How do you manipulate these Unicode strings (how are they stored / interpreted from creation to drawing)? To avoid potential problems with compiler / text editor encodings and bad conversions, you should try it this way:
std::basic_string<sf::Uint32> str = {<codepoint>, <codepoint>, ...};
sf::String text(str);
... where <codepoint> are replaced with the Unicode value of the symbols you want to display.
EDIT: sorry I didn't notice that you were using C#... if you can't try this C++ code, you should give us the Unicode values (codepoints, or UTF-32 representation) of the characters that don't display properly, so that we can test on our side.
Works for me under Windows 10 with MinGW/GCC 4.9.2 and Arial:
(http://i.imgur.com/4PWkgdd.png)
#include <SFML/Graphics.hpp>
#include <iostream>
int main(int argc, char **argv) {
const wchar_t text[] = {0x263A, 0x263B, 0x2665, 0x2660, 0};
sf::RenderWindow window(sf::VideoMode(320, 240), "SFML Test");
sf::Font font;
if (!font.loadFromFile("arial.ttf"))
return 1;
sf::Text test(text, font, 72);
test.setColor(sf::Color::Black);
test.setPosition(50, 50);
while (window.isOpen()) {
sf::Event event;
while (window.pollEvent(event)) {
switch(event.type) {
case sf::Event::Closed:
window.close();
break;
}
}
window.clear(sf::Color::White);
window.draw(test);
window.display();
}
return 0;
}
With the Ubuntu font it indeed shows squares. However, according to Windows' Character Map tool the font doesn't include the glyphs from the test string:
0x25CA (Rhombus) is followed by 0xE0FF (custom use; here it's the Ubuntu logo). No characters between these.
Edit:
A website (like the one you linked) is no reliable verification that the font contains some specific character, because browsers will often fallback to standard fonts and/or images to render characters considered symbols or emoji (like the ones in your example).
For example, I've changed that part of the webpage's font to "Webdings" (which only includes a limited amount of picture glyps) and those characters still render fine in Edge (the text is "Hello World ☺☻♥♠"):
(http://i.imgur.com/MgjiBOu.png)