Misc: added misc/text_select/ extension: select and copy any drawn text, using ImDrawListSharedData::TextHook.

docs/CHANGELOG.txt

@@ -100,6 +100,8 @@ Other Changes:
   with the font, position, clip rectangle and string of every text run before its glyphs
   are emitted, and `ImGuiItemFlags_NoTextSelect` to let such a hook skip items. Enables
   text selection/copy of any displayed text without changes to widget code.
+- Misc: added misc/text_select/ extension using the hook above: mouse selection
+  (click/drag, word, line, block), highlight, and Ctrl+C/Cmd+C copy of any drawn text.
 - ImVec2: added a check for cases where a custom `IM_VEC2_CLASS_EXTRA` macro
   adds an extra `operator=` to ImVec2. This isn't supported but should not
   be needed as you should have a constructor to convert from your type to ImVec2.

misc/README.txt

@@ -16,6 +16,10 @@ misc/freetype/
   Font atlas builder/rasterizer using FreeType instead of stb_truetype.
   Benefit from better FreeType rasterization, in particular for small fonts.
 
+misc/text_select/
+  Text selection extension: select and copy any text Dear ImGui draws, by screen position,
+  without changes to widget code. Relies on ImDrawListSharedData::TextHook.
+
 misc/single_file/
   Single-file header stub.
   We use this to validate compiling all *.cpp files in a same compilation unit.

