From e07b082eb810d2088c92b97d04e864a4ab95816f Mon Sep 17 00:00:00 2001
From: ruevs <dpr@ruevs.com>
Date: Thu, 16 Dec 2021 18:51:27 +0200
Subject: [PATCH] Fix hang when trying to display characters missing from the
 embedded font
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

When SolveSpace tries to display an Unicode code point (e.g. U+EA00 )
that does not exist in the embedded vector font (unifont.hex.gz) it hangs
in an endless loop in
`const BitmapFont::Glyph &BitmapFont::GetGlyph(char32_t codepoint)`.

The reason is that the binary search through the text file unifont-8.0.01.hex
that does the "lazy loading" of glyphs does not end.

Here is a short excerpt from the file:

```
D7FE:00007FFE63866DF66DEE6DDE63DE7FFE7FFE61866FBE638E6FBE6F867FFE0000
D7FF:00007FFE63866DF66DEE6DDE63DE7FFE7FFE61866FBE638E6FBE6FBE7FFE0000
F900:0080108810881FF8100800007FFE00000FF008100FF00810042002447FFE0000
F901:00047FFE008010841FFE10841FFC10841FFC10840880050003000CC0703E0000
```

When searching for `0xEA00` after some iterations of the while loop
https://github.com/solvespace/solvespace/blob/2450010bbfa20a1ffbf5fd90b85c4b941f56cb16/src/resource.cpp#L567
both `first` and `last` end up pointing to F900. After that on each
consecutive iteration of the loop `last` ends up pointing to the LF (0x0A)
just before F900
https://github.com/solvespace/solvespace/blob/2450010bbfa20a1ffbf5fd90b85c4b941f56cb16/src/resource.cpp#L585
and then `mid` ends up back on F900 here
https://github.com/solvespace/solvespace/blob/2450010bbfa20a1ffbf5fd90b85c4b941f56cb16/src/resource.cpp#L570
and this will repeat enlessly.

The solution is to do
```
                    first++;
```
here
https://github.com/solvespace/solvespace/blob/2450010bbfa20a1ffbf5fd90b85c4b941f56cb16/src/resource.cpp#L591,
which will make `first==last` and change whe while loop contition to `while(first < last) {` thiw will
allow the while loop to exit.

Tested with
- 0xEA00 - non existent, not found in 16 iterations.
- 0xF900 - exists but takes exactly 16 iterations of the binary search to finish
- 0x0000 - found in 16 iterations
- 0xFFFD - the replacement Unicode code point for non-existing glyphs. Also the end of the font.
- 0xFFFFF - a codepoint beyond the end, not found and does not cause an exception

The lazy parsing of the vector front was introduced here.
https://github.com/solvespace/solvespace/commit/645c2d90ace3e48c639c49512fe1d7a43beb1755

Fixes #1150
---
 src/resource.cpp | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/resource.cpp b/src/resource.cpp
index 7b19081..258c73a 100644
--- a/src/resource.cpp
+++ b/src/resource.cpp
@@ -564,7 +564,7 @@ const BitmapFont::Glyph &BitmapFont::GetGlyph(char32_t codepoint) {
     // Find the hex representation in the (sorted) Unifont file.
     auto first = unifontData.cbegin(),
          last  = unifontData.cend();
-    while(first <= last) {
+    while(first < last) {
         auto mid = first + (last - first) / 2;
         while(mid != unifontData.cbegin()) {
             if(*mid == '\n') {
@@ -588,7 +588,10 @@ const BitmapFont::Glyph &BitmapFont::GetGlyph(char32_t codepoint) {
         if(foundCodepoint < codepoint) {
             first = mid + 1;
             while(first != unifontData.cend()) {
-                if(*first == '\n') break;
+                if(*first == '\n') {
+                    first++;
+                    break;
+                }
                 first++;
             }
             continue; // and last stays the same