WebAssembly学习笔记（一）

先下载代码
cd /usr/local
git clone https://github.com/emscripten-core/emsdk.git

激活
cd emsdk
./emsdk install latest
./emsdk activate latest

设置环境变量
source ./emsdk_env.sh --build=Release

测试
$ mkdir hello
$ cd hello
$ cat << EOF > hello.cc

#include <stdio.h>
int main(int argc, char ** argv) {
  printf("Hello, world!\n");
}
EOF

编译
emcc hello.cc -o hello.html

运行
emrun --no_browser --port 8080 .
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 代码改成

// Copyright 2011 The Emscripten Authors.  All rights reserved.
// Emscripten is available under two separate licenses, the MIT license and the
// University of Illinois/NCSA Open Source License.  Both these licenses can be
// found in the LICENSE file.

#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_SWSURFACE);

#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
      // To emulate native behavior with blitting to screen, alpha component is ignored. Test that it is so by outputting
      // data (and testing that it does get discarded)
      int alpha = (i+j) % 255;
#endif
      *((Uint32*)screen->pixels + i * 256 + j) = SDL_MapRGBA(screen->format, i, j, 255-i, alpha);
    }
  }
  if (SDL_MUSTLOCK(screen)) SDL_UnlockSurface(screen);
  SDL_Flip(screen); 

  printf("you should see a smoothly-colored square - no sharp lines but the square borders!\n");
  printf("and here is some text that should be HTML-friendly: amp: |&| double-quote: |\"| quote: |'| less-than, greater-than, html-like tags: |<cheez></cheez>|\nanother line.\n");

  SDL_Quit();

  return 0;
}