console

"exception thrown: TypeError: surfData is undefined,_SDL_FillRect@file:///Users/collinbell/taggartcybernetics/simulator/run.js:9213:14
__ZN3Sim4drawEv@file:///Users/collinbell/taggartcybernetics/simulator/run.js:18545:3
__ZN3Sim4stepEv@file:///Users/collinbell/taggartcybernetics/simulator/run.js:18756:2
__Z2cbPv@file:///Users/collinbell/taggartcybernetics/simulator/run.js:81020:3
dynCall_vi@file:///Users/collinbell/taggartcybernetics/simulator/run.js:171819:3
Runtime.dynCall@file:///Users/collinbell/taggartcybernetics/simulator/run.js:477:14
Browser_mainLoop_runner/<@file:///Users/collinbell/taggartcybernetics/simulator/run.js:6361:13
Browser.mainLoop.runIter@file:///Users/collinbell/taggartcybernetics/simulator/run.js:6425:13
Browser_mainLoop_runner@file:///Users/collinbell/taggartcybernetics/simulator/run.js:6359:9
SDL.receiveEvent@file:///Users/collinbell/taggartcybernetics/simulator/run.js:8018:15
" run.html:1245:13

"[post-exception status] Exception thrown, see JavaScript console" run.html:1245:13

TypeError: surfData is undefined run.js:9213:13
"pre-main prep time: 50 ms" hello.html:1245:13

"hello, world!" hello.html:1233:13
"Assertion failed: undefined" hello.html:1233:13
"Assertion failed: undefined" hello.html:1245:13

uncaught exception: abort("Assertion failed: undefined") at jsStackTrace@file:///Users/collinbell/taggartcybernetics/simulator/hello.js:1166:13
stackTrace@file:///Users/collinbell/taggartcybernetics/simulator/hello.js:1183:22
abort@file:///Users/collinbell/taggartcybernetics/simulator/hello.js:12241:44
assert@file:///Users/collinbell/taggartcybernetics/simulator/hello.js:357:5
_SDL_FillRect@file:///Users/collinbell/taggartcybernetics/simulator/hello.js:8188:1
_main@file:///Users/collinbell/taggartcybernetics/simulator/hello.js:8675:3
asm._main@file:///Users/collinbell/taggartcybernetics/simulator/hello.js:12029:8
callMain@file:///Users/collinbell/taggartcybernetics/simulator/hello.js:12106:15
doRun@file:///Users/collinbell/taggartcybernetics/simulator/hello.js:12164:42
run/<@file:///Users/collinbell/taggartcybernetics/simulator/hello.js:12175:7

test.cpp

#include <stdio.h>
#include <SDL/SDL.h>

#ifdef __EMSCRIPTEN__
#include <emscripten.h>
#endif

extern "C" int main(int argc, char** argv) {
printf("hello, world!\n");

SDL_Init(SDL_INIT_VIDEO);
SDL_Surface *screen = SDL_SetVideoMode(256, 256, 32, SDL_HWSURFACE);

#ifdef TEST_SDL_LOCK_OPTS
EM_ASM("SDL.defaults.copyOnLock = false; SDL.defaults.discardOnLock = true; SDL.defaults.opaqueFrontBuffer = false;");
#endif

if (SDL_MUSTLOCK(screen)) SDL_LockSurface(screen);
for (int i = 0; i < 256; i++) {
    for (int j = 0; j < 256; j++) {
#ifdef TEST_SDL_LOCK_OPTS
    // Alpha behaves like in the browser, so write proper opaque pixels.
    int alpha = 255;
#else
    int alpha = (i+j) % 255;
#endif
    //*((Uint32*)screen->pixels + i * 256 + j) = SDL_MapRGBA(screen->format, i, j, 255-i, alpha);
    }
}
SDL_Rect rect = { 200, 200, 175, 125 };
SDL_FillRect(screen, &rect, SDL_MapRGBA(screen->format, 0x22, 0x22, 0xff, 0xff));
if (SDL_MUSTLOCK(screen)) SDL_UnlockSurface(screen);
SDL_Flip(screen); 

SDL_Quit();

return 0;
}

I compile with emcc test.cpp -o hello.html