InputText: Added support for Page Up/Down in InputTextMultiline. (#3430)

+ fix stb_textedit.h to build with C language (amend fbf70070)

docs/CHANGELOG.txt

@@ -50,6 +50,7 @@ Other Changes:
 - Nav: Fixed using Alt to toggle the Menu layer when inside a Modal window. (#787)
 - Scrolling: Fixed SetScrollHere functions edge snapping when called during a frame where ContentSize
   is changing (issue introduced in 1.78). (#3452).
+- InputText: Added support for Page Up/Down in InputTextMultiline(). (#3430) [@Xipiryon]
 - InputText: Added selection helpers in ImGuiInputTextCallbackData().
 - InputText: Added ImGuiInputTextFlags_CallbackEdit to modify internally owned buffer after an edit.
   (note that InputText() already returns true on edit, the callback is useful mainly to manipulate the
@@ -59,8 +60,9 @@ Other Changes:
 - InputText: Fixed minor scrolling glitch when erasing trailing lines in InputTextMultiline().
 - InputText: Fixed cursor being partially covered after using Ctrl+End key.
 - InputText: Fixed callback's helper DeleteChars() function when cursor is inside the deleted block. (#3454)
-- InputText: Fixed minor inconsistency when pressing Down on the last line when it doesn't have a carriage 
+- InputText: Made pressing Down arrow on the last line when it doesn't have a carriage return not move to the end
-  return (it used to move to the end of the line). [@Xipiryon]
+  of the line (so it is consistent with Up arrow, and behave same as Notepad and Visual Studio. Note that some 
+  other text editors instead would move the crusor to the end of the line). [@Xipiryon]
 - DragFloat, DragScalar: Fixed ImGuiSliderFlags_ClampOnInput not being honored in the special case
   where v_min == v_max. (#3361)
 - SliderInt, SliderScalar: Fixed reaching of maximum value with inverted integer min/max ranges, both

imgui_widgets.cpp

@@ -3590,6 +3590,8 @@ static bool STB_TEXTEDIT_INSERTCHARS(STB_TEXTEDIT_STRING* obj, int pos, const Im
 #define STB_TEXTEDIT_K_REDO         0x20000B // keyboard input to perform redo
 #define STB_TEXTEDIT_K_WORDLEFT     0x20000C // keyboard input to move cursor left one word
 #define STB_TEXTEDIT_K_WORDRIGHT    0x20000D // keyboard input to move cursor right one word
+#define STB_TEXTEDIT_K_PGUP         0x20000E // keyboard input to move cursor up a page
+#define STB_TEXTEDIT_K_PGDOWN       0x20000F // keyboard input to move cursor down a page
 #define STB_TEXTEDIT_K_SHIFT        0x400000
 
 #define STB_TEXTEDIT_IMPLEMENTATION
@@ -3856,6 +3858,8 @@ bool ImGui::InputTextEx(const char* label, const char* hint, char* buf, int buf_
     bool clear_active_id = false;
     bool select_all = (g.ActiveId != id) && ((flags & ImGuiInputTextFlags_AutoSelectAll) != 0 || user_nav_input_start) && (!is_multiline);
 
+    float scroll_y = is_multiline ? draw_window->Scroll.y : FLT_MAX;
+
     const bool init_make_active = (focus_requested || user_clicked || user_scroll_finish || user_nav_input_start);
     const bool init_state = (init_make_active || user_scroll_active);
     if (init_state && g.ActiveId != id)
@@ -3916,7 +3920,7 @@ bool ImGui::InputTextEx(const char* label, const char* hint, char* buf, int buf_
         g.ActiveIdUsingNavInputMask |= (1 << ImGuiNavInput_Cancel);
         g.ActiveIdUsingKeyInputMask |= ((ImU64)1 << ImGuiKey_Home) | ((ImU64)1 << ImGuiKey_End);
         if (is_multiline)
-            g.ActiveIdUsingKeyInputMask |= ((ImU64)1 << ImGuiKey_PageUp) | ((ImU64)1 << ImGuiKey_PageDown); // FIXME-NAV: Page up/down actually not supported yet by widget, but claim them ahead.
+            g.ActiveIdUsingKeyInputMask |= ((ImU64)1 << ImGuiKey_PageUp) | ((ImU64)1 << ImGuiKey_PageDown);
         if (flags & (ImGuiInputTextFlags_CallbackCompletion | ImGuiInputTextFlags_AllowTabInput))  // Disable keyboard tabbing out as we will use the \t character.
             g.ActiveIdUsingKeyInputMask |= ((ImU64)1 << ImGuiKey_Tab);
     }
@@ -4055,6 +4059,9 @@ bool ImGui::InputTextEx(const char* label, const char* hint, char* buf, int buf_
         IM_ASSERT(state != NULL);
         IM_ASSERT(io.KeyMods == GetMergedKeyModFlags() && "Mismatching io.KeyCtrl/io.KeyShift/io.KeyAlt/io.KeySuper vs io.KeyMods"); // We rarely do this check, but if anything let's do it here.
 
