RenderText(), InputTextMultiline(): Optimization for large text by using memchr, wmemchr, wcschr when appropriate.

docs/CHANGELOG.txt

@@ -59,6 +59,7 @@ Other Changes:
   introduced in 1.50 and broken in 1.60. (#1698, #894, #713).
 - TextUnformatted(): Fixed a case where large-text path would read bytes past the text_end marker depending
   on the position of new lines in the buffer (it wasn't affecting the output but still not the right thing to do!) 
+- InputTextMultiline(), RenderText(): Some optimization for very large text buffers, useful for non-optimized builds.
 - BeginMenu(): Fixed menu popup horizontal offset being off the item in the menu bar when WindowPadding=0.0f.
 - ArrowButton(): Fixed arrow shape being horizontally misaligned by (FramePadding.y-FramePadding.x) if they are different.
 - Drag and Drop: Added GetDragDropPayload() to peek directly into the payload (if any) from anywhere. (#143)

imgui.cpp

@@ -850,6 +850,7 @@ CODE
 
 #include <ctype.h>      // toupper, isprint
 #include <stdio.h>      // vsnprintf, sscanf, printf
+#include <wchar.h>      // wcslen
 #if defined(_MSC_VER) && _MSC_VER <= 1500 // MSVC 2008 or earlier
 #include <stddef.h>     // intptr_t
 #else
@@ -1210,9 +1211,7 @@ const char* ImStrchrRange(const char* str, const char* str_end, char c)
 
 int ImStrlenW(const ImWchar* str)
 {
-    int n = 0;
-    while (*str++) n++;
-    return n;
+    return (int)wcslen((const wchar_t*)str);
 }
 
 // Find end-of-line. Return pointer will point to either first \n, either str_end.

imgui_draw.cpp

@@ -2646,11 +2646,11 @@ void ImFont::RenderText(ImDrawList* draw_list, float size, ImVec2 pos, ImU32 col
     // Fast-forward to first visible line
     const char* s = text_begin;
     if (y + line_height < clip_rect.y && !word_wrap_enabled)
-        while (y + line_height < clip_rect.y)
+        while (y + line_height < clip_rect.y && s < text_end)
         {
-            while (s < text_end)
-                if (*s++ == '\n')
-                    break;
+            s = (const char*)memchr(s, '\n', text_end - s) + 1;
+            if (s == NULL)
+                s = text_end;
             y += line_height;
         }
 
@@ -2660,15 +2660,15 @@ void ImFont::RenderText(ImDrawList* draw_list, float size, ImVec2 pos, ImU32 col
     {
         const char* s_end = s;
         float y_end = y;
-        while (y_end < clip_rect.w)
+        while (y_end < clip_rect.w && s_end < text_end)
         {
-            while (s_end < text_end)
-                if (*s_end++ == '\n')
-                    break;
+            s_end = (const char*)memchr(s_end, '\n', text_end - s_end) + 1;
             y_end += line_height;
         }
         text_end = s_end;
     }
+    if (s == text_end)
+        return;
 
     // Reserve vertices for remaining worse case (over-reserving is useful and easily amortized)
     const int vtx_count_max = (int)(text_end - s) * 4;

imgui_widgets.cpp

@@ -36,6 +36,7 @@ Index of this file:
 #include "imgui_internal.h"
 
 #include <ctype.h>      // toupper, isprint
+#include <wchar.h>      // wmemchr
 #if defined(_MSC_VER) && _MSC_VER <= 1500 // MSVC 2008 or earlier
 #include <stddef.h>     // intptr_t
 #else
@@ -2906,7 +2907,7 @@ static void STB_TEXTEDIT_DELETECHARS(STB_TEXTEDIT_STRING* obj, int pos, int n)
     obj->CurLenA -= ImTextCountUtf8BytesFromStr(dst, dst + n);
     obj->CurLenW -= n;
 
-    // Offset remaining text
+    // Offset remaining text (FIXME-OPT: Use memmove)
     const ImWchar* src = obj->TextW.Data + pos + n;
     while (ImWchar c = *src++)
         *dst++ = c;
@@ -3617,8 +3618,7 @@ bool ImGui::InputTextEx(const char* label, char* buf, int buf_size, const ImVec2
             // In multi-line mode, we never exit the loop until all lines are counted, so add one extra to the searches_remaining counter.
             searches_remaining += is_multiline ? 1 : 0;
             int line_count = 0;
-            for (const ImWchar* s = text_begin; *s != 0; s++)
-                if (*s == '\n')
+            for (const ImWchar* s = text_begin; (s = (const ImWchar*)wcschr((const wchar_t*)s, (wchar_t)'\n')) != NULL; s++)
             {
                 line_count++;
                 if (searches_result_line_number[0] == -1 && s >= searches_input_ptr[0]) { searches_result_line_number[0] = line_count; if (--searches_remaining <= 0) break; }
@@ -3691,9 +3691,7 @@ bool ImGui::InputTextEx(const char* label, char* buf, int buf_size, const ImVec2
                     break;
                 if (rect_pos.y < clip_rect.y)
                 {
-                    while (p < text_selected_end)
-                        if (*p++ == '\n')
-                            break;
+                    p = (const ImWchar*)wmemchr((const wchar_t*)p, '\n', text_selected_end - p) + 1;
                 }
                 else
                 {