ItemAdd(): re-ordering the tests, submission should now be faster.

ItemAdd(), not performing computation for IsItemRectHovered() which does them itself, allowing us in the next commit to optimize ItemAdd() and make its logic more consistent with IsHovered().

Moved implementation of Hovered-related functions next to each others + comments, before I attempt to work on them. No functional change here.

Examples: Avoid using ImColor() to not tempt newcomers into looking at it

Fixed not being able to move a window by clicking on one of its child window (#1337, #635), broken by https://github.com/ocornut/imgui/commit/313d388bba42e0634a02b976dcdbae238d25eddc

Removed extraneous ImGui:: prefixes. Declared ColorEditOptionsPopup in imgui_internals.h. Tweaked internal signatures.

ImFontAtlas: Fixed calling Clear() and rebuilding (broken in 3fe2ecf) thanks @pdoane @mikesart

Combo: Cleaned up, removed unnecessary code (looks like this part went untouched for a long time!).

ImFontAtlas: Added support for CustomRect API to submit custom rectangles to be packed into the atlas / and map them as font glyphs

Minor comments

ImFont: Renamed (supposedly internal) fields (e.g. XAdvance to AdvanceX). Custom text renderers might be affected if they didn't use the GetCharAdvance() helper function.

ImFont: Renamed ImFont::Glyph to ImFontGlyph (for consistency and so ImFontAtlas types can use it without ordering half of the file). Left a redirection type.

ImFontAtlas: Refactored internals API to 1) avoid building lookup table multiple times for merged fonts + 2) allow the mapping of custom icons inside fonts (wip, uncommited)

ImFontAtlas: Comments and minor reorganization of declaration in header file.

ImFont: Split some building code into a AddGlyph() helper (that custom rect code and imgui_freetype can use)

Separator(): output vertical separator when used in horizontal layout mode, so it works in menu bars.

Horizontal layout does the minimum job to be usable internally - not exposed (#97)

Comments, debug code (commented), todo list

Fix static misusage error with decent compilers. Error introduced in 4b82759

WantCaptureMouse: Tweaked logic so WantCaptureMouse can stay false when e.g. hovering over void while an InputText() is active. (#621)

Exposed PushMultiItemsWidths() to imgui_internal.h

Merge pull request #1113 from Urmeli0815/ImGuiSelectableFlags_MenuItem ...

MenuItem: only activate on Release, not on Click (nb: and not on ClickRelease to allow opening menu and selecting something with a single click. Windows seems to behave the same, allowing to click and hold to e.g. Open then move cursor, release on Save and save gets activated)

Begin: Fixed auto-fit calculation code that predict the presence of ascrollbar so it works in the case size constraints are used. I actually don't need this fix now, but earlier experiment with BeginCombo() required this fix.

Begin: Moving some code into a CalcSizeAutoFit() function.

BeginCombo(): rework internals a little to make it easier to provide custom combo-like elements relying in BeginCombo(). ...

BeginPopupEx() doesn't enforce AlwaysAutoResize flag anymore.

Demo: Fixed overlay demo keeps resizing (in case, e.g.: font changes)

SetNextWindowPos: added a ImVec2 pivot parameter for positioning a given a center, bottom-right position, etc. As a generalization of SetNextWindowPosCenter() which is now obsolete. This will be useful for combo-like popups as well. ...

Demo: Simple-overlay window uses the SetWindowPos pivot to select a corner to position itself at.

Begin(): Minor tidying up of flow

Window: Tweaked ApplySizeFullWithConstraint() -> CalcSizeFullWithConstraint() so it can be used without side-effect

Popups: Exposing a little more of popups internals in imgui_internals.h