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eac.glsl
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eac.glsl
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#version 430 core
// Define this to use the compressor to generate data for R11 (or RG11)
// Without defining this, the compressor generates data for ETC2_Alpha
// It's almost the same but there are subtle differences
// (they differ on how multiplier = 0 is handled. ETC2_Alpha just forbids it; also
// due to their 8-bit and 11-bit differences, in Alpha mode we can take a shorcut
// if all pixels in the block are of the same value)
// #define R11_EAC
#ifndef R11_EAC
// Ballot & group vote are both used as optimization (both must be present or none)
// We have a fallback path if it's not supported
# extension GL_ARB_shader_ballot : enable
# extension GL_ARB_shader_group_vote : enable
# ifdef GL_ARB_shader_ballot
# ifdef GL_ARB_shader_group_vote
# define WARP_SYNC_AVAILABLE
# endif
# endif
#endif
// #include "/media/matias/Datos/SyntaxHighlightingMisc.h"
#include "CrossPlatformSettings_piece_all.glsl"
#include "UavCrossPlatform_piece_all.glsl"
#define FLT_MAX 340282346638528859811704183484516925440.0f
#define PotentialSolution uint
#ifdef R11_EAC
# define EAC_FETCH_SWIZZLE r
# define EAC_RANGE 2047.0f
# define EAC_MULTIPLIER_START 0u
#else
# define EAC_FETCH_SWIZZLE a
# define EAC_RANGE 255.0f
# define EAC_MULTIPLIER_START 1u
#endif
PotentialSolution storePotentialSolution( const float baseCodeword, const int tableIdx,
const float multiplier )
{
return packUnorm4x8( float4( baseCodeword, float( tableIdx ), multiplier, 0.0f ) *
( 1.0f / 255.0f ) );
}
void loadPotentialSolution( PotentialSolution potentialSolution, out float baseCodeword,
out uint tableIdx, out float multiplier )
{
const float4 val = unpackUnorm4x8( potentialSolution );
baseCodeword = val.x * 255.0f;
tableIdx = uint( val.y * 255.0f );
multiplier = val.z * 255.0f;
}
// For alpha support
const float kEacModifiers[16][8] = { //
{ -3, -6, -9, -15, 2, 5, 8, 14 }, //
{ -3, -7, -10, -13, 2, 6, 9, 12 }, //
{ -2, -5, -8, -13, 1, 4, 7, 12 }, //
{ -2, -4, -6, -13, 1, 3, 5, 12 }, //
{ -3, -6, -8, -12, 2, 5, 7, 11 }, //
{ -3, -7, -9, -11, 2, 6, 8, 10 }, //
{ -4, -7, -8, -11, 3, 6, 7, 10 }, //
{ -3, -5, -8, -11, 2, 4, 7, 10 }, //
{ -2, -6, -8, -10, 1, 5, 7, 9 }, //
{ -2, -5, -8, -10, 1, 4, 7, 9 }, //
{ -2, -4, -8, -10, 1, 3, 7, 9 }, //
{ -2, -5, -7, -10, 1, 4, 6, 9 }, //
{ -3, -4, -7, -10, 2, 3, 6, 9 }, //
{ -1, -2, -3, -10, 0, 1, 2, 9 }, //
{ -4, -6, -8, -9, 3, 5, 7, 8 }, //
{ -3, -5, -7, -9, 2, 4, 6, 8 }
};
// 2 sets of 16 float3 (rgba8_unorm) for each ETC block
// We use rgba8_unorm encoding because it's 6kb vs 1.5kb of LDS. The former kills occupancy
shared float g_srcPixelsBlock[16];
shared PotentialSolution g_bestSolution[256];
shared float g_bestError[256];
#ifndef R11_EAC
shared bool g_allPixelsEqual;
layout( location = 0 ) uniform float p_greenChannel;
#endif
uniform sampler2D srcTex;
layout( rg32ui ) uniform restrict writeonly uimage2D dstTexture;
