Made PushID() behave the same in 32-bit and 64-bit, by not padding the integer into a void*. (Also technically faster.)

Synced/merged minor cruft from docking branch to minimize drift. AFAIK the only meaningful no-op change is that the call UpdateHoveredWindowAndCaptureFlags() was moved above UpdateMouseMovingNewFrame() to match what docking branch has been doing for a while.

Revert "Changed syntax for (very rarely used) IMGUI_OVERRIDE_DRAWVERT_STRUCT_LAYOUT mechanism, instead you only need to '#define ImDrawVert MyDrawVert' to use this feature, avoiding the need to declare the entire structure within an awkward macro. Using the old macro will now error with a message pointing you to the new method. (#38, #103, #1172, #1231, #2489)" ...

This reverts commit 597c024.

Changed syntax for (very rarely used) IMGUI_OVERRIDE_DRAWVERT_STRUCT_LAYOUT mechanism, instead you only need to '#define ImDrawVert MyDrawVert' to use this feature, avoiding the need to declare the entire structure within an awkward macro. Using the old macro will now error with a message pointing you to the new method. (#38, #103, #1172, #1231, #2489)

Window: Fixed one case where auto-resize by double-clicking the resize grip would make either scrollbar appear for a single frame after the resize. Moved Scrollbar visibility block.

Internals: Moved scrollbar visibility calculation block below the call to UpdateManualResize(). This commit is _intended_ to have no side-effect (next commit will). Also moved ItemWidthDefault calculation below rectangles.

Scrollbar overlap an extra WindowBorderSize amount on the left to make all distances consistent. Reverted to BorderSize not affecting work/contents rectangles. Scrollbar, Style: Changed default style.ScrollbarSize from 16 to 14.

Internals: Minor no-op tidying up toward solving the WindowPadding / WindowBorderSize / ScrollbarSize overlapping mess. ...

+ Demo: Use SetScrollY().

Fixed newly created window (e.g. appearing child window) from having scrollbar active on the first frame. (fix 6e03b27) + reworded code a little. (+1 squashed commits) ...

Fixed auto-resize with AlwaysVerticalScrollbar or AlwaysHorizontalScrollbar flags not taking account of the expect scrollbar sizes.

Internals: Storing ScrollMax into a member. Mostly to facilitate debugging. Also locking down window->Scroll slightly lower in the Begin function.

TextWrapped, PushTextWrapPos(0.0f) within a window with horizontal scrolling from not covering the full horizontal area (previously only worked with an explicit contents size).

Internals: Renamed SizeContents to ContentSize, SizeContentsExplicit to ContentSizeExplicit. Tweaked Metrics->Show Rectangles functionality.

Window rectangles: Changed WorkRect to cover the whole region including scrolling (toward obsolete ContentsRegionRect) + using full WindowPadding*1 padding. ...

Tweaked InnerClipRect.
TreeNode, CollapsingHeader: Fixed highlight frame not covering horizontal area fully when using horizontal scrolling. (#2211, #2579)
TabBar: Fixed BeginTabBar() within a window with horizontal scrolling from creating a feedback loop with the horizontal contents size.
Columns: Fixed Columns() within a window with horizontal scrolling from not covering the full horizontal area (previously only worked with an explicit contents size). (#125)
Demo: Added demo code to test contentsrect/workrect

Clarified behavior of SetNextWindowContentSize(). Content size is defined as the size available after removal of WindowPadding on each sides. So SetNextWindowContentSize(ImVec2(100,100)) + auto-resize will always allow submitting a 100x100 item without creating a scrollbar, regarding of WindowPadding.The exact meaning of ContentSize for decorated windows was previously ill-defined.

Window rectangles: Made InnerRect not affected by window border sizes. its few users shouldn't be meaningfully affected.

Nav: Fixed rare crash when e.g. releasing Alt-key while focusing a window with a menu at the same frame as clearing the focus. This was in most noticeable in some back-ends with emits key release events when focusing another viewport. (#2609)

Nav: Fixed gamepad/keyboard moving of window affecting contents size incorrectly, sometimes leading to scrollbars appearing during the movement. + minor fix with the mostly dead Ctrl+wheel scaling.

Internals: Window rectangles: Fixed ContentsRegion lag by moving back after Scrollbar, fixes b50c61c9. Shuffling setup order and added comments.

Internals: Window rectangles: Renaming of all rectangles toward their final form. Should be a no-op. Renamed GetWorkRectMax() to GetContentRegionMaxAbs(). Metrics shows SizeContents.

Renamed ImGuiBackendFlags_HasVtxOffset to ImGuiBackendFlags_RendererHasVtxOffset to match naming convention already used in viewport/docking branch. (#2591) + Fix OpenGL3 code missing flag.

ImDrawList: Added ImDrawCmd::VtxOffset value to support large meshes (64k+ vertices) using 16-bits indices. To enable the feature, the renderer back-end needs to set 'io.BackendFlags |= ImGuiBackendFlags_HasVtxOffset' and honor the ImDrawCmd::VtxOffset field. Otherwise the value will always be zero. This has the advantage of preserving smaller index buffers and allowing to execute on hardware that do not support 32-bits indices. ...

ImDrawList: Added ImDrawCmd::IdxOffset value, equivalent to summing element count for each draw command. This is provided for convenience and consistency with VtxOffset. (#2591)

ImDrawList: Store initial flags for the frame in ImDrawListSharedData, reducing code duplication in setting up the flags.

Internal: Renamed InnerMainRect to InnerVisibleRect. Printing coordinates in Metrics window.

Added full "Dear ImGui" prefix to the title of "Dear ImGui Demo" and "Dear ImGui Metrics" windows. Shortened amount of nodes in columns>tree demo.

Style: Added style.WindowMenuButtonPosition (left/right, defaults to ImGuiDir_Left) to move the collapsing/docking button to the other side of the title bar.

Internal: CloseButton takes an upper-left corner + a size to be consistent with similar widgets.

Internals: Added InnerWorkRect equal to old InnerClipRect, added InnerWorkRectClipped actually clipped.

Fix OuterRectClipped not being clipped correctly, which resulted in child window outside visible bound to not be marked with SkipItems. Broken in b50c61c. ...

+ Comments on InnerClipRect being misleading. Demo: Tweak to sizing of child window in the Layout->Scrolling section.

Fixed crash when appending with BeginMainMenuBar() more than once and no other window are showing. (#2567) + comments

BeginPopupContextItem(): Skip processing when SkipItems is set as LastItemId is unreliable and we assert when it is zero. + Minor comments on columns.