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st-minimumcontrast-20241029-0.9.2.diff (5744B)

---

 From b0601465dc4d654485db7c3bcb28e019b21e78ca Mon Sep 17 00:00:00 2001
 From: Nick Lott <nick.lott@gmail.com>
 Date: Sun, 13 Oct 2024 11:14:38 +1300
 Subject: [PATCH] Add minimum contrast ratio feature
 
 ---
  Makefile     |   2 +-
  config.def.h |   6 +++
  contrast.c   | 146 +++++++++++++++++++++++++++++++++++++++++++++++++++
  contrast.h   |  11 ++++
  x.c          |  12 +++++
  5 files changed, 176 insertions(+), 1 deletion(-)
  create mode 100644 contrast.c
  create mode 100644 contrast.h
 
 diff --git a/Makefile b/Makefile
 index 15db421..893c71b 100644
 --- a/Makefile
 +++ b/Makefile
 @@ -4,7 +4,7 @@
  
  include config.mk
  
 -SRC = st.c x.c
 +SRC = st.c x.c contrast.c
  OBJ = $(SRC:.c=.o)
  
  all: st
 diff --git a/config.def.h b/config.def.h
 index 2cd740a..03eed3a 100644
 --- a/config.def.h
 +++ b/config.def.h
 @@ -134,6 +134,12 @@ unsigned int defaultbg = 259;
  unsigned int defaultcs = 256;
  static unsigned int defaultrcs = 257;
  