layout( local_size_x = 256, //
local_size_y = 1, //
local_size_z = 1 ) in;
float calcError( float3 a, float3 b )
{
float3 diff = a - b;
return dot( diff, diff );
}
float eac_find_best_error( float baseCodeword, float multiplier, const int tableIdx )
{
float accumError = 0.0f;
#ifdef R11_EAC
baseCodeword = baseCodeword * 8.0f + 4.0f;
multiplier = multiplier > 0.0f ? multiplier * 8.0f : 1.0f;
#endif
for( int i = 0; i < 16; ++i )
{
const float realV = g_srcPixelsBlock[i];
float bestError = FLT_MAX;
// Find modifier index through brute force
for( int j = 0; j < 8 && bestError > 0; ++j )
{
const float tryValue =
clamp( baseCodeword + kEacModifiers[tableIdx][j] * multiplier, 0.0f, EAC_RANGE );
const float error = abs( realV - tryValue );
if( error < bestError )
bestError = error;
}
accumError += bestError * bestError;
}
return accumError;
}
void eac_pack( float baseCodeword, float multiplier, const uint tableIdx )
{
const uint iBaseCodeword = uint( baseCodeword );
const uint iMultiplier = uint( multiplier );
#ifdef R11_EAC
baseCodeword = baseCodeword * 8.0f + 4.0f;
multiplier = multiplier > 0.0f ? multiplier * 8.0f : 1.0f;
#endif
uint bestIdx[16];
for( int i = 0; i < 16; ++i )
{
const float realV = g_srcPixelsBlock[i];
float bestError = FLT_MAX;
// Find modifier index through brute force
for( uint j = 0u; j < 8u && bestError > 0; ++j )
{
const float tryValue =
clamp( baseCodeword + kEacModifiers[tableIdx][j] * multiplier, 0.0f, EAC_RANGE );
const float error = abs( realV - tryValue );
if( error < bestError )
{
bestError = error;
bestIdx[i] = j;
}
}
}
uint2 outputBytes;
// Bits [0; 16)
outputBytes.x = iBaseCodeword | ( tableIdx << 8u ) | ( iMultiplier << 12u );
// Bits [16; 24)
outputBytes.x |= ( bestIdx[0] << 21u ) | ( bestIdx[1] << 18u ) | ( ( bestIdx[2] & 0x06u ) << 15u );
// Bits [24; 32)
outputBytes.x |= ( ( bestIdx[2] & 0x01u ) << 31u ) | ( bestIdx[3] << 28u ) | ( bestIdx[4] << 25u ) |
( ( bestIdx[5] & 0x04u ) << 22u );
// Bits [0; 8)
outputBytes.y = ( ( bestIdx[5] & 0x03u ) << 6u ) | ( bestIdx[6] << 3u ) | bestIdx[7];
// Bits [8; 16)
outputBytes.y |= ( bestIdx[8] << 13u ) | ( bestIdx[9] << 10u ) | ( ( bestIdx[10] & 0x06u ) << 7u );
// Bits [16; 24)
outputBytes.y |= ( ( bestIdx[10] & 0x01u ) << 23u ) | ( bestIdx[11] << 20u ) |
( bestIdx[12] << 17u ) | ( ( bestIdx[13] & 0x04u ) << 14u );
// Bits [24; 32)
outputBytes.y |=
( ( bestIdx[13] & 0x03u ) << 30u ) | ( bestIdx[14] << 27u ) | ( bestIdx[15] << 24u );
const uint2 dstUV = gl_WorkGroupID.xy;
imageStore( dstTexture, int2( dstUV ), uint4( outputBytes.xy, 0u, 0u ) );
}
void main()
{
// We perform a brute force search:
//
// 256 base codewords
// 16 table indices
// 16 multipliers
// 8 possible indices per pixel (16 pixels)
//
// That means we have to try 256*16*16*(8*16) = 8.388.608 variations per block
const uint baseCodeword = gl_LocalInvocationID.x;
// Load all pixels. We have 256 threads so have the first 16 load 1 pixel each
if( baseCodeword < 16u )
{
uint2 pixelToLoad = gl_WorkGroupID.xy << 2u;
// Note EAC wants the src pixels transposed!
