ImFontGlyphRangesBuilder: Using 32-bits fields for storage instead of 8-bit ones, comments, todo.

docs/TODO.txt

@@ -319,6 +319,7 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - optimization: replace vsnprintf with stb_printf? or enable the defines/infrastructure to allow it (#1038)
  - optimization: add clipping for multi-component widgets (SliderFloatX, ColorEditX, etc.). one problem is that nav branch can't easily clip parent group when there is a move request.
  - optimization: add a flag to disable most of rendering, for the case where the user expect to skip it (#335)
+ - optimization: fully covered window (covered by another with non-translucent bg + WindowRounding worth of padding) may want to clip rendering.
  - optimization: use another hash function than crc32, e.g. FNV1a
  - optimization/render: merge command-lists with same clip-rect into one even if they aren't sequential? (as long as in-between clip rectangle don't overlap)?
  - optimization: turn some the various stack vectors into statically-sized arrays

imgui.h

@@ -13,14 +13,14 @@ Index of this file:
 // Forward declarations and basic types
 // ImGui API (Dear ImGui end-user API)
 // Flags & Enumerations
-// ImVector
+// ImVector<>
 // ImGuiStyle
 // ImGuiIO
 // Misc data structures (ImGuiInputTextCallbackData, ImGuiSizeCallbackData, ImGuiPayload)
 // Obsolete functions
 // Helpers (ImGuiOnceUponAFrame, ImGuiTextFilter, ImGuiTextBuffer, ImGuiStorage, ImGuiListClipper, ImColor)
 // Draw List API (ImDrawCmd, ImDrawIdx, ImDrawVert, ImDrawChannel, ImDrawListFlags, ImDrawList, ImDrawData)
-// Font API (ImFontConfig, ImFontGlyph, ImFontAtlasFlags, ImFontAtlas, ImFont)
+// Font API (ImFontConfig, ImFontGlyph, ImFontGlyphRangesBuilder, ImFontAtlasFlags, ImFontAtlas, ImFont)
 
 */
 
@@ -1155,11 +1155,11 @@ enum ImGuiCond_
 
 //-----------------------------------------------------------------------------
 // Helper: ImVector<>
-// Lightweight std::vector<>-like class to avoid dragging dependencies (also: some implementations of STL with debug enabled are absurdly slow, we bypass it so our code runs fast in debug).
+// Lightweight std::vector<>-like class to avoid dragging dependencies (also, some implementations of STL with debug enabled are absurdly slow, we bypass it so our code runs fast in debug).
 // You generally do NOT need to care or use this ever. But we need to make it available in imgui.h because some of our data structures are relying on it.
 // Important: clear() frees memory, resize(0) keep the allocated buffer. We use resize(0) a lot to intentionally recycle allocated buffers across frames and amortize our costs.
 // Important: our implementation does NOT call C++ constructors/destructors, we treat everything as raw data! This is intentional but be extra mindful of that, 
-// do NOT use this class as a std::vector replacement in your own code!
+// do NOT use this class as a std::vector replacement in your own code! Many of the structures used by dear imgui can be safely initialized by a zero-memset.
 //-----------------------------------------------------------------------------
 
 template<typename T>
@@ -1933,12 +1933,14 @@ struct ImFontGlyph
 };
 
 // Helper to build glyph ranges from text/string data. Feed your application strings/characters to it then call BuildRanges().
+// This is essentially a tightly packed of vector of 64k booleans = 8KB storage.
 struct ImFontGlyphRangesBuilder
 {
-    ImVector<unsigned char> UsedChars;  // Store 1-bit per Unicode code point (0=unused, 1=used)
+    ImVector<int> UsedChars;            // Store 1-bit per Unicode code point (0=unused, 1=used)
-    ImFontGlyphRangesBuilder()          { UsedChars.resize(0x10000 / 8); memset(UsedChars.Data, 0, 0x10000 / 8); }
+
-    bool           GetBit(int n) const  { return (UsedChars[n >> 3] & (1 << (n & 7))) != 0; }
+    ImFontGlyphRangesBuilder()          { UsedChars.resize(0x10000 / 32); memset(UsedChars.Data, 0, 0x10000 / 32); }
-    void           SetBit(int n)        { UsedChars[n >> 3] |= 1 << (n & 7); }  // Set bit 'c' in the array
+    bool           GetBit(int n) const  { int off = (n >> 5); int mask = 1 << (n & 31); return (UsedChars[off] & mask) != 0; } // Get bit n in the array
+    void           SetBit(int n)        { int off = (n >> 5); int mask = 1 << (n & 31); UsedChars[off] |= mask; }              // Set bit n in the array
     void           AddChar(ImWchar c)   { SetBit(c); }                          // Add character
     IMGUI_API void AddText(const char* text, const char* text_end = NULL);      // Add string (each character of the UTF-8 string are added)
     IMGUI_API void AddRanges(const ImWchar* ranges);                            // Add ranges, e.g. builder.AddRanges(ImFontAtlas::GetGlyphRangesDefault()) to force add all of ASCII/Latin+Ext