anki-3d-engine/AnKi/Shaders/TonemappingAverageLuminance.ankiprog

// Copyright (C) 2009-2021, Panagiotis Christopoulos Charitos and contributors.
// All rights reserved.
// Code licensed under the BSD License.
// http://www.anki3d.org/LICENSE

ANKI_SPECIALIZATION_CONSTANT_UVEC2(INPUT_TEX_SIZE, 0u);

#pragma anki start comp
#define LOG_AVG 0

#include <AnKi/Shaders/TonemappingFunctions.glsl>

const UVec2 WORKGROUP_SIZE = UVec2(32u, 16u);
layout(local_size_x = WORKGROUP_SIZE.x, local_size_y = WORKGROUP_SIZE.y, local_size_z = 1) in;

// Align the tex size to workgroup size
const UVec2 ALIGNED_INPUT_TEX_SIZE = WORKGROUP_SIZE * ((INPUT_TEX_SIZE + WORKGROUP_SIZE - 1u) / WORKGROUP_SIZE);
const UVec2 PIXELS_PER_TILE = ALIGNED_INPUT_TEX_SIZE / WORKGROUP_SIZE;

layout(set = 0, binding = 0) uniform texture2D u_tex;

#define TONEMAPPING_RESOURCE_AS_BUFFER 1
#define TONEMAPPING_SET 0
#define TONEMAPPING_BINDING 1
#include <AnKi/Shaders/TonemappingResources.glsl>

shared F32 s_avgLum[WORKGROUP_SIZE.x * WORKGROUP_SIZE.y];

void main()
{
	// Gather the log-average luminance of a tile. It will miss some pixels but not too many
	const U32 yStart = gl_LocalInvocationID.y * PIXELS_PER_TILE.y;
	const U32 xStart = gl_LocalInvocationID.x * PIXELS_PER_TILE.x;

	F32 avgLum = 0.0;
	ANKI_UNROLL for(U32 y = 0u; y < PIXELS_PER_TILE.y; ++y)
	{
		ANKI_UNROLL for(U32 x = 0u; x < PIXELS_PER_TILE.x; ++x)
		{
			const UVec2 uv = UVec2(xStart, yStart) + UVec2(x, y);
			if(uv.x >= INPUT_TEX_SIZE.x || uv.y >= INPUT_TEX_SIZE.y)
			{
				continue;
			}

			const Vec3 color = texelFetch(u_tex, IVec2(uv), 0).rgb;
			const F32 lum = computeLuminance(color);
#if LOG_AVG
			avgLum += log(max(EPSILON, lum));
#else
			avgLum += lum;
#endif
		}
	}

	s_avgLum[gl_LocalInvocationIndex] = avgLum;

	memoryBarrierShared();
	barrier();

	// Gather the results into one
	ANKI_LOOP for(U32 s = (WORKGROUP_SIZE.x * WORKGROUP_SIZE.y) / 2u; s > 0u; s >>= 1u)
	{
		if(gl_LocalInvocationIndex < s)
		{
			s_avgLum[gl_LocalInvocationIndex] += s_avgLum[gl_LocalInvocationIndex + s];
		}

		memoryBarrierShared();
		barrier();
	}

	// Write the result
	ANKI_BRANCH if(gl_LocalInvocationIndex == 0u)
	{
#if LOG_AVG
		const F32 crntLum = exp(s_avgLum[0] * (1.0 / F32(INPUT_TEX_SIZE.x * INPUT_TEX_SIZE.y)));
#else
		const F32 crntLum = s_avgLum[0] * (1.0 / F32(INPUT_TEX_SIZE.x * INPUT_TEX_SIZE.y));
#endif

#if 1
		const F32 prevLum = u_averageLuminance;

		// Lerp between previous and new L value
		const F32 INTERPOLATION_FACTOR = 0.05;
		F32 finalAvgLum = mix(prevLum, crntLum, INTERPOLATION_FACTOR);
#else
		F32 finalAvgLum = crntLum;
#endif

		// This is a workaround because sometimes the avg lum becomes nan
		finalAvgLum = clamp(finalAvgLum, EPSILON, FLT_MAX);

		u_averageLuminance = finalAvgLum;
		u_exposureThreshold0 = computeExposure(u_averageLuminance, 0.0);
	}
}
#pragma anki end