# st

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    commit 33ad83d49213749f4fcec850327f57a33ca8b921
    parent 40e4d76d227d9c517054036f546acd49431bca42
    Author: Eon S. Jeon <esjeon@lavabit.com>
    Date:   Fri, 19 Jul 2013 01:07:02 -0400

    Improved font caching

    I made a patch that improves the performance of font caching mechanism.
    This is based on a funny behaviour of FontConfig: it was handling
    FcCharSet in a somewhat unexpected way.

    So, we are currently adding "a character" to a new FcCharSet, and then
    add it to a FcPattern. However, if we toss the FcPattern to FontConfig,
    it loads the entire language(charset) that contains the character we
    gave. That is, we don't always have to load a new font for each unknown
    character. Instead, we can reused cached fonts, and this significantly
    reduces the number of calls to extremely slow FontConfig matching
    functions.

    One more thing. I found that, in libXft, there's a function called
    XftCharExists. XftCharIndex internally calls this function, and
    does more stuffs if the character does exist. Since the returned index
    is never used in st, we should call XftCharExists instead of
    XftCharIndex. Please note that I already made this change in the patch.

    Diffstat:
    Mst.c | 63++++++++++++++++++++++-----------------------------------------

    1 file changed, 22 insertions(+), 41 deletions(-)
    diff --git a/st.c b/st.c
    @@ -462,17 +462,12 @@ enum {

     typedef struct {
     	XftFont *font;
    -	long c;
     	int flags;
     } Fontcache;

    -/*
    - * Fontcache is a ring buffer, with frccur as current position and frclen as
    - * the current length of used elements.
    - */
    -
    -static Fontcache frc[1024];
    -static int frccur = -1, frclen = 0;
    +/* Fontcache is an array now. A new font will be appended to the array. */
    +static Fontcache frc[16];
    +static int frclen = 0;

     ssize_t
     xwrite(int fd, char *s, size_t len) {
    @@ -2781,18 +2776,12 @@ xunloadfont(Font *f) {

     void
     xunloadfonts(void) {
    -	int i, ip;
    +	int i;

    -	/*
    -	 * Free the loaded fonts in the font cache. This is done backwards
    -	 * from the frccur.
    -	 */
    -	for(i = 0, ip = frccur; i < frclen; i++, ip--) {
    -		if(ip < 0)
    -			ip = LEN(frc) - 1;
    -		XftFontClose(xw.dpy, frc[ip].font);
    +	/* Free the loaded fonts in the font cache.  */
    +	for(i = 0; i < frclen; i++) {
    +		XftFontClose(xw.dpy, frc[i].font);
     	}
    -	frccur = -1;
     	frclen = 0;

     	xunloadfont(&dc.font);
    @@ -2918,7 +2907,7 @@ void
     xdraws(char *s, Glyph base, int x, int y, int charlen, int bytelen) {
     	int winx = borderpx + x * xw.cw, winy = borderpx + y * xw.ch,
     	    width = charlen * xw.cw, xp, i;
    -	int frp, frcflags;
    +	int frcflags;
     	int u8fl, u8fblen, u8cblen, doesexist;
     	char *u8c, *u8fs;
     	long u8char;
    @@ -3044,7 +3033,7 @@ xdraws(char *s, Glyph base, int x, int y, int charlen, int bytelen) {
     			s += u8cblen;
     			bytelen -= u8cblen;

    -			doesexist = XftCharIndex(xw.dpy, font->match, u8char);
    +			doesexist = XftCharExists(xw.dpy, font->match, u8char);
     			if(!doesexist || bytelen <= 0) {
     				if(bytelen <= 0) {
     					if(doesexist) {
    @@ -3071,14 +3060,10 @@ xdraws(char *s, Glyph base, int x, int y, int charlen, int bytelen) {
     		if(doesexist)
     			break;

    -		frp = frccur;
     		/* Search the font cache. */
    -		for(i = 0; i < frclen; i++, frp--) {
    -			if(frp <= 0)
    -				frp = LEN(frc) - 1;
    -
    -			if(frc[frp].c == u8char
    -					&& frc[frp].flags == frcflags) {
    +		for(i = 0; i < frclen; i++) {
    +			if(XftCharExists(xw.dpy, frc[i].font, u8char)
    +					&& frc[i].flags == frcflags) {
     				break;
     			}
     		}
    @@ -3113,28 +3098,24 @@ xdraws(char *s, Glyph base, int x, int y, int charlen, int bytelen) {
     			/*
     			 * Overwrite or create the new cache entry.
     			 */
    -			frccur++;
    -			frclen++;
    -			if(frccur >= LEN(frc))
    -				frccur = 0;
    -			if(frclen > LEN(frc)) {
    -				frclen = LEN(frc);
    -				XftFontClose(xw.dpy, frc[frccur].font);
    +			if(frclen >= LEN(frc)) {
    +				frclen = LEN(frc) - 1;
    +				XftFontClose(xw.dpy, frc[frclen].font);
     			}

    -			frc[frccur].font = XftFontOpenPattern(xw.dpy,
    +			frc[frclen].font = XftFontOpenPattern(xw.dpy,
     					fontpattern);
    -			frc[frccur].c = u8char;
    -			frc[frccur].flags = frcflags;
    +			frc[frclen].flags = frcflags;
    +
    +			i = frclen;
    +			frclen++;

     			FcPatternDestroy(fcpattern);
     			FcCharSetDestroy(fccharset);
    -
    -			frp = frccur;
     		}

    -		XftDrawStringUtf8(xw.draw, fg, frc[frp].font,
    -				xp, winy + frc[frp].font->ascent,
    +		XftDrawStringUtf8(xw.draw, fg, frc[i].font,
    +				xp, winy + frc[i].font->ascent,
     				(FcChar8 *)u8c, u8cblen);

     		xp += font->width;