How do I join up (Arabic) glyphs with SDL-TTF v2.20? - c++

Question

SDL_TTF 2.20.0 (with Harfbuzz enabled) introduced TTF_SetFontDirection() and TTF_SetFontScriptName() "for additional control over fonts using HarfBuzz".
I am trying to render some Arabic text, and I have set the font direction to RTL and the script name to "arSA\0", but the glyphs aren't joining up correctly.
Both TTF_SetFontDirection(ttf_font, TTF_DIRECTION_RTL) and TTF_SetFontScriptName(ttf_font, "arSA\0") return 0, which indicates success.
This is how I expected the text to appear:
And this is how it is appearing instead:
Can anybody tell me what I'm doing wrong?
Edit: Minimal reproducible example:
(Adapted from https://github.com/aminosbh/sdl2-ttf-sample/blob/master/src/main.c)
#include <SDL.h>
#include <SDL_ttf.h>
#include <string>
int main(int argc, char* argv[])
{
// Unused argc, argv
(void)argc;
(void)argv;
// Initialize SDL2
if (SDL_Init(SDL_INIT_VIDEO) < 0)
{
printf("SDL2 could not be initialized!\n"
"SDL2 Error: %s\n", SDL_GetError());
return 0;
}
// Initialize SDL2_ttf
TTF_Init();
// Create window
SDL_Window* window = SDL_CreateWindow("SDL2_ttf sample",
SDL_WINDOWPOS_UNDEFINED,
SDL_WINDOWPOS_UNDEFINED,
SCREEN_WIDTH, SCREEN_HEIGHT,
SDL_WINDOW_SHOWN);
if (!window)
{
printf("Window could not be created!\n"
"SDL_Error: %s\n", SDL_GetError());
}
else
{
// Create renderer
SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);
if (!renderer)
{
printf("Renderer could not be created!\n"
"SDL_Error: %s\n", SDL_GetError());
}
else
{
// Declare rect of square
SDL_Rect squareRect;
// Square dimensions: Half of the min(SCREEN_WIDTH, SCREEN_HEIGHT)
squareRect.w = MIN(SCREEN_WIDTH, SCREEN_HEIGHT) / 2;
squareRect.h = MIN(SCREEN_WIDTH, SCREEN_HEIGHT) / 2;
// Square position: In the middle of the screen
squareRect.x = SCREEN_WIDTH / 2 - squareRect.w / 2;
squareRect.y = SCREEN_HEIGHT / 2 - squareRect.h / 2;
TTF_Font* font = TTF_OpenFont(FONT_PATH, 40);
if (!font) {
printf("Unable to load font: '%s'!\n"
"SDL2_ttf Error: %s\n", FONT_PATH, TTF_GetError());
return 0;
}
const auto fontDirectionSuccess = TTF_SetFontDirection(font, TTF_DIRECTION_RTL);
const auto fontScriptNameSuccess = TTF_SetFontScriptName(font, "arSA\0");
SDL_Color textColor = { 0x00, 0x00, 0x00, 0xFF };
SDL_Color textBackgroundColor = { 0xFF, 0xFF, 0xFF, 0xFF };
SDL_Texture* text = NULL;
SDL_Rect textRect;
// Arabic text to display
const wchar_t * wstr = L"كسول الزنجبيل القط";
// Convert unicode to multibyte
int wstr_len = (int)wcslen(wstr);
int num_chars = WideCharToMultiByte(CP_UTF8, 0, wstr, wstr_len, NULL, 0, NULL, NULL);
CHAR* strTo = (CHAR*)malloc((num_chars + 1) * sizeof(CHAR));
if (strTo)
{
WideCharToMultiByte(CP_UTF8, 0, wstr, wstr_len, strTo, num_chars, NULL, NULL);
strTo[num_chars] = '\0';
}
// Render text to surface
SDL_Surface* textSurface = TTF_RenderUTF8_Blended(font, strTo, textColor);
if (!textSurface) {
printf("Unable to render text surface!\n"
"SDL2_ttf Error: %s\n", TTF_GetError());
}
else {
// Create texture from surface pixels
text = SDL_CreateTextureFromSurface(renderer, textSurface);
if (!text) {
printf("Unable to create texture from rendered text!\n"
"SDL2 Error: %s\n", SDL_GetError());
return 0;
}
// Get text dimensions
textRect.w = textSurface->w;
textRect.h = textSurface->h;
SDL_FreeSurface(textSurface);
}
textRect.x = (SCREEN_WIDTH - textRect.w) / 2;
textRect.y = squareRect.y - textRect.h - 10;
// Event loop exit flag
bool quit = false;
// Event loop
while (!quit)
{
SDL_Event e;
// Wait indefinitely for the next available event
SDL_WaitEvent(&e);
// User requests quit
if (e.type == SDL_QUIT)
{
quit = true;
}
// Initialize renderer color white for the background
SDL_SetRenderDrawColor(renderer, 0xFF, 0xFF, 0xFF, 0xFF);
// Clear screen
SDL_RenderClear(renderer);
// Draw text
SDL_RenderCopy(renderer, text, NULL, &textRect);
// Update screen
SDL_RenderPresent(renderer);
}
// Destroy renderer
SDL_DestroyRenderer(renderer);
}
// Destroy window
SDL_DestroyWindow(window);
}
// Quit SDL2_ttf
TTF_Quit();
// Quit SDL
SDL_Quit();
return 0;
}
Edit 2:
I've replaced
TTF_SetFontDirection(font, TTF_DIRECTION_RTL);
TTF_SetFontScriptName(font, "arSA\0");
with the depracated:
TTF_SetDirection(HB_DIRECTION_RTL);
TTF_SetScript(HB_SCRIPT_ARABIC);
And everything works fine. I suspect "arSA\0" might be wrong, but the only documentation I can find says it should be a "null-terminated string of exactly 4 characters", with no indication or example of which 4 characters.

Answer 1

Instead of "arSA", you should use "Arab".
See https://github.com/harfbuzz/harfbuzz/blob/7a219ca9f0f8140906cb7fd3b879b5bf5259badc/src/hb-common.h#L514
Credits to commenters "1.8e9-where's-my-share m" & "skink".
I'm adding the answer here so you can accept is as answered.