// Copyright (C) 2009-present, Panagiotis Christopoulos Charitos and contributors.
// All rights reserved.
// Code licensed under the BSD License.
// http://www.anki3d.org/LICENSE

#include <AnKi/Shaders/Functions.hlsl>

#pragma anki technique comp

Texture2D<Vec4> g_depthRt : register(t0);
SamplerState g_linearAnyClampSampler : register(s0);
RWTexture2D<Vec4> g_maxDepthStorageTex : register(u0);

#define TILE_SIZE 64
#define THREADGROUP_SIZE_XY 32
#define MIN_POSSIBLE_WAVE_SIZE 8

groupshared U32 s_maxDepth;

[numthreads(THREADGROUP_SIZE_XY, THREADGROUP_SIZE_XY, 1)] void main(UVec2 svGroupThreadId : SV_GROUPTHREADID, UVec2 svGroupId : SV_GROUPID,
																	U32 svGroupIndex : SV_GROUPINDEX)
{
	if(svGroupIndex == 0)
	{
		s_maxDepth = 0;
	}

	GroupMemoryBarrierWithGroupSync();

	Vec2 depthRtSize;
	g_depthRt.GetDimensions(depthRtSize.x, depthRtSize.y);

	const Vec2 uv = Vec2(svGroupId * TILE_SIZE + svGroupThreadId * 2u + 1u) / depthRtSize;

	const Vec4 depths = g_depthRt.GatherRed(g_linearAnyClampSampler, uv);

	const F32 maxDepth = max4(depths);
	const U32 maxDepthu = asuint(maxDepth);

	InterlockedMax(s_maxDepth, maxDepthu);

	GroupMemoryBarrierWithGroupSync();

	if(svGroupIndex == 0)
	{
		g_maxDepthStorageTex[svGroupId] = asfloat(s_maxDepth);
	}
}