misc/text_select/imgui_text_select.h

@@ -0,0 +1,87 @@
+// dear imgui: text selection extension
+// Select and copy any text Dear ImGui draws, by screen position, without changing how widgets render it.
+// - Click where no widget takes the click to set the anchor (a caret shows at the nearest glyph edge), then
+//   Shift+Click or drag to set the other end. Double-Click selects a word, Double-Click+drag extends by words,
+//   Shift+Double-Click extends the selection to include the whole word. Triple-Click selects the line (all text on
+//   that line of the window), Triple-Click+drag extends by lines, Shift+Triple-Click extends to the whole line.
+// - Shift+Alt+Click, or Shift+Alt held while dragging, selects a block: the glyphs inside the rectangle spanned
+//   by the two ends, copied as one line per row.
+// - Both ends stay inside the container the anchor was set in: its window and, when set in a table, that table. Dragging
+//   past the container's edge scrolls it, faster the longer the mouse stays out, and extends the selection to the
+//   nearest point inside it. A table's frozen rows and columns come before its scrolling ones.
+// - Every glyph of the container drawn between the two ends in reading order is highlighted, with bookend markers on
+//   the first and last selected glyphs. Child windows inside the container take part only when they overlap the
+//   rectangle spanned by the two ends (selecting in one of two side-by-side children leaves the other out).
+// - A word is a run of word characters, or a run of delimiter characters (see TextSelectSetWordDelimiters()).
+// - Ctrl+C (Cmd+C on macOS) or Ctrl+Insert copies the selection in reading order: lines from top to bottom,
+//   fragments on a line from left to right, wide gaps (e.g. table columns) as tabs, soft-wrapped lines joined by a space
+//   (or as given to TextSelectMarkSoftWrap()). The container's rows and columns scrolled out of view are submitted for
+//   that one frame (through ImGuiListClipper and tables' box-select unclip support) and copied; hidden columns are not.
+// - Escape, or a click on a widget other than the container's scrollbars, clears the selection.
+// - When io.ConfigWindowsMoveFromTitleBarOnly is off, a click on background farther than the width of an 'M' (in the
+//   text's font) from any text on its line clears the selection and a drag there moves the window; closer, it selects.
+// - A click on a widget's text stays the widget's click. On a TreeNode or a row-spanning Selectable, dragging it past
+//   the drag threshold turns it into a selection instead, unless the widget already used the drag (edited a value,
+//   started a drag and drop). Any other widget starts a selection only with Alt held.
+// Requires ImDrawListSharedData::TextHook, which ImDrawList::AddText() calls before emitting glyphs.
+// Opt-out: PushItemFlag(ImGuiItemFlags_NoTextSelect, true) for text, TextSelectPushDisabledRegion() for an area.
+
+#pragma once
+
+#include "imgui.h"
+
+#ifndef IMGUI_TEXT_SELECT_FLASH_DURATION
+#define IMGUI_TEXT_SELECT_FLASH_DURATION 0.20f    // Seconds the highlight takes to fade back from opaque after a copy
+#endif
+
+#ifndef IMGUI_TEXT_SELECT_DEFAULT_DELIMITERS
+#define IMGUI_TEXT_SELECT_DEFAULT_DELIMITERS "'\"`|:,()[]{}<>"
+#endif
+
+struct ImGuiTextSelectCopyLine
+{
+    ImVec2      Pos;        // Screen position of the line's first copied glyph
+    bool        Visible;    // The first glyph was inside its clip rectangle (not scrolled out of view)
+    const char* Text;       // Points into the full copied text
+    const char* TextEnd;
+};
+
+// Called after a copy has set the clipboard, instead of the built-in feedback (the highlight flashes opaque and
+// fades back over IMGUI_TEXT_SELECT_FLASH_DURATION). Pointers are valid only during the call.
+typedef void (*ImGuiTextSelectCopyFeedbackCallback)(const char* text, const ImGuiTextSelectCopyLine* lines, int lines_count, void* user_data);
+
+namespace ImGui
+{
+    // Installs into the current context. Safe to call every frame. The state is freed with the context.
+    void        TextSelectInstall();
+    void        TextSelectSetEnabled(bool enabled);
+    void        TextSelectSetCopyFeedbackCallback(ImGuiTextSelectCopyFeedbackCallback callback, void* user_data);
+    // ASCII characters that end a word, besides blanks. Other characters, including all non-ASCII, are word characters.
+    void        TextSelectSetWordDelimiters(const char* delimiters);
+
+    // Text drawn in between is ignored (as ImGuiItemFlags_NoTextSelect), and clicks on that stretch of the current
+    // window, from the cursor at Push to the cursor at Pop, do not set the anchor.
+    void        TextSelectPushDisabledRegion();
+    void        TextSelectPopDisabledRegion();
+
+    // The next text drawn in the current window copies as this text, once, when any of its glyphs is selected.
+    // E.g. the full value of a text drawn truncated. Only needed while TextSelectIsCopying(). NULL clears it, e.g. after
+    // drawing in case nothing reached AddText() (a truncation down to just the ellipsis character).
+    void        TextSelectSetNextCopyText(const char* text, const char* text_end = NULL);
+    // Treats a rectangle as one selectable unit with the given copy text, e.g. for text drawn with
+    // ImGuiItemFlags_NoTextSelect or without AddText() (animated digits). Highlights it when selected.
+    void        TextSelectAddText(const ImVec2& p_min, const ImVec2& p_max, const char* text, const char* text_end = NULL);
+
+    // The next text drawn in the current window continues the previous line (a soft wrap done by the caller):
+    // copies join the two with join (a static string, "" for a word cut in two) instead of a newline.
+    void        TextSelectMarkSoftWrap(const char* join = " ");
+    // Selects everything in the current window and its child windows (e.g. on Ctrl+A in a text view).
+    void        TextSelectSelectAll();
+    // Selects the text inside a rectangle of the current window and copies it on the next frame, with the usual copy
+    // feedback, e.g. from a click handler. copy_text, when given, is what reaches the clipboard instead.
+    void        TextSelectSelectAndCopy(const ImVec2& p_min, const ImVec2& p_max, const char* copy_text = NULL, const char* copy_text_end = NULL);
+
+    bool        TextSelectHasSelection(bool current_window_only = false);   // current_window_only: in the current window's root
+    bool        TextSelectIsCopying();          // True during the frame whose text is being collected for a copy
+    void        TextSelectClear();
+}