source-engine/bitmap/float_bm2.cpp

//========= Copyright Valve Corporation, All rights reserved. ============//
//
// Purpose: 
//
//===========================================================================//

#include <tier0/platform.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
#include "bitmap/float_bm.h"


static float ScaleValue(float f, float overbright)
{
	// map a value between 0..255 to the scale factor
	int ival=f;
	return ival*(overbright/255.0);
}

static float IScaleValue(float f, float overbright)
{
	f*=(1.0/overbright);
	int ival=min(255,(int)ceil(f*255.0));
	return ival;
}

void MaybeSetScaleVaue(FloatBitMap_t const &orig, FloatBitMap_t &newbm, int x, int y, 
					   float newscale, float overbright)
{
	// clamp the given scale value to the legal range for that pixel and regnerate the rgb
	// components.
	float maxc=max(max(orig.Pixel(x,y,0),orig.Pixel(x,y,1)),orig.Pixel(x,y,2));
	if (maxc==0.0)
	{
		// pixel is black. any scale value is fine.
		newbm.Pixel(x,y,3)=newscale;
		for(int c=0;c<3;c++)
			newbm.Pixel(x,y,c)=0;
	}
	else
	{
//		float desired_floatscale=maxc;
		float scale_we_will_get=ScaleValue(newscale,overbright);
//		if (scale_we_will_get >= desired_floatscale )
		{
			newbm.Pixel(x,y,3)=newscale;
			for(int c=0;c<3;c++)
				newbm.Pixel(x,y,c)=orig.Pixel(x,y,c)/(scale_we_will_get);
		}
	}
}


void FloatBitMap_t::Uncompress(float overbright)
{
	for(int y=0;y<Height;y++)
		for(int x=0;x<Width;x++)
		{
			int iactual_alpha_value=255.0*Pixel(x,y,3);
			float actual_alpha_value=iactual_alpha_value*(1.0/255.0);
			for(int c=0;c<3;c++)
			{
				int iactual_color_value=255.0*Pixel(x,y,c);
				float actual_color_value=iactual_color_value*(1.0/255.0);
				Pixel(x,y,c)=actual_alpha_value*actual_color_value*overbright;
			}
		}
}

#define GAUSSIAN_WIDTH 5
#define SQ(x) ((x)*(x))

void FloatBitMap_t::CompressTo8Bits(float overbright)
{
	FloatBitMap_t TmpFBM(Width,Height);
	// first, saturate to max overbright
	for(int y=0;y<Height;y++)
		for(int x=0;x<Width;x++)
			for(int c=0;c<3;c++)
				Pixel(x,y,c)=min(overbright,Pixel(x,y,c));
	// first pass - choose nominal scale values to convert to rgb,scale
	for(int y=0;y<Height;y++)
		for(int x=0;x<Width;x++)
		{
			// determine maximum component
			float maxc=max(max(Pixel(x,y,0),Pixel(x,y,1)),Pixel(x,y,2));
			if (maxc==0)
			{
				for(int c=0;c<4;c++)
					TmpFBM.Pixel(x,y,c)=0;
			}
			else
			{
				float desired_floatscale=maxc;
				float closest_iscale=IScaleValue(desired_floatscale, overbright);
				float scale_value_we_got=ScaleValue(closest_iscale, overbright );
				TmpFBM.Pixel(x,y,3)=closest_iscale;
				for(int c=0;c<3;c++)
					TmpFBM.Pixel(x,y,c)=Pixel(x,y,c)/scale_value_we_got;
			}
		}
	// now, refine scale values
#ifdef FILTER_TO_REDUCE_LERP_ARTIFACTS
// I haven't been able to come up with a filter which eleiminates objectionable artifacts on all
// source textures. So, I've gone to doing the lerping in the shader.
	int pass=0;
	while(pass<1)
	{
		FloatBitMap_t temp_filtered(&TmpFBM);
		for(int y=0;y<Height;y++)
		{
			for(int x=0;x<Width;x++)
			{
				float sum_scales=0.0;
				float sum_weights=0.0;
				for(int yofs=-GAUSSIAN_WIDTH;yofs<=GAUSSIAN_WIDTH;yofs++)
					for(int xofs=-GAUSSIAN_WIDTH;xofs<=GAUSSIAN_WIDTH;xofs++)
					{
						float r=0.456*GAUSSIAN_WIDTH;
						r=0.26*GAUSSIAN_WIDTH;
						float x1=xofs/r;
						float y1=yofs/r;
						float a=(SQ(x1)+SQ(y1))/(2.0*SQ(r));
						float w=exp(-a);
						sum_scales+=w*TmpFBM.PixelClamped(x+xofs,y+yofs,3);
						sum_weights+=w;
					}
				int new_trial_scale=sum_scales*(1.0/sum_weights);
				MaybeSetScaleVaue(*this,temp_filtered,x,y,new_trial_scale,overbright);
			}
		}
		pass++;
		memcpy(TmpFBM.RGBAData,temp_filtered.RGBAData,Width*Height*4*sizeof(float));
	}
#endif

	memcpy(RGBAData,TmpFBM.RGBAData,Width*Height*4*sizeof(float));
	// now, map scale to real value
	for(int y=0;y<Height;y++)
		for(int x=0;x<Width;x++)
			Pixel(x,y,3)*=(1.0/255.0);
}