Skip missing font glyphs to 1) avoid using space for missing glyphs and 2) allow merging fonts with overlapping ranges. Demo: Fixed displaying ? instead of greyed out empty box. (#1671, #1703)

CHANGELOG.txt

@@ -64,6 +64,8 @@ Other Changes:
 - DragFloat, SliderFloat: Rounding-on-write uses the provided format string instead of parsing the precision from the string, which allows for finer uses of %e %g etc. (#648, #642)
 - Nav: Fixed hovering a Selectable() with the mouse so that it update the navigation cursor (as it happened in the pre-1.60 navigation branch). (#787)
 - Style: Changed default style.DisplaySafeAreaPadding values from (4,4) to (3,3) so it is smaller than FramePadding and has no effect on main menu bar on a computer. (#1439)
+- Fonts: When building font atlas, glyphs that are missing in the fonts are not using the glyph slot to render a dummy/default glyph. Saves space and allow merging fonts with 
+  overlapping font ranges such as FontAwesome5 which split out the Brands separately from the Solid fonts. (#1703, #1671)
 - Misc: Added IMGUI_CHECKVERSION() macro to compare version string and data structure sizes in order to catch issues with mismatching compilation unit settings. (#1695, #1769)
 - Demo: Fixed Overlay: Added a context menu item to enable freely moving the window. 
 - Examples: Calling IMGUI_CHECKVERSION() in the main.cpp of every example application.

imgui_demo.cpp

@@ -2288,7 +2288,8 @@ void ImGui::ShowStyleEditor(ImGuiStyle* ref)
                                 ImVec2 cell_p2(cell_p1.x + cell_size, cell_p1.y + cell_size);
                                 const ImFontGlyph* glyph = font->FindGlyphNoFallback((ImWchar)(base+n));
                                 draw_list->AddRect(cell_p1, cell_p2, glyph ? IM_COL32(255,255,255,100) : IM_COL32(255,255,255,50));
-                                font->RenderChar(draw_list, cell_size, cell_p1, ImGui::GetColorU32(ImGuiCol_Text), (ImWchar)(base+n)); // We use ImFont::RenderChar as a shortcut because we don't have UTF-8 conversion functions available to generate a string.
+                                if (glyph)
+                                    font->RenderChar(draw_list, cell_size, cell_p1, ImGui::GetColorU32(ImGuiCol_Text), (ImWchar)(base+n)); // We use ImFont::RenderChar as a shortcut because we don't have UTF-8 conversion functions available to generate a string.
                                 if (glyph && ImGui::IsMouseHoveringRect(cell_p1, cell_p2))
                                 {
                                     ImGui::BeginTooltip();

stb_textedit.h

@@ -1,4 +1,4 @@
-// [ImGui] this is a slightly modified version of stb_truetype.h 1.9. Those changes would need to be pushed into nothings/sb
+// [ImGui] this is a slightly modified version of stb_textedit.h 1.9. Those changes would need to be pushed into nothings/stb
 // [ImGui] - fixed linestart handler when over last character of multi-line buffer + simplified existing code (#588, #815)
 // [ImGui] - fixed a state corruption/crash bug in stb_text_redo and stb_textedit_discard_redo (#715)
 // [ImGui] - fixed a crash bug in stb_textedit_discard_redo (#681)

stb_truetype.h

@@ -1,3 +1,6 @@
+// [ImGui] this is a slightly modified version of stb_truetype.h 1.19. Those changes would need to be pushed into nothings/stb
+// [ImGui] - skip missing glyphs instead of allocating and rendering a default glyph (stb #607, imgui #1703, imgui #1671)
+
 // stb_truetype.h - v1.19 - public domain
 // authored from 2009-2016 by Sean Barrett / RAD Game Tools
 //
@@ -3968,13 +3971,17 @@ STBTT_DEF int stbtt_PackFontRangesGatherRects(stbtt_pack_context *spc, const stb
          int x0,y0,x1,y1;
          int codepoint = ranges[i].array_of_unicode_codepoints == NULL ? ranges[i].first_unicode_codepoint_in_range + j : ranges[i].array_of_unicode_codepoints[j];
          int glyph = stbtt_FindGlyphIndex(info, codepoint);
-         stbtt_GetGlyphBitmapBoxSubpixel(info,glyph,
-                                         scale * spc->h_oversample,
-                                         scale * spc->v_oversample,
-                                         0,0,
-                                         &x0,&y0,&x1,&y1);
-         rects[k].w = (stbrp_coord) (x1-x0 + spc->padding + spc->h_oversample-1);
-         rects[k].h = (stbrp_coord) (y1-y0 + spc->padding + spc->v_oversample-1);
+         if (glyph != 0) {
+            stbtt_GetGlyphBitmapBoxSubpixel(info,glyph,
+                                            scale * spc->h_oversample,
+                                            scale * spc->v_oversample,
+                                            0,0,
+                                            &x0,&y0,&x1,&y1);
+            rects[k].w = (stbrp_coord) (x1-x0 + spc->padding + spc->h_oversample-1);
+            rects[k].h = (stbrp_coord) (y1-y0 + spc->padding + spc->v_oversample-1);
+         } else {
+            rects[k].w = rects[k].h = 0;
+         }
          ++k;
       }
    }
@@ -4027,7 +4034,7 @@ STBTT_DEF int stbtt_PackFontRangesRenderIntoRects(stbtt_pack_context *spc, const
       sub_y = stbtt__oversample_shift(spc->v_oversample);
       for (j=0; j < ranges[i].num_chars; ++j) {
          stbrp_rect *r = &rects[k];
-         if (r->was_packed) {
+         if (r->was_packed && r->w != 0 && r->h != 0) {
             stbtt_packedchar *bc = &ranges[i].chardata_for_range[j];
             int advance, lsb, x0,y0,x1,y1;
             int codepoint = ranges[i].array_of_unicode_codepoints == NULL ? ranges[i].first_unicode_codepoint_in_range + j : ranges[i].array_of_unicode_codepoints[j];