+        const int row_count_per_page = ImMax((int)((inner_size.y - style.FramePadding.y) / g.FontSize), 1);
+        state->Stb.row_count_per_page = row_count_per_page;
+
         const int k_mask = (io.KeyShift ? STB_TEXTEDIT_K_SHIFT : 0);
         const bool is_osx = io.ConfigMacOSXBehaviors;
         const bool is_osx_shift_shortcut = is_osx && (io.KeyMods == (ImGuiKeyModFlags_Super | ImGuiKeyModFlags_Shift));
@@ -4074,6 +4081,8 @@ bool ImGui::InputTextEx(const char* label, const char* hint, char* buf, int buf_
         else if (IsKeyPressedMap(ImGuiKey_RightArrow))                  { state->OnKeyPressed((is_startend_key_down ? STB_TEXTEDIT_K_LINEEND : is_wordmove_key_down ? STB_TEXTEDIT_K_WORDRIGHT : STB_TEXTEDIT_K_RIGHT) | k_mask); }
         else if (IsKeyPressedMap(ImGuiKey_UpArrow) && is_multiline)     { if (io.KeyCtrl) SetScrollY(draw_window, ImMax(draw_window->Scroll.y - g.FontSize, 0.0f)); else state->OnKeyPressed((is_startend_key_down ? STB_TEXTEDIT_K_TEXTSTART : STB_TEXTEDIT_K_UP) | k_mask); }
         else if (IsKeyPressedMap(ImGuiKey_DownArrow) && is_multiline)   { if (io.KeyCtrl) SetScrollY(draw_window, ImMin(draw_window->Scroll.y + g.FontSize, GetScrollMaxY())); else state->OnKeyPressed((is_startend_key_down ? STB_TEXTEDIT_K_TEXTEND : STB_TEXTEDIT_K_DOWN) | k_mask); }
+        else if (IsKeyPressedMap(ImGuiKey_PageUp) && is_multiline)      { state->OnKeyPressed(STB_TEXTEDIT_K_PGUP | k_mask); scroll_y -= row_count_per_page * g.FontSize; }
+        else if (IsKeyPressedMap(ImGuiKey_PageDown) && is_multiline)    { state->OnKeyPressed(STB_TEXTEDIT_K_PGDOWN | k_mask); scroll_y += row_count_per_page * g.FontSize; }
         else if (IsKeyPressedMap(ImGuiKey_Home))                        { state->OnKeyPressed(io.KeyCtrl ? STB_TEXTEDIT_K_TEXTSTART | k_mask : STB_TEXTEDIT_K_LINESTART | k_mask); }
         else if (IsKeyPressedMap(ImGuiKey_End))                         { state->OnKeyPressed(io.KeyCtrl ? STB_TEXTEDIT_K_TEXTEND | k_mask : STB_TEXTEDIT_K_LINEEND | k_mask); }
         else if (IsKeyPressedMap(ImGuiKey_Delete) && !is_readonly)      { state->OnKeyPressed(STB_TEXTEDIT_K_DELETE | k_mask); }
@@ -4443,12 +4452,11 @@ bool ImGui::InputTextEx(const char* label, const char* hint, char* buf, int buf_
             if (is_multiline)
             {
                 // Test if cursor is vertically visible
-                float scroll_y = draw_window->Scroll.y;
-                const float scroll_max_y = ImMax((text_size.y + style.FramePadding.y * 2.0f) - inner_size.y, 0.0f);
                 if (cursor_offset.y - g.FontSize < scroll_y)
                     scroll_y = ImMax(0.0f, cursor_offset.y - g.FontSize);
                 else if (cursor_offset.y - inner_size.y >= scroll_y)
                     scroll_y = cursor_offset.y - inner_size.y + style.FramePadding.y * 2.0f;
+                const float scroll_max_y = ImMax((text_size.y + style.FramePadding.y * 2.0f) - inner_size.y, 0.0f);
                 scroll_y = ImClamp(scroll_y, 0.0f, scroll_max_y);
                 draw_pos.y += (draw_window->Scroll.y - scroll_y);   // Manipulate cursor pos immediately avoid a frame of lag
                 draw_window->Scroll.y = scroll_y;

