C SDL2 write text to canvas segmentation fault - c

Question

I'm trying to use C to create a webassembly program to write text to an HTML5 canvas. I'm getting a segfault.
I've been looking at this tutorial: https://lyceum-allotments.github.io/2016/06/emscripten-and-sdl2-tutorial-part-6-write-owl/
This is my main.c file:
#include <stdio.h>
#include <SDL2/SDL.h>
#include <emscripten.h>
#include <stdlib.h>
#include <math.h>
#include <SDL2/SDL_ttf.h>
/**
* A Context structure that can be used to pass variables into the loop
*/
//
struct Context {
SDL_Renderer *renderer;
int iteration;
// Rectangle that texture will be rendered into
TTF_Font *font;
SDL_Texture *text_texture;
} Context;
/**
* size of the canvas in pixels
*/
const int WINDOW_WIDTH = 1600;
const int WINDOW_HEIGHT = 420;
void set_font_text(struct Context *ctx, const char *text) {
SDL_Color fg = {0,0,0,255};
SDL_Surface *text_surface = TTF_RenderText_Blended(ctx->font, text, fg);
ctx->text_texture = SDL_CreateTextureFromSurface(ctx->renderer, text_surface);
SDL_FreeSurface(text_surface);
SDL_DestroyTexture(ctx->text_texture);
}
int get_font_texture(struct Context *ctx) {
ctx->font = TTF_OpenFont("assets/fonts/Alef-Regular.ttf", 30);
set_font_text(ctx, "NEIL DU TOIT");
TTF_CloseFont(ctx->font);
TTF_Quit();
return 1;
}
/**
* The loop handler, will be called repeatedly
*/
void mainLoop(void *arg) {
struct Context *ctx = arg;
// Set background color and clear canvas
SDL_SetRenderDrawColor(ctx->renderer, 100, 143, 154, 255);
SDL_RenderClear(ctx->renderer);
SDL_Rect text_dest = {.x = 50, .y = 175, .w = 0, .h = 0};
SDL_QueryTexture(ctx->text_texture, NULL, NULL, &text_dest.w, &text_dest.h);
SDL_RenderCopy(ctx->renderer, ctx->text_texture, NULL, &text_dest);
SDL_RenderPresent(ctx->renderer);
}
int main() {
SDL_Window *window;
struct Context ctx;
SDL_Init(SDL_INIT_VIDEO);
TTF_Init();
SDL_CreateWindowAndRenderer(WINDOW_WIDTH, WINDOW_HEIGHT, 0, &window, &ctx.renderer);
SDL_SetRenderDrawColor(ctx.renderer, 255, 143, 154, 255);
get_font_texture(&ctx);
ctx.iteration = 0;
int infinite_loop = 1;
int fps = -1;
emscripten_set_main_loop_arg(mainLoop, &ctx, fps, infinite_loop);
SDL_DestroyRenderer(ctx.renderer);
SDL_DestroyWindow(window);
SDL_Quit();
}
Comiled using:
emcc main.c -s USE_SDL=2 -s WASM=1 -s USE_SDL_TTF=2 -O3 -o main.js
and served with:
python3 -m http.server 8000
When opened I immediately see:
If I remove the call to set_font_text the error goes away (but I don't see any text of course)
What's going wrong?