#include "StdLib.hlsl"

RWStructuredBuffer<uint4> _WaveformBuffer;
Texture2D<float4> _Source;
SamplerState sampler_Source;

cbuffer name
{
	float4 _Params; // x: source width, y: source height, z: linear, w: histogramResolution
};

#if defined SHADER_API_GLES3
	#define GROUP_SIZE 128
	#define GROUP_SIZE_X 16
	#define GROUP_SIZE_Y 8
#else
	#define GROUP_SIZE 256
	#define GROUP_SIZE_X 16
	#define GROUP_SIZE_Y 16
#endif

half3 LinearToSRGB(half3 c)
{
	half3 sRGBLo = c * 12.92;
	half3 sRGBHi = (PositivePow(c, half3(1.0 / 2.4, 1.0 / 2.4, 1.0 / 2.4)) * 1.055) - 0.055;
	half3 sRGB = half3((c.x <= 0.0031308) ? sRGBLo.x : sRGBHi.x, (c.y <= 0.0031308) ? sRGBLo.y : sRGBHi.y, (c.z <= 0.0031308) ? sRGBLo.z : sRGBHi.z);
	return sRGB;
}

#pragma kernel KCMWaveformGather
[numthreads(1, GROUP_SIZE, 1)]
void KCMWaveformGather(uint2 dispatchThreadId : SV_DispatchThreadID)
{
	// Gather local group histogram
	if (dispatchThreadId.x < uint(_Params.x) && dispatchThreadId.y < uint(_Params.y))
	{
		float3 color = _Source[dispatchThreadId].rgb;
		color = saturate(color);

		// We want a gamma-corrected histogram (like Photoshop & all)
		if (_Params.z > 0)
			color = LinearToSRGB(color);

		// Convert channel values to histogram bins
		uint3 idx = (uint3)(round(color * (_Params.w - 1)));
		idx += dispatchThreadId.x * _Params.w;

		if (idx.x > 0u) InterlockedAdd(_WaveformBuffer[idx.x].x, 1u); // Red
		if (idx.y > 0u) InterlockedAdd(_WaveformBuffer[idx.y].y, 1u); // Green
		if (idx.z > 0u) InterlockedAdd(_WaveformBuffer[idx.z].z, 1u); // Blue
	}
}

#pragma kernel KCMWaveformClear
[numthreads(GROUP_SIZE_X, GROUP_SIZE_Y, 1)]
void KCMWaveformClear(uint2 dispatchThreadId : SV_DispatchThreadID)
{
	if (dispatchThreadId.x < uint(_Params.x) && dispatchThreadId.y < uint(_Params.w))
		_WaveformBuffer[dispatchThreadId.y * uint(_Params.x) + dispatchThreadId.x] = uint4(0u, 0u, 0u, 0u);
}