title: WebAssembly SDL example keywords:c,webassembly,js,SDL # WebAssembly SDL example ## Intro There is many examples of how to compile SDL for webassembly, but many of them isnt minimal as necessary, so here tried to make just bare minimum for application that can be compiled for 2 targets webassembly and pc. ## How things works Webassembly is virtual machine that you can run in your browser, it allows you to run compiled code. Its not 100% like real pc virtual machine and more oriented on web. But its close enough to just port and run you C/C++ or any other language that supports LLVM as backend. There need to be included emscripten header that gives callback for javascript to be runned. ```c #include ``` And as all this going to be compiled to webassembly byte code then you can _just_ load compiled file. There is many ways how wasm bytecode going to be runned. We registed our code so its runes specified number of frames per second. Check functions docs for better description. ```c void emscripten_set_main_loop(em_callback_func func, int fps, int simulate_infinite_loop) ``` Porting requiring to define loop that will be registered for webassembly engine and thats all. There need to be covered more things if there is need to use some fonts,images or files. But for now its minimal example that will draw SDL window in your browser ;] ## Source ```c #include #include #if __EMSCRIPTEN__ #include #include #include #else #include #include #endif #define SCREEN_WIDTH 200 #define SCREEN_HEIGHT 200 SDL_Window *window = NULL; SDL_Surface *screen = NULL; SDL_Surface *blank = NULL; #define MAX(a,b) ((a) > (b) ? a : b) #define MIN(a,b) ((a) < (b) ? a : b) void render() { SDL_Rect r_scr; r_scr.x = 10; r_scr.y = 20; r_scr.w = 10; r_scr.h = 10; SDL_Rect r_im; r_im.x = 0; r_im.y = 0; r_im.w = 16; r_im.h = 16; SDL_BlitSurface(blank, NULL, screen, &r_scr); } #if __EMSCRIPTEN__ void main_tick() { #else int main_tick() { #endif SDL_UpdateWindowSurface(window); #if !__EMSCRIPTEN__ return 1; #endif } void main_loop() { #if __EMSCRIPTEN__ emscripten_set_main_loop(main_tick, -1, 1); #else int quit = 0; SDL_Event event; while (quit==0) { while (SDL_PollEvent(&event)) { switch (event.type) { case SDL_QUIT: quit = 1; break; } quit = main_tick(); } printf("Loop\n"); } #endif } int main() { SDL_Init(SDL_INIT_VIDEO); window = SDL_CreateWindow( "WEBASM", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN | SDL_WINDOW_OPENGL); screen = SDL_GetWindowSurface(window); SDL_GL_SetSwapInterval(1); blank = SDL_CreateRGBSurface(0, 16, 16, 32, 0, 255, 255, 50); Uint32 color = SDL_MapRGB(blank->format, 50, 0 , 0); for (int x = 0; x < 16; x++) { for (int y = 0; y < 16; y++) { Uint32 *bufp; bufp = (Uint32 *)blank->pixels + y*blank->pitch/4 + x; *bufp = color; } } main_loop(); SDL_DestroyWindow(window); SDL_Quit(); return 0; } ``` ```js

``` ```makefile CC=gcc CFALGS= LDFLAGS=-lSDL2 -lSDL2_ttf EM_ENV=LLVM=/usr/bin NODE_JS=node EMSCRIPTEN_ROOT=/usr/lib/emscripten EM_CC=emcc EM_CFLAGS=-s WASM=1 -O3 EM_LDFALGS=-s USE_SDL=2 -s USE_SDL_IMAGE=2 -s SDL2_IMAGE_FORMATS='["png"]' -s USE_SDL_TTF=2 pc: $(CC) $(CFLAGS) $(LDFLAGS) main.c -o main em: $(EM_CC) main.c $(EM_CFLAGS) $(EM_LDFALGS) -o index.js -s EXTRA_EXPORTED_RUNTIME_METHODS='["ccall", "cwrap"]' ``` ## Links 1. https://wiki.libsdl.org/CategoryAPI 2. https://developer.mozilla.org/en-US/docs/WebAssembly/C_to_wasm 3. https://github.com/kvark/wasm-triangle/blob/master/src/main.rs 4. https://github.com/belen-albeza/space-shooter-wasm/blob/master/src/main.c 5. https://kripken.github.io/emscripten-site/docs/api_reference/emscripten.h.html