 +
 +/*
 +* Minimum contrast ratio (1-21)
 +*/
 +const float min_contrast_ratio = 2.2f;
 +
  /*
   * Default shape of cursor
   * 2: Block ("█")
 diff --git a/contrast.c b/contrast.c
 new file mode 100644
 index 0000000..d956bd6
 --- /dev/null
 +++ b/contrast.c
 @@ -0,0 +1,146 @@
 +#include <math.h>
 +
 +#include "contrast.h"
 +
 +
 +/* Linear RGB floating point color space for use in calculations  */
 +typedef struct {
 +	float r;
 +	float g;
 +	float b;
 +	float l;
 +} RGBf;
 +
 +
 +
 +static float
 +sRGB_to_lin(const unsigned short c)
 +{
 +	/* Convert to normalized float. */
 +	const float f = c / 65535.0f;
 +
 +	/* Convert from sRGB to linear space. */
 +	return (f <= 0.03928f) ? f / 12.92f : pow((f + 0.055f) / 1.055f, 2.4f);
 +}
 +
 +
 +
 +static unsigned short
 +lin_to_sRGB(const float c)
 +{
 +	/* Convert to sRGB space. */
 +	const float f = (c <= 0.0031308f) ?
 +	                      12.92f * c : 1.055f * pow(c, 1.0f / 2.4f) - 0.055f;
 +
 +	/* Clamp and convert back to 16-bit values. */
 +	return	(unsigned short)(fminf(fmaxf(f * 65535.0f, 0.0f), 65535.0f));
 +}
 +
 +
 +
 +static RGBf
 +XftColor_to_RGBf( XftColor const * const c )
 +{
 +	const float r = sRGB_to_lin(c->color.red);
 +	const float g = sRGB_to_lin(c->color.green);
 +	const float b = sRGB_to_lin(c->color.blue);
 +
 +	/* Calculate luminance. */
 +	const float l = 0.2126f * r + 0.7152f * g + 0.0722f * b;
 +
 +	return (RGBf) {r, g, b, l};
 +}
 +
 +
 +
 +static void
 +RGBf_to_XftColor( const RGBf rgb, XftColor * const c)
 +{
 +	c->color.red   = lin_to_sRGB(rgb.r);
 +	c->color.green = lin_to_sRGB(rgb.g);
 +	c->color.blue  = lin_to_sRGB(rgb.b);
 +}
 +
 +
 +
 +static float
 +get_luminance(XftColor const * const c)
 +{
 +	const RGBf rgb = XftColor_to_RGBf(c);
 +	return rgb.l;
 +}
 +
 +
 +
 +static float
 +get_contrast_ratio(const float fg_lum, const float bg_lum)
 +{
 +	if (fg_lum > bg_lum) {
 +		return (fg_lum + 0.05f) / (bg_lum + 0.05f);
 +	} else {
 +		return (bg_lum + 0.05f) / (fg_lum + 0.05f);
 +	}
 +}
 +
 +
 +
 +static void
 +adjust_luminance(XftColor * const c, const float adjustment)
 +{
 +	/* Convert sRGB to linear space and calculate luminance. */
 +	RGBf rgb = XftColor_to_RGBf(c);
 +
 +	/* Adjust luminance, clamping to 0-100% */
 +	const float factor = fminf(fmaxf(rgb.l + adjustment, 0.0f), 1.0f) / rgb.l;
 +	rgb.r *= factor;
 +	rgb.g *= factor;
 +	rgb.b *= factor;
 +
 +	/* Convert back to sRGB space. */
 +	RGBf_to_XftColor(rgb, c);
 +}
 +
 +
 +static float
 +get_luminance_adjustment( float fl, float bl, float contrast )
 +{
 +	/* Increase existing any luminance difference to get contrast. */
 +	float adjustment = (bl > fl)?
 +	          ((((bl + 0.05f) / min_contrast_ratio) - 0.05f) - fl) :
 +	          (((min_contrast_ratio * (bl + 0.05f)) - 0.05f) - fl);
 +
 +	const float new_lum = fl + adjustment;
 +
 +	/* Use the opposite direction if we exceed valid luminance range. */
 +	if (new_lum < 0.0 || new_lum > 1.0) {
 +		adjustment = (bl <= fl)?
 +		    ((((bl + 0.05f) / min_contrast_ratio) - 0.05f) - fl) :
 +		    (((min_contrast_ratio * (bl + 0.05f)) - 0.05f) - fl);
 +	}
 +
 +	return adjustment;
 +}
 +
 +
 +void
 +adjust_color_for_contrast(XftColor * const fg, XftColor * const bg)
 +{
 +	float fl = get_luminance(fg);
 +	const float bl = get_luminance(bg);
 +	const float contrast = get_contrast_ratio(fl, bl);
 +
 +	if (contrast < min_contrast_ratio) {
 +		/* Change black to dark grey so the luminance calculations can work. */
 +		if (fl < 0.00001) {
 +			fg->color.red   = 0x1fff;
 +			fg->color.green = 0x1fff;
 +			fg->color.blue  = 0x1fff;
 +			fl = get_luminance(fg);
 +		}
 +
 +		const float adjustment = get_luminance_adjustment(
 +		                             fl, bl, min_contrast_ratio);
 +
 +		adjust_luminance(fg, adjustment);
 +	}
 +}
 diff --git a/contrast.h b/contrast.h
 new file mode 100644
 index 0000000..2aa6dd3
 --- /dev/null
 +++ b/contrast.h
 @@ -0,0 +1,11 @@
 +#ifndef __ST_CONTRAST_H_
 +#define __ST_CONTRAST_H_
 +
 +#include <X11/Xft/Xft.h>
 +
 +void adjust_color_for_contrast(XftColor * const , XftColor * const );
 +
 +/* config.h globals */
 +extern const float min_contrast_ratio;
 +
 +#endif
 diff --git a/x.c b/x.c
 index bd23686..4c79e52 100644
 --- a/x.c
 +++ b/x.c
 @@ -19,6 +19,7 @@ char *argv0;
  #include "arg.h"
  #include "st.h"
  #include "win.h"
 +#include "contrast.h"
  
  /* types used in config.h */
  typedef struct {
 @@ -1478,6 +1479,17 @@ xdrawglyphfontspecs(const XftGlyphFontSpec *specs, Glyph base, int len, int x, i
  	if (winy + win.ch >= borderpx + win.th)
  		xclear(winx, winy + win.ch, winx + width, win.h);
  
 +
 +	/*
 +	 * Adjust colours to enforce a minimum contrast. Using the local truefg/bg
 +	 * here to ensure we don't alter the dc.cols table permanently.
 +	 */
 +	fg = memcpy( &truefg, fg, sizeof(Color));
 +	bg = memcpy( &truebg, bg, sizeof(Color));
 +
 +	adjust_color_for_contrast( fg, bg);
 +
 +
  	/* Clean up the region we want to draw to. */
  	XftDrawRect(xw.draw, bg, winx, winy, width, win.ch);
  
 -- 
 2.34.1