From 4f951ed0a38f9bb928b0317799ccea7b64ad5f64 Mon Sep 17 00:00:00 2001
From: juha <juha@lazarus-ide.org>
Date: Tue, 4 Sep 2018 21:58:29 +0000
Subject: [PATCH] LCL: Improvements for TWidgetSet.GetTextExtentExPoint().
 Issue #33553, patch from accorp.

git-svn-id: trunk@58863 -
---
 docs/xml/lcl/interfacebase.xml |  2 +-
 lcl/include/intfbasewinapi.inc | 76 +++++++++++++++++++++++-----------
 2 files changed, 52 insertions(+), 26 deletions(-)

diff --git a/docs/xml/lcl/interfacebase.xml b/docs/xml/lcl/interfacebase.xml
index c8624bd1a1..abcb34435f 100644
--- a/docs/xml/lcl/interfacebase.xml
+++ b/docs/xml/lcl/interfacebase.xml
@@ -3080,7 +3080,7 @@
         <short>The string containing the characters.</short>
       </element>
       <element name="TWidgetSet.GetTextExtentExPoint.Count">
-        <short>The number of logical characters in Str, -1 for automatic detection.</short>
+        <short>The number of <b>bytes</b> in Str, -1 for automatic detection.</short>
       </element>
       <element name="TWidgetSet.GetTextExtentExPoint.MaxWidth">
         <short>The maximum display width, in logical units.</short>
diff --git a/lcl/include/intfbasewinapi.inc b/lcl/include/intfbasewinapi.inc
index 2a06a1c319..ad7feb0d75 100644
--- a/lcl/include/intfbasewinapi.inc
+++ b/lcl/include/intfbasewinapi.inc
@@ -1123,44 +1123,70 @@ function TWidgetSet.GetTextExtentExPoint(DC: HDC; Str: PChar;
   Count, MaxWidth: Integer; MaxCount, PartialWidths: PInteger;
   var Size: TSize): Boolean;
 var
-  lPasStr, lCurSubStr: String;
-  lPasStrLen, i: PtrInt;
-  lCurSize: TSize;
-  lBestFitFound: Boolean = False;
+  Utf8Len, CurLen, Left, Right, I: PtrInt;
+  CurSize: TSize;
 begin
   // First obtain the size information which duplicates GetTextExtentPoint
-  Result := GetTextExtentPoint(DC,Str,Count,Size);
+  if not GetTextExtentPoint(DC, Str, Count, Size) then
+    Exit(False);
 
   if MaxCount <> nil then
-    MaxCount^ := 0;
+    MaxCount^ := 0
+  else if PartialWidths = nil then
+    Exit(True);
 
-  lPasStr := StrPas(Str);
+  if Count = 0 then
+    Exit(True);
+  if (Count < -1) or (Str = nil) then
+    Exit(False);
 
-  if (Str = nil) or (Count <= 0) or (lPasStr = '') then
-    exit(False);
+  if Count = -1 then
+    Count := Length(Str);
+  Utf8Len := UTF8Length(Str, Count);
+  if Utf8Len = 0 then
+    Exit(True);
 
-
-  // Now calculate MaxCount and PartialWidths
-  lPasStrLen := UTF8Length(lPasStr);
-  for i := 1 to lPasStrLen do
+  if PartialWidths = nil then
   begin
-    if (not lBestFitFound) then
+    if Size.cx <= MaxWidth then
+      MaxCount^ := Utf8Len
+    else
     begin
-      lCurSubStr := UTF8Copy(lPasStr, 1, i);
-      Self.GetTextExtentPoint(DC, PChar(lCurSubStr), Length(lCurSubStr), lCurSize);
-
-      // Calculate the summed partial widths
-      if PartialWidths<>nil then PartialWidths[i-1] := lCurSize.cx;
-
-      // Calculate the width until the utilized size gets bigger then the desired one
-      // Give up when the size surpases MaxWidth to be faster
-      if (MaxCount <> nil) then
+      Left := 0;
+      Right := Utf8Len;
+      while Left <= Right do
       begin
-        if lCurSize.cx <= MaxWidth then MaxCount^ := i
-        else lBestFitFound := True;
+        I := (Left + Right) div 2;
+        CurLen := UTF8CodepointToByteIndex(Str, Count, I);
+        if not GetTextExtentPoint(DC, Str, CurLen, CurSize) then
+          Exit(False);
+        if CurSize.cx <= MaxWidth then
+        begin
+          MaxCount^ := I;
+          Left := I + 1;
+        end else
+          Right := I - 1;
       end;
     end;
+  end else
+  begin
+    CurLen := 0;
+    for I := 1 to Utf8Len do
+    begin
+      Inc(CurLen, UTF8CodepointSize(@Str[CurLen]));
+      if not GetTextExtentPoint(DC, Str, CurLen, CurSize) then
+        Exit(False);
+      if MaxCount <> nil then
+      begin
+        if CurSize.cx > MaxWidth then
+          Break;
+        MaxCount^ := I;
+      end;
+      PartialWidths[I - 1] := CurSize.cx;
+    end;
   end;
+
+  Exit(True);
 end;
 
 // Note that Count is the number of bytes in the utf-8 encoded string Str