pixelToLoad.x += baseCodeword >> 2u; //+= baseCodeword / 4
pixelToLoad.y += baseCodeword & 0x03u; //+= baseCodeword % 4
#ifdef R11_EAC
float2 value = OGRE_Load2D( srcTex, int2( pixelToLoad ), 0 ).rg;
const float srcPixel = p_greenChannel != 0 ? value.g : value.r;
#else
const float srcPixel = OGRE_Load2D( srcTex, int2( pixelToLoad ), 0 ).a;
#endif
#ifdef WARP_SYNC_AVAILABLE
if( gl_SubGroupSizeARB >= 16u )
{
// Check if all pixels are equal (when wavefront optimizations are possible)
const bool bSameValue = readFirstInvocationARB( srcPixel ) == srcPixel;
const bool allPixelsEqual = allInvocationsARB( bSameValue );
if( baseCodeword == 0u )
g_allPixelsEqual = allPixelsEqual;
}
#endif
g_srcPixelsBlock[baseCodeword] = srcPixel * EAC_RANGE;
}
#ifndef R11_EAC
# ifdef WARP_SYNC_AVAILABLE
if( gl_SubGroupSizeARB < 16u )
# endif
{
// Fallback path when shader ballot cannot be used (wavefront size too small)
// Check if all pixels are equal
__sharedOnlyBarrier;
bool allPixelsEqual = true;
for( uint i = 1u; i < 16u; ++i )
{
if( g_srcPixelsBlock[0] != g_srcPixelsBlock[i] )
allPixelsEqual = false;
}
g_allPixelsEqual = allPixelsEqual;
}
#endif
__sharedOnlyBarrier;
#ifndef R11_EAC
// In alpha mode, the baseCodeword can represent all 255 values exactly.
// In R11 mode, the 8-bit baseCodeword gets converted to 11 bits, and
// added to the modifier from the table thus we can't take the shortcut
if( g_allPixelsEqual )
{
if( baseCodeword == 0u )
{
uint2 outputBytes;
outputBytes.x = uint( ( g_srcPixelsBlock[0] / EAC_RANGE ) * 255.0f );
outputBytes.y = 0u;
const uint2 dstUV = gl_WorkGroupID.xy;
imageStore( dstTexture, int2( dstUV ), uint4( outputBytes.xy, 0u, 0u ) );
}
}
else
#endif
{
float bestError = FLT_MAX;
PotentialSolution bestSolution = 0u;
const float fBaseCodeword = float( baseCodeword );
for( int tableIdx = 0; tableIdx < 16; ++tableIdx )
{
for( float multiplier = EAC_MULTIPLIER_START; multiplier < 16; ++multiplier )
{
const float error = eac_find_best_error( fBaseCodeword, multiplier, tableIdx );
if( error < bestError )
{
bestError = error;
bestSolution = storePotentialSolution( fBaseCodeword, tableIdx, multiplier );
}
}
}
g_bestError[baseCodeword] = bestError;
g_bestSolution[baseCodeword] = bestSolution;
__sharedOnlyBarrier;
// Parallel reduction to find the best solution
const uint iterations = 8u; // 256 threads = 256 reductions = 2⁸ -> 8 iterations
for( uint i = 0u; i < iterations; ++i )
{
const uint mask = ( 1u << ( i + 1u ) ) - 1u;
const uint idx = 1u << i;
if( ( baseCodeword & mask ) == 0u )
{
if( g_bestError[baseCodeword + idx] < bestError )
{
bestError = g_bestError[baseCodeword + idx];
g_bestError[baseCodeword] = bestError;
g_bestSolution[baseCodeword] = g_bestSolution[baseCodeword + idx];
}
}
__sharedOnlyBarrier;
}
if( baseCodeword == 0u )
{
float bestBaseCodeword, bestMultiplier;
uint bestTableIdx;
loadPotentialSolution( g_bestSolution[0u], bestBaseCodeword, bestTableIdx, bestMultiplier );
eac_pack( bestBaseCodeword, bestMultiplier, bestTableIdx );
}
}
}