,d2)/c(d1,d2);
}
vec4 mask(vec4 base,vec4 over)
{
	return vec4(over.rgb*over.a+base.rgb*(1-over.a),over.a+base.a*(1-over.a));
}
vec4 effect(vec4 colour,Image UNUSED1,vec2 UNUSED2,vec2 inverted)
{
	vec2 p=vec2(inverted.x*SIZEX,SIZEY-inverted.y);//SO ANNOYING

	vec2 A1=normalize(v2-v1);
	vec2 A2=normalize(v3-v4);

	vec2 B1=normalize(v2-v3);
	vec2 B2=normalize(v1-v4);

	number Adiv=c(A1,A2);
	number Bdiv=c(B1,B2);

	vec2 uv;

	bvec2 eq0=bvec2(abs(Adiv)<=0.0001,abs(Bdiv)<=0.0001);
	if(eq0.x && eq0.y){
		//Both edges are parallel, therefore the shape is a parallelogram (Isometric)
		number dis=dot(p-v1,A1);

		//cos theta
		number ct=dot(A1,B1);

		//Closest point on v1->A1 to p
		vec2 pA=v1+A1*dis;

		//uv
		number r=length(p-pA)/sqrt(1-ct*ct);
		uv=vec2(1-r/length(v2-v3),(dis+r*ct)/length(v2-v1));
	}else if(eq0.x){
		//One Vanishing point occurs in numerically set scenarios in 3D, and is a feature of 2.5D

		//Horizon is A1 (=A2) from B
		vec2 Vp=v3+B1*c(v4-v3,B2)/Bdiv;

		//Some point in the distance that diagonals go to
		vec2 D=Vp+A1*intersect(Vp,A1,v4,normalize(v2-v4));

		//uv
		number u=intersect(v1,A1,Vp,normalize(p-Vp));
		number v=intersect(v1,A1,D,normalize(p-D))-u;

		number len=length(v2-v1);
		uv=vec2(len-v,u)/len;//Reversed components to match up with other one
	}else if(eq0.y){
		//If the other edge is the parallel one
		vec2 Vp=v1+A1*c(v4-v1,A2)/Adiv;
		vec2 D=Vp+B1*intersect(Vp,B1,v4,normalize(v2-v4));
		number u=intersect(v3,B1,Vp,normalize(p-Vp));
		number len=length(v2-v3);
		uv=vec2(u,len-intersect(v3,B1,D,normalize(p-D))+u)/len;
	}else{
		//Else, two vanishing points

		//*intersect(v1,A1,v4,A2)
		//*intersect(v3,B1,v4,B2)

		//Vanishing points
		vec2 A=v1+A1*c(v4-v1,A2)/Adiv;
		vec2 B=v3+B1*c(v4-v3,B2)/Bdiv;

		//Horizon
		vec2 H=normalize(A-B);

		//Pixel
		uv=vec2(intersect(v4,-H,A,normalize(p-A))/intersect(v4,-H,v2,-A1),intersect(v4,H,B,normalize(p-B))/intersect(v4,H,v2,-B1));
	}
	return mask(colour,Texel(img,mod(uv*rep+vec2(p0.x-1,p0.y),one)));
}
]]
local gl_send=glsl.send
local q=love.graphics.polygon
local win = love.window
-- local lgr = love.graphics
local setEffect=love.graphics.setShader
gl_send(glsl,"SIZEX",1)--So annoying
gl_send(glsl,"SIZEY",love.graphics.getHeight())--So annoying
gl_send(glsl,"p0",{0,0})
gl_send(glsl,"rep",{1,1})

module(...)
cw=true--clockwise
function preload(loadup)
	if loadup then
		setEffect(glsl)
	else
		setEffect()
	end
end
function setRepeat(origin,size)
	gl_send(glsl,"p0",origin)
	gl_send(glsl,"rep",size)
end
function fast(img,v1,v2,v3,v4)
	gl_send(glsl,"img",img)
	gl_send(glsl,"v1",v2)
	gl_send(glsl,"v2",v3)
	gl_send(glsl,"v3",v4)
	gl_send(glsl,"v4",v1)
	q("fill",v1[1],v1[2],v2[1],v2[2],v3[1],v3[2],v4[1],v4[2])
end
function quad(img,v1,v2,v3,v4,w,h)
	if h then gl_send(glsl,"SIZEY",h) end
	if w then gl_send(glsl,"SIZEX",w/win.getWidth()) end
	if img and v4 then
		setEffect(glsl)
		gl_send(glsl,"img",img)
		if cw then
			gl_send(glsl,"v1",v2)
			gl_send(glsl,"v2",v3)
			gl_send(glsl,"v3",v4)
			gl_send(glsl,"v4",v1)
		else
			gl_send(glsl,"v1",v2)
			gl_send(glsl,"v2",v1)
			gl_send(glsl,"v3",v4)
			gl_send(glsl,"v4",v3)
		end
	else
		setEffect()
	end
	if v4 then
		q("fill",v1[1],v1[2],v2[1],v2[2],v3[1],v3[2],v4[1],v4[2])
	else--img acts as a vertex
		q("fill",img[1],img[2],v1[1],v1[2],v2[1],v2[2],v3[1],v3[2])
	end
	setEffect()
end

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vec3 ab_n = cross(n, ab);
vec3 ac_n = cross(n, ac);

float u = dot(pos - a, ab_n) / dot(ac, ab_n);
float v = dot(pos - a, ac_n) / dot(ab, ac_n);

vec2 texCoord = at + (ct - at)*u + (bt - at)*v;
vec4 texColor = texture2D(textureMap, texCoord);