Speedup overlong text detection

Detecting very long window titles is done via FbTk::TextUtils::doAlignment().
Instead of removing one char from the title at a time to see if it fits into a
given 'max_width', we now use a binary-search like approach to get faster to
the right value. This massively improves the speed for windows with
(arbitrary) long window titles (see bug #1090, javascript

    document.title = new Array(4999).join(".");

leads to massive waiting for fluxbox to detect that this window has a very
long title).

In addition to that Xft returns 'wrapped' shorts ('integer overflows') for
long texts: XGlpyhInfo.xOff is declared as signed short, it's able to hold
~32k pixels. A monospace font with font-size 10 produces an integer
overflow after 3276 chars / glyphs, thus rendering the check

    if (text_width < max_width) { /* ... */ }

pointless and leading rendering the whole title. By calculating some kind of
upper limit for a pseudo-wide glyph ("WW") and strictly cutting off the input
string at that limit prevents this issue.

1 files changed, 15 insertions, 2 deletions

diff --git a/src/FbTk/XftFontImp.cc b/src/FbTk/XftFontImp.cc
index 15c8212..9e57349 100644
--- a/src/FbTk/XftFontImp.cc
+++ b/src/FbTk/XftFontImp.cc
@@ -23,7 +23,9 @@
 #include "App.hh"
 #include "FbDrawable.hh"
 
-#include <math.h>
+#include <cmath>
+#include <cstdio>
+#include <algorithm>
 
 #ifdef HAVE_CONFIG_H
 #include "config.h"
@@ -32,7 +34,7 @@
 namespace FbTk {
 
 XftFontImp::XftFontImp(const char *name, bool utf8):
-    m_utf8mode(utf8), m_name("") {
+    m_utf8mode(utf8), m_name(""), m_maxlength(0x8000) {
 
     for (int r = ROT0; r <= ROT270; r++) {
         m_xftfonts[r] = 0;
@@ -74,6 +76,15 @@ bool XftFontImp::load(const std::string &name) {
     m_xftfonts_loaded[ROT0] = true;
     m_name = name;
 
+    // XGlyphInfo (used by XftFontImp::textWidth() / XftTextExtents8() etc)
+    // holds only type 'short' or 'unsigned short'. any text bigger than that
+    // yields either some negative or some 'wrapped' values ('integer
+    // overflow'). to prevent something like this we detect the maximium
+    // number of glyphs by calculating the amount of 'WW' (pretending a 'wide'
+    // glyph) fitting into 32k pixels 
+    unsigned int tw = textWidth("WW", 2);
+    m_maxlength = 0x8000 / tw;
+
     return true;
 }
 
@@ -160,6 +171,8 @@ unsigned int XftFontImp::textWidth(const char* text, unsigned int len) const {
 
     XftFont *font = m_xftfonts[ROT0];
 
+    len = std::min(len, m_maxlength);
+
 
 #ifdef HAVE_XFT_UTF8_STRING
     if (m_utf8mode) {