ImDrawList: Fix broken channel splitting (broken by d1e8b69) (#2591)

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.

ImFontGlyphRangesBuilder: Fixed unnecessarily over-sized buffer, which incidentally was also not fully cleared. Fixed edge case overflow when adding character 0xFFFF. (#2568)

Fixed GCC mem-access warnings (#2565) ...

+ using "if defined" more consistently for Clang.

Fix undefined behavior (#2561)

Version 1.71 WIP + fixed minor typo

Version 1.70

Amend 48a09a7 with changelog, breaking changes, tweak demo code for spacing. (#2518)

Improved algorithm for mitre joints on thick lines

Misc: Added IM_MALLOC/IM_FREE macros mimicking IM_NEW/IM_DELETE so user doesn't need to revert to using the ImGui::MemAlloc()/MemFree() calls directly.

InputText: Made Shift+Tab consistently do nothing regardless of whether the back-end emits both char and keys or just keys. (#2467, #1336)

Silencing -Wstack-protector (#2459)

Comments, todo list, remove trailing spaces.

Version 1.70 WIP

Version 1.69, comments, typos

Added GetGlyphRangesVietnamese() helper. (#2403)

Fix typos. (#2413)

Fix -Wconversion warning (#2379) ...

The warning was caused by implicit conversion from pointer type which
NULL has to non-pointer type, e.g. if ImTextureID is long int

Internal: InputText: Comments. Renamed internal member. Renamed ImGuiStb->ImStb.

Version 1.69 WIP

Version 1.68

Font: Fixed assert when specifying duplicate/overlapping ranges within a same font. (#2353, #2233)

Examples: Extracted gamepad code into ImGui_ImplGlfw_UpdateGamepads(). Renamed matching Win32 function for consistency. ...

Added more link to nothing's oversample document. Spacing bits.

ImDrawData: Added FramebufferScale field (currently a copy of the value from io.DisplayFramebufferScale). ...

This is to allow render functions being written without pulling any data from ImGuiIO, allowing incoming multi-viewport feature to behave on Retina display and with multiple displays. If you are not using a custom binding, please update your render function code ahead of time, and use draw_data->FramebufferScale instead of io.DisplayFramebufferScale. (#2306, #1676)
Examples: Metal, OpenGL2, OpenGL3: Fixed offsetting of clipping rectangle with ImDrawData::DisplayPos != (0,0) when the display frame-buffer scale scale is not (1,1). While this doesn't make a difference when using master branch, this is effectively fixing support for multi-viewport with Mac Retina Displays on those examples. (#2306) Also using ImDrawData::FramebufferScale instead of io.DisplayFramebufferScale.
Examples: Clarified the use the ImDrawData::DisplayPos to offset clipping rectangles.

ImFont: Rearranged members toward an optimal CalcTextSize() loop. Removed comments from destructor. Made constructor more explicit.

Tabs: Non-docking tab bars are storing names to allow tab list button + whole style scaling. Added ImGuiTabBarFlags_TabListPopupButton flag to show a popup button on manual tab bars. Locking FramePadding for the scope of a tab-bar to avoid sheering/clipping of tab item. Made scaling of tab ellipsis less awkward. (#261, #351)

Fonts: Fixed crash if FontGlobalScale is zero. Correctly debug naming default font if not 13 px. Demo: Moved PopupRounding along with other rounding values. Metrics: Displaying indexes with idx to be correct / less misleading.

Persistently fixing some PVS-Studio static analyzer false positive warnings.

Fix various XCode and PVS-Studio static analyzer warnings (#2309)