c# - Monogame shader not working

I'm trying to use this this tutorial in monogame, but the effect does not work, only renders a black screen. Everyhing by itself renders just fine, I looked at the render targets if they get drawn to, but when I try to apply the effect to them it only renders a black screen.

I converted the .fx file using 2MGFX, also tried loading it with the following code:

BinaryReader Reader = new BinaryReader(File.Open(@"Content\\Lighting.mgfx", FileMode.Open));
        lightingEffect = new Effect(GraphicsDevice, Reader.ReadBytes((int)Reader.BaseStream.Length)); 

also with

lightingEffect = content.Load("Lighting.mgfx");

and also with

byte[] bytecode = File.ReadAllBytes("Content\\Lighting.mgfx");
        lightingEffect = new Effect(graphics.GraphicsDevice, bytecode);

They did not make a difference.

The .fx file contains the following:

sampler s0;
texture lightMask;

sampler lightSampler = sampler_state { Texture = ; };

float4 PixelShaderFunction(float2 coords: TEXCOORD0) : COLOR0
{
    float4 color = tex2D(s0, coords);
    float4 lightColor = tex2D(lightSampler, coords);
    return color * lightColor;
}

technique Technique1

{
    pass Pass1
    {
        PixelShader = compile ps_4_0_level_9_1 PixelShaderFunction();
    }
}

And the monogame version of the game1.cs(Only the important stuff):

public class Game1 : Game
{

    GraphicsDeviceManager graphics;
    SpriteBatch spriteBatch;

    Texture2D lightMask;
    Texture2D SquareGuy;

    RenderTarget2D lightsTarget;
    RenderTarget2D mainTarget;

    Effect lightingEffect;



    public Game1()
    {
        graphics = new GraphicsDeviceManager(this);
        Content.RootDirectory = "Content";
        IsMouseVisible = true;
    }



     protected override void LoadContent()
     {
        spriteBatch = new SpriteBatch(GraphicsDevice);
        lightMask = Content.Load("lightmask");
        SquareGuy = Content.Load("SquareGuy");
        // lightingEffect = content.Load("Lighting.mgfx");
        /*
        byte[] bytecode = File.ReadAllBytes("Content\\Lighting.mgfx");
        lightingEffect = new Effect(graphics.GraphicsDevice, bytecode);
        */

        BinaryReader Reader = new     BinaryReader(File.Open(@"Content\\Lighting.mgfx", FileMode.Open));
        lightingEffect = new Effect(GraphicsDevice,     Reader.ReadBytes((int)Reader.BaseStream.Length)); 

        var pp = GraphicsDevice.PresentationParameters;
     //   pp.BackBufferHeight = 1024;
     //   pp.BackBufferWidth = 1024;
        lightsTarget = new RenderTarget2D(
            GraphicsDevice, pp.BackBufferWidth, pp.BackBufferHeight);
        mainTarget = new RenderTarget2D(
            GraphicsDevice, pp.BackBufferWidth, pp.BackBufferHeight);                            

     }          

     protected override void Draw(GameTime gameTime)
     {
        GraphicsDevice.Clear(Color.CornflowerBlue);

        // TODO: Add your drawing code here
        GraphicsDevice.SetRenderTarget(lightsTarget);
        GraphicsDevice.Clear(Color.Black);
        spriteBatch.Begin(SpriteSortMode.Immediate, BlendState.Additive);

        spriteBatch.Draw(lightMask, new Vector2(0, 0), Color.White);
        spriteBatch.Draw(lightMask, new Vector2(100, 0), Color.White);
        spriteBatch.Draw(lightMask, new Vector2(200, 200), Color.White);
        spriteBatch.Draw(lightMask, new Vector2(300, 300), Color.White);
        spriteBatch.Draw(lightMask, new Vector2(500, 200), Color.White);
        spriteBatch.End();

        // Draw the main scene to the Render Target
        GraphicsDevice.SetRenderTarget(mainTarget);
        GraphicsDevice.Clear(Color.CornflowerBlue);

        spriteBatch.Begin();
        spriteBatch.Draw(SquareGuy, new Vector2(100, 0), Color.White);
        spriteBatch.Draw(SquareGuy, new Vector2(250, 250), Color.White);
        spriteBatch.Draw(SquareGuy, new Vector2(550, 225), Color.White);
        spriteBatch.End();

        // Draw the main scene with a pixel
        GraphicsDevice.SetRenderTarget(null);
        GraphicsDevice.Clear(Color.CornflowerBlue);
        spriteBatch.Begin(SpriteSortMode.Immediate, BlendState.AlphaBlend);

        lightingEffect.Parameters["lightMask"].SetValue(lightsTarget);
        lightingEffect.CurrentTechnique.Passes[0].Apply();
        spriteBatch.Draw(mainTarget, Vector2.Zero, Color.White);
        spriteBatch.End();

        base.Draw(gameTime);
    }
}

So the question is what do I need to change to make the effect work in monogame?

I tried it in XNA with this code and worked perfectly. I know almost nothing about HLSL, so I don't know if theres something wrong with the effect. I only changed the version thingy from ps_2_0 to ps_4_0_level_9_1. If I change it to ps_4_0_level_9_3 it still doesn't work. I read something about assigning textures from outside of the .fx here, but since I know so little about shaders I don't know if this is the problem.

Answer

I had this same problem last week. You need to add all the parameters to your PixelShaderFunction, or monogame will map registers incorrectly. Change your PixelShaderFunction parameters to be like this:

PixelShaderFunction(float4 pos : SV_POSITION, float4 color1 : COLOR0, float2 coords: TEXCOORD0)

Here is a more detailed explanation, where I got the answer: http://www.software7.com/blog/pitfalls-when-developing-hlsl-shader/