Correctly draw cursor based on position.

Had to add UTF-8 functions utf8_length, utf8_next, utf8_advance.

test/testime.c

@@ -26,6 +26,48 @@ SDL_Rect textRect, markedRect;
 Uint32 lineColor, backColor;
 SDL_Color textColor = { 0, 0, 0 };
 char text[MAX_TEXT_LENGTH], markedText[SDL_TEXTEDITINGEVENT_TEXT_SIZE];
+int cursor = 0;
+
+size_t utf8_length(unsigned char c)
+{
+    c = (unsigned char)(0xff & c);
+    if (c < 0x80)
+        return 1;
+    else if ((c >> 5) ==0x6)
+        return 2;
+    else if ((c >> 4) == 0xe)
+        return 3;
+    else if ((c >> 3) == 0x1e)
+        return 4;
+    else
+        return 0;
+}
+
+char *utf8_next(char *p)
+{
+    size_t len = utf8_length(*p);
+    size_t i = 0;
+    if (!len)
+        return 0;
+
+    for (; i < len; ++i)
+    {
+        ++p;
+        if (!*p)
+            return 0;
+    }
+    return p;
+}
+
+char *utf8_advance(char *p, size_t distance)
+{
+    size_t i = 0;
+    for (; i < distance && p; ++i)
+    {
+        p = utf8_next(p);
+    }
+    return p;
+}
 
 void usage()
 {
@@ -181,6 +223,19 @@ void Redraw()
     if (markedText[0])
     {
 #ifdef HAVE_SDL_TTF
+        if (cursor)
+        {
+            char *p = utf8_advance(markedText, cursor);
+            char c = 0;
+            if (!p)
+                p = &markedText[strlen(markedText)];
+
+            c = *p;
+            *p = 0;
+            TTF_SizeUTF8(font, markedText, &w, 0);
+            cursorRect.x += w;
+            *p = c;
+        }
         RenderText(screen, font, markedText, markedRect.x, markedRect.y, textColor);
         TTF_SizeUTF8(font, markedText, &w, &h);
 #endif
@@ -190,8 +245,6 @@ void Redraw()
         underlineRect.h = 2;
         underlineRect.w = w;
 
-        cursorRect.x += w + 1;
-
         SDL_FillRect(screen, &underlineRect, lineColor);
     }
 
@@ -308,6 +361,7 @@ int main(int argc, char *argv[])
                     event.edit.text, event.edit.start, event.edit.length);
 
             strcpy(markedText, event.edit.text);
+            cursor = event.edit.start;
             Redraw();
             break;