imstb_textedit.h

@@ -148,6 +148,8 @@
 //    STB_TEXTEDIT_K_RIGHT       keyboard input to move cursor right
 //    STB_TEXTEDIT_K_UP          keyboard input to move cursor up
 //    STB_TEXTEDIT_K_DOWN        keyboard input to move cursor down
+//    STB_TEXTEDIT_K_PGUP        keyboard input to move cursor up a page
+//    STB_TEXTEDIT_K_PGDOWN      keyboard input to move cursor down a page
 //    STB_TEXTEDIT_K_LINESTART   keyboard input to move cursor to start of line  // e.g. HOME
 //    STB_TEXTEDIT_K_LINEEND     keyboard input to move cursor to end of line    // e.g. END
 //    STB_TEXTEDIT_K_TEXTSTART   keyboard input to move cursor to start of text  // e.g. ctrl-HOME
@@ -170,10 +172,6 @@
 //    STB_TEXTEDIT_K_TEXTSTART2          secondary keyboard input to move cursor to start of text
 //    STB_TEXTEDIT_K_TEXTEND2            secondary keyboard input to move cursor to end of text
 //
-// Todo:
-//    STB_TEXTEDIT_K_PGUP        keyboard input to move cursor up a page
-//    STB_TEXTEDIT_K_PGDOWN      keyboard input to move cursor down a page
-//
 // Keyboard input must be encoded as a single integer value; e.g. a character code
 // and some bitflags that represent shift states. to simplify the interface, SHIFT must
 // be a bitflag, so we can test the shifted state of cursor movements to allow selection,
@@ -337,6 +335,10 @@ typedef struct
    // each textfield keeps its own insert mode state. to keep an app-wide
    // insert mode, copy this value in/out of the app state
 
+   int row_count_per_page;
+   // page size in number of row.
+   // this value MUST be set to >0 for pageup or pagedown in multilines documents.
+
    /////////////////////
    //
    // private data
@@ -855,12 +857,16 @@ retry:
          break;
 
       case STB_TEXTEDIT_K_DOWN:
-      case STB_TEXTEDIT_K_DOWN | STB_TEXTEDIT_K_SHIFT: {
+      case STB_TEXTEDIT_K_DOWN | STB_TEXTEDIT_K_SHIFT:
+      case STB_TEXTEDIT_K_PGDOWN:
+      case STB_TEXTEDIT_K_PGDOWN | STB_TEXTEDIT_K_SHIFT: {
          StbFindState find;
          StbTexteditRow row;
-         int i, sel = (key & STB_TEXTEDIT_K_SHIFT) != 0;
+         int i, j, sel = (key & STB_TEXTEDIT_K_SHIFT) != 0;
+         int is_page = (key & ~STB_TEXTEDIT_K_SHIFT) == STB_TEXTEDIT_K_PGDOWN;
+         int row_count = is_page ? state->row_count_per_page : 1;
 
-         if (state->single_line) {
+         if (!is_page && state->single_line) {
             // on windows, up&down in single-line behave like left&right
             key = STB_TEXTEDIT_K_RIGHT | (key & STB_TEXTEDIT_K_SHIFT);
             goto retry;
@@ -869,23 +875,25 @@ retry:
          if (sel)
             stb_textedit_prep_selection_at_cursor(state);
          else if (STB_TEXT_HAS_SELECTION(state))
-            stb_textedit_move_to_last(str,state);
+            stb_textedit_move_to_last(str, state);
 
          // compute current position of cursor point
          stb_textedit_clamp(str, state);
          stb_textedit_find_charpos(&find, str, state->cursor, state->single_line);
 
