// From: https://github.com/gkjohnson/unity-dithered-transparency-shader
// MIT License

//Copyright (c) 2017 Garrett Johnson

//Permission is hereby granted, free of charge, to any person obtaining a copy
//of this software and associated documentation files (the "Software"), to deal
//in the Software without restriction, including without limitation the rights
//to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//copies of the Software, and to permit persons to whom the Software is
//furnished to do so, subject to the following conditions:

//The above copyright notice and this permission notice shall be included in all
//copies or substantial portions of the Software.

//THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//SOFTWARE.

#ifndef __DITHER_FUNCTIONS__
#define __DITHER_FUNCTIONS__
#include "UnityCG.cginc"

// Returns > 0 if not clipped, < 0 if clipped based
// on the dither
// For use with the "clip" function
// pos is the fragment position in screen space from [0,1]
float isDithered(float2 pos, float alpha) {
    pos *= _ScreenParams.xy;

    // Define a dither threshold matrix which can
    // be used to define how a 4x4 set of pixels
    // will be dithered
    float DITHER_THRESHOLDS[16] =
    {
        1.0 / 17.0,  9.0 / 17.0,  3.0 / 17.0, 11.0 / 17.0,
        13.0 / 17.0,  5.0 / 17.0, 15.0 / 17.0,  7.0 / 17.0,
        4.0 / 17.0, 12.0 / 17.0,  2.0 / 17.0, 10.0 / 17.0,
        16.0 / 17.0,  8.0 / 17.0, 14.0 / 17.0,  6.0 / 17.0
    };

    uint index = (uint(pos.x) % 4) * 4 + uint(pos.y) % 4;
    return alpha - DITHER_THRESHOLDS[index];
}

// Returns whether the pixel should be discarded based
// on the dither texture
// pos is the fragment position in screen space from [0,1]
float isDithered(float2 pos, float alpha, sampler2D tex, float scale) {
    pos *= _ScreenParams.xy;

    // offset so we're centered
    pos.x -= _ScreenParams.x / 2;
    pos.y -= _ScreenParams.y / 2;
    
    // scale the texture
    pos.x /= scale;
    pos.y /= scale;

	// ensure that we clip if the alpha is zero by
	// subtracting a small value when alpha == 0, because
	// the clip function only clips when < 0
    return alpha - tex2D(tex, pos.xy).r - 0.0001 * (1 - ceil(alpha));
}

// Helpers that call the above functions and clip if necessary
void ditherClip(float2 pos, float alpha) {
    clip(isDithered(pos, alpha));
}


sampler2D _BlueNoiseCrossfade;
float4 _BlueNoiseCrossfade_TexelSize;

float rand(float2 co){
    return frac(sin(dot(co.xy ,float2(12.9898,78.233))) * 43758.5453);
}

void ditherClip(float2 pos, float alpha, float clipV) {
	pos *= _ScreenParams.xy;

	//clip(isDithered(pos, alpha));

	float2 vpos = float2((pos.x + pos.y), alpha);
    clip(tex2D(_BlueNoiseCrossfade, vpos).r - clipV);
}

void ditherClip(float2 pos, float alpha, sampler2D tex, float scale) {
    clip(isDithered(pos, alpha, tex, scale));
}
#endif