Leaked source code of windows server 2003
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/* COLOR2.C
**
** Copyright (C) Microsoft, 1993, All Rights Reserved.
**
**
** History:
**
*/
#include "priv.h"
int H,L,S; /* Hue, Lightness, Saturation */
#define RANGE 240 /* range of values for HLS scrollbars */
/* HLS-RGB conversions work best when
RANGE is divisible by 6 */
#define HLSMAX RANGE
#define RGBMAX 255
#define MIN(a, b) ((a) < (b) ? (a) : (b))
/* Color conversion routines --
RGBtoHLS() takes a DWORD RGB value, translates it to HLS, and stores the
results in the global vars H, L, and S. HLStoRGB takes the current values
of H, L, and S and returns the equivalent value in an RGB DWORD. The vars
H, L and S are written to only by 1) RGBtoHLS (initialization) or 2) the
scrollbar handlers.
A point of reference for the algorithms is Foley and Van Dam, pp. 618-19.
Their algorithm is in floating point. CHART implements a less general
(hardwired ranges) integral algorithm.
*/
/* There are potential roundoff errors lurking throughout here.
(0.5 + x/y) without floating point,
(x/y) phrased ((x + (y/2))/y)
yields very small roundoff error.
This makes many of the following divisions look funny.
*/
/* H,L, and S vary over 0-HLSMAX */
/* R,G, and B vary over 0-RGBMAX */
/* HLSMAX BEST IF DIVISIBLE BY 6 */
/* RGBMAX, HLSMAX must each fit in a byte. */
#define UNDEFINED (HLSMAX*2/3)/* Hue is undefined if Saturation is 0 (grey-scale) */
/* This value determines where the Hue scrollbar is */
/* initially set for achromatic colors */
static void RGBtoHLS(DWORD lRGBColor)
{
int R,G,B; /* input RGB values */
WORD cMax,cMin; /* max and min RGB values */
WORD cSum,cDif;
int Rdelta,Gdelta,Bdelta; /* intermediate value: % of spread from max */
/* get R, G, and B out of DWORD */
R = GetRValue(lRGBColor);
G = GetGValue(lRGBColor);
B = GetBValue(lRGBColor);
/* calculate lightness */
cMax = (WORD)max( max(R,G), B);
cMin = (WORD)min( min(R,G), B);
cSum = cMax + cMin;
L = (WORD)(((cSum * (DWORD)HLSMAX) + RGBMAX )/(2*RGBMAX));
cDif = cMax - cMin;
if (!cDif) /* r=g=b --> achromatic case */
{
S = 0; /* saturation */
H = UNDEFINED; /* hue */
}
else /* chromatic case */
{
/* saturation */
if (L <= (HLSMAX/2))
S = (WORD) (((cDif * (DWORD) HLSMAX) + (cSum / 2) ) / cSum);
else
S = (WORD) ((DWORD) ((cDif * (DWORD) HLSMAX) + (DWORD)((2*RGBMAX-cSum)/2) )
/ (2*RGBMAX-cSum));
/* hue */
Rdelta = (int) (( ((cMax-R)*(DWORD)(HLSMAX/6)) + (cDif / 2) ) / cDif);
Gdelta = (int) (( ((cMax-G)*(DWORD)(HLSMAX/6)) + (cDif / 2) ) / cDif);
Bdelta = (int) (( ((cMax-B)*(DWORD)(HLSMAX/6)) + (cDif / 2) ) / cDif);
if ((WORD) R == cMax)
H = Bdelta - Gdelta;
else if ((WORD) G == cMax)
H = (HLSMAX/3) + Rdelta - Bdelta;
else /* B == cMax */
H = ((2*HLSMAX)/3) + Gdelta - Rdelta;
if (H < 0)
H += HLSMAX;
if (H > HLSMAX)
H -= HLSMAX;
}
}
/* utility routine for HLStoRGB */
static WORD NEAR PASCAL HueToRGB(WORD n1, WORD n2, WORD hue)
{
/* range check: note values passed add/subtract thirds of range */
/* The following is redundant for WORD (unsigned int) */
if (hue > HLSMAX)
hue -= HLSMAX;
/* return r,g, or b value from this tridrant */
if (hue < (HLSMAX/6))
return ( n1 + (((n2-n1)*hue+(HLSMAX/12))/(HLSMAX/6)) );
if (hue < (HLSMAX/2))
return ( n2 );
if (hue < ((HLSMAX*2)/3))
return ( n1 + (((n2-n1)*(((HLSMAX*2)/3)-hue)+(HLSMAX/12)) / (HLSMAX/6)) );
else
return ( n1 );
}
static DWORD NEAR PASCAL HLStoRGB(WORD hue, WORD lum, WORD sat)
{
WORD R,G,B; /* RGB component values */
WORD Magic1,Magic2; /* calculated magic numbers (really!) */
if (sat == 0) /* achromatic case */
{
R = G = B = (lum * RGBMAX) / HLSMAX;
if (hue != UNDEFINED)
{
/* ERROR */
}
}
else /* chromatic case */
{
/* set up magic numbers */
if (lum <= (HLSMAX/2))
Magic2 = (WORD)((lum * ((DWORD)HLSMAX + sat) + (HLSMAX/2))/HLSMAX);
else
Magic2 = lum + sat - (WORD)(((lum*sat) + (DWORD)(HLSMAX/2))/HLSMAX);
Magic1 = 2*lum-Magic2;
/* get RGB, change units from HLSMAX to RGBMAX */
R = (WORD)((HueToRGB(Magic1,Magic2,(WORD)(hue+(WORD)(HLSMAX/3)))*(DWORD)RGBMAX + (HLSMAX/2))) / (WORD)HLSMAX;
G = (WORD)((HueToRGB(Magic1,Magic2,hue)*(DWORD)RGBMAX + (HLSMAX/2))) / HLSMAX;
B = (WORD)((HueToRGB(Magic1,Magic2,(WORD)(hue-(WORD)(HLSMAX/3)))*(DWORD)RGBMAX + (HLSMAX/2))) / (WORD)HLSMAX;
}
return(RGB(R,G,B));
}
DWORD FAR PASCAL AdjustLuma(DWORD rgb, int n, BOOL fScale)
{
if (n == 0)
return rgb;
RGBtoHLS(rgb);
if (fScale)
{
if (n > 0)
{
return HLStoRGB((WORD)H, (WORD)(((long)L * (1000 - n) + (RANGE + 1l) * n) / 1000), (WORD)S);
}
else
{
return HLStoRGB((WORD)H, (WORD)(((long)L * (n + 1000)) / 1000), (WORD)S);
}
}
L += (int)((long)n * RANGE / 1000);
if (L < 0)
L = 0;
if (L > HLSMAX)
L = HLSMAX;
return HLStoRGB((WORD)H, (WORD)L, (WORD)S);
}