-         // now find character position down a row
+         for (j = 0; j < row_count; ++j) {
-         if (find.length) {
+            float x, goal_x = state->has_preferred_x ? state->preferred_x : find.x;
+            int start = find.first_char + find.length;
+
+            if (find.length == 0)
+               break;
 
             // [DEAR IMGUI]
             // going down while being on the last line shouldn't bring us to that line end
             if (STB_TEXTEDIT_GETCHAR(str, find.first_char + find.length - 1) != STB_TEXTEDIT_NEWLINE)
                break;
 
-            float goal_x = state->has_preferred_x ? state->preferred_x : find.x;
+            // now find character position down a row
-            float x;
-            int start = find.first_char + find.length;
             state->cursor = start;
             STB_TEXTEDIT_LAYOUTROW(&row, str, state->cursor);
             x = row.x0;
@@ -907,17 +915,25 @@ retry:
 
             if (sel)
                state->select_end = state->cursor;
+
+            // go to next line
+            find.first_char = find.first_char + find.length;
+            find.length = row.num_chars;
          }
          break;
       }
          
       case STB_TEXTEDIT_K_UP:
-      case STB_TEXTEDIT_K_UP | STB_TEXTEDIT_K_SHIFT: {
+      case STB_TEXTEDIT_K_UP | STB_TEXTEDIT_K_SHIFT:
+      case STB_TEXTEDIT_K_PGUP:
+      case STB_TEXTEDIT_K_PGUP | STB_TEXTEDIT_K_SHIFT: {
          StbFindState find;
          StbTexteditRow row;
-         int i, sel = (key & STB_TEXTEDIT_K_SHIFT) != 0;
+         int i, j, prev_scan, sel = (key & STB_TEXTEDIT_K_SHIFT) != 0;
+         int is_page = (key & ~STB_TEXTEDIT_K_SHIFT) == STB_TEXTEDIT_K_PGUP;
+         int row_count = is_page ? state->row_count_per_page : 1;
 
-         if (state->single_line) {
+         if (!is_page && state->single_line) {
             // on windows, up&down become left&right
             key = STB_TEXTEDIT_K_LEFT | (key & STB_TEXTEDIT_K_SHIFT);
             goto retry;
@@ -932,11 +948,14 @@ retry:
          stb_textedit_clamp(str, state);
          stb_textedit_find_charpos(&find, str, state->cursor, state->single_line);
 
+         for (j = 0; j < row_count; ++j) {
+            float  x, goal_x = state->has_preferred_x ? state->preferred_x : find.x;
+
             // can only go up if there's a previous row
-         if (find.prev_first != find.first_char) {
+            if (find.prev_first == find.first_char)
+               break;
+
             // now find character position up a row
-            float goal_x = state->has_preferred_x ? state->preferred_x : find.x;
-            float x;
             state->cursor = find.prev_first;
             STB_TEXTEDIT_LAYOUTROW(&row, str, state->cursor);
             x = row.x0;
@@ -958,6 +977,14 @@ retry:
 
             if (sel)
                state->select_end = state->cursor;
+
+            // go to previous line
+            // (we need to scan previous line the hard way. maybe we could expose this as a new API function?)
+            prev_scan = find.prev_first > 0 ? find.prev_first - 1 : 0;
+            while (prev_scan > 0 && STB_TEXTEDIT_GETCHAR(str, prev_scan - 1) != STB_TEXTEDIT_NEWLINE)
+               --prev_scan;
+            find.first_char = find.prev_first;
+            find.prev_first = prev_scan;
          }
          break;
       }
@@ -1081,10 +1108,6 @@ retry:
          state->has_preferred_x = 0;
          break;
       }
-
-// @TODO:
-//    STB_TEXTEDIT_K_PGUP      - move cursor up a page
-//    STB_TEXTEDIT_K_PGDOWN    - move cursor down a page
    }
 }
 
@@ -1356,6 +1379,7 @@ static void stb_textedit_clear_state(STB_TexteditState *state, int is_single_lin
    state->initialized = 1;
    state->single_line = (unsigned char) is_single_line;
    state->insert_mode = 0;
+   state->row_count_per_page = 0;
 }
 
 // API initialize