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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 <emscripten/emscripten.h>
```
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 <stdio.h>
#include <stdlib.h>
#if __EMSCRIPTEN__
#include <emscripten/emscripten.h>
#include <SDL2/SDL.h>
#include <SDL/SDL_ttf.h>
#else
#include <SDL2/SDL.h>
#include <SDL2/SDL_ttf.h>
#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
render();
SDL_UpdateWindowSurface(window);
#if !__EMSCRIPTEN__
return 0;
#endif
}
void main_loop()
{
#if __EMSCRIPTEN__
emscripten_set_main_loop(main_tick, -1, 1);
#else
int quit = 0;
SDL_Event event;
while (0 == quit)
{
while (SDL_PollEvent(&event))
{
quit = main_tick();
switch (event.type)
{
case SDL_QUIT:
quit = 1;
break;
}
}
}
#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, 150, 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
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body>
<script type='text/javascript'>
var Module = {};
fetch('index.wasm')
.then(response =>
response.arrayBuffer()
).then(buffer => {
Module.canvas = document.getElementById("canvas");
Module.wasmBinary = buffer;
var script = document.createElement('script');
script.src = "index.js";
script.onload = function() {
console.log("Emscripten boilerplate loaded.")
}
document.body.appendChild(script);
});
</script>
<canvas id="canvas" style="width:100%; height:100%"></canvas>
</body>
</html>
```
```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
|
