libSquish/singlecolourfit.cpp

/* -----------------------------------------------------------------------------

	Copyright (c) 2006 Simon Brown                          si@sjbrown.co.uk

	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.
	
   -------------------------------------------------------------------------- */
   
#include "singlecolourfit.h"
#include "colourset.h"
#include "colourblock.h"
#include "colourblockGCN.h"

namespace squish {

struct SourceBlock
{
	u8 start;
	u8 end;
	u8 error;
};

struct SingleColourLookup
{
	SourceBlock sources[2];
};

#include "singlecolourlookup.inl"

static int FloatToInt( float a, int limit )
{
	// use ANSI round-to-zero behaviour to get round-to-nearest
	int i = ( int )( a + 0.5f );

	// clamp to the limit
	if( i < 0 )
		i = 0;
	else if( i > limit )
		i = limit; 

	// done
	return i;
}

SingleColourFit::SingleColourFit( ColourSet const* colours, int flags )
  : ColourFit( colours, flags )
{
	// grab the single colour
	Vec3 const* values = m_colours->GetPoints();
	m_colour[0] = ( u8 )FloatToInt( 255.0f*values->X(), 255 );
	m_colour[1] = ( u8 )FloatToInt( 255.0f*values->Y(), 255 );
	m_colour[2] = ( u8 )FloatToInt( 255.0f*values->Z(), 255 );
		
	// initialise the best error
	m_besterror = INT_MAX;
}

void SingleColourFit::Compress3( void* block )
{
	// build the table of lookups
	SingleColourLookup const* const lookups[] = 
	{
		lookup_5_3, 
		lookup_6_3, 
		lookup_5_3
	};
	
	// find the best end-points and index
	ComputeEndPoints( lookups );
	
	// build the block if we win
	if( m_error < m_besterror )
	{
		// remap the indices
		u8 indices[16];
		m_colours->RemapIndices( &m_index, indices );
		
		// save the block
		if ( ( m_flags & kDxt1GCN ) != 0 )
			WriteColourBlock3GCN( m_start, m_end, indices, block );
		else
			WriteColourBlock3( m_start, m_end, indices, block );

		// save the error
		m_besterror = m_error;
	}
}

void SingleColourFit::Compress4( void* block )
{
	// build the table of lookups
	SingleColourLookup const* const lookups[] = 
	{
		lookup_5_4, 
		lookup_6_4, 
		lookup_5_4
	};
	
	// find the best end-points and index
	ComputeEndPoints( lookups );
	
	// build the block if we win
	if( m_error < m_besterror )
	{
		// remap the indices
		u8 indices[16];
		m_colours->RemapIndices( &m_index, indices );
		
		// save the block
		if ( ( m_flags & kDxt1GCN ) != 0 )
			WriteColourBlock4GCN( m_start, m_end, indices, block );
		else
			WriteColourBlock4( m_start, m_end, indices, block );

		// save the error
		m_besterror = m_error;
	}
}

void SingleColourFit::ComputeEndPoints( SingleColourLookup const* const* lookups )
{
	// check each index combination (endpoint or intermediate)
	m_error = INT_MAX;
	for( int index = 0; index < 2; ++index )
	{
		// check the error for this codebook index
		SourceBlock const* sources[3];
		int error = 0;
		for( int channel = 0; channel < 3; ++channel )
		{
			// grab the lookup table and index for this channel
			SingleColourLookup const* lookup = lookups[channel];
			int target = m_colour[channel];
			
			// store a pointer to the source for this channel
			sources[channel] = lookup[target].sources + index;
			
			// accumulate the error
			int diff = sources[channel]->error;
			error += diff*diff;			
		}
		
		// keep it if the error is lower
		if( error < m_error )
		{
			m_start = Vec3(
				( float )sources[0]->start/31.0f, 
				( float )sources[1]->start/63.0f, 
				( float )sources[2]->start/31.0f
			);
			m_end = Vec3(
				( float )sources[0]->end/31.0f, 
				( float )sources[1]->end/63.0f, 
				( float )sources[2]->end/31.0f
			);
			m_index = ( u8 )( 2*index );
			m_error = error;
		}
	}
}

} // namespace squish