From e0330c1696b8fcb4b5ffb10db27410d02ea5c6d4 Mon Sep 17 00:00:00 2001
From: ocornut <omarcornut@gmail.com>
Date: Wed, 28 Sep 2022 14:54:38 +0200
Subject: [PATCH] Fonts, Text: Fixed wrapped-text not doing a fast-forward on
 lines above the clipping region. (#5720)

which would result in an abnormal number of vertices created.
---
 docs/CHANGELOG.txt |  3 +++
 imgui_draw.cpp     | 17 ++++++++++++++---
 imgui_internal.h   |  2 ++
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/docs/CHANGELOG.txt b/docs/CHANGELOG.txt
index 596448a0a..d08a9ff32 100644
--- a/docs/CHANGELOG.txt
+++ b/docs/CHANGELOG.txt
@@ -138,6 +138,9 @@ Other Changes:
 - Nav: Fixed moving/resizing window with gamepad or keyboard when running at very high framerate.
 - Nav: Pressing Space/GamepadFaceDown on a repeating button uses the same repeating rate as a mouse hold.
 - Nav: Fixed an issue opening a menu with Right key from a non-menu window.
+- Fonts, Text: Fixed wrapped-text not doing a fast-forward on lines above the clipping region,
+  which would result in an abnormal number of vertices created (was slower and more likely to
+  asserts with 16-bits ImDrawVtx). (#5720)
 - Platform IME: [Windows] Removed call to ImmAssociateContextEx() leading to freeze on some setups.
   (#2589, #5535, #5264, #4972)
 - Misc: ImGuiKey is now a typed enum, allowing ImGuiKey_XXX symbols to be named in debuggers. (#4921)
diff --git a/imgui_draw.cpp b/imgui_draw.cpp
index e7eda792b..27fcd6dbc 100644
--- a/imgui_draw.cpp
+++ b/imgui_draw.cpp
@@ -3563,11 +3563,22 @@ void ImFont::RenderText(ImDrawList* draw_list, float size, const ImVec2& pos, Im
 
     // Fast-forward to first visible line
     const char* s = text_begin;
-    if (y + line_height < clip_rect.y && !word_wrap_enabled)
+    if (y + line_height < clip_rect.y)
         while (y + line_height < clip_rect.y && s < text_end)
         {
-            s = (const char*)memchr(s, '\n', text_end - s);
-            s = s ? s + 1 : text_end;
+            const char* line_end = (const char*)memchr(s, '\n', text_end - s);
+            if (word_wrap_enabled)
+            {
+                // FIXME-OPT: This is not optimal as do first do a search for \n before calling CalcWordWrapPositionA().
+                // If the specs for CalcWordWrapPositionA() were reworked to optionally return on \n we could combine both.
+                // However it is still better than nothing performing the fast-forward!
+                s = CalcWordWrapPositionA(scale, s, line_end, wrap_width);
+                s = CalcWordWrapNextLineStartA(s, text_end);
+            }
+            else
+            {
+                s = line_end ? line_end + 1 : text_end;
+            }
             y += line_height;
         }
 
diff --git a/imgui_internal.h b/imgui_internal.h
index 427ebdece..382cd8a08 100644
--- a/imgui_internal.h
+++ b/imgui_internal.h
@@ -334,8 +334,10 @@ IMGUI_API const ImWchar*ImStrbolW(const ImWchar* buf_mid_line, const ImWchar* bu
 IMGUI_API const char*   ImStristr(const char* haystack, const char* haystack_end, const char* needle, const char* needle_end);
 IMGUI_API void          ImStrTrimBlanks(char* str);
 IMGUI_API const char*   ImStrSkipBlank(const char* str);
+IM_MSVC_RUNTIME_CHECKS_OFF
 static inline bool      ImCharIsBlankA(char c)          { return c == ' ' || c == '\t'; }
 static inline bool      ImCharIsBlankW(unsigned int c)  { return c == ' ' || c == '\t' || c == 0x3000; }
+IM_MSVC_RUNTIME_CHECKS_RESTORE
 
 // Helpers: Formatting
 IMGUI_API int           ImFormatString(char* buf, size_t buf_size, const char* fmt, ...) IM_FMTARGS(3);