test/browser/test_sdl2_canvas_write.c

// Copyright 2015 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 <assert.h>
#include <SDL.h>
#include <emscripten/em_asm.h>

static void sdlError(const char* str) {
  fprintf(stderr, "Error at %s: %s\n", str, SDL_GetError());
  exit(1);
}

void draw(SDL_Window* window, SDL_Surface* surface) {
  int x, y;

  if (SDL_MUSTLOCK(surface)) {
    if (SDL_LockSurface(surface) != 0)
      sdlError("SDL_LockSurface");
  }

  for (y = 0; y < 256; y++) {
    Uint32* p = (Uint32*)(((Uint8*)surface->pixels) + surface->pitch * y);
    for (x = 0; x < 256; x++) {
      *(p++) = SDL_MapRGB(surface->format, x, x ^ y, y);
    }
  }

  if (SDL_MUSTLOCK(surface))
    SDL_UnlockSurface(surface);
  if (SDL_UpdateWindowSurface(window) != 0)
    sdlError("SDL_UpdateWindowSurface");
}

void verify(void) {
  int res = EM_ASM_INT({
    var ctx = Module['canvas'].getContext('2d');
    var data = ctx.getImageData(0, 0, 256, 256).data;
    var idx = 0;
    for (var y = 0; y < 256; y++) {
        for (var x = 0; x < 256; x++) {
            if (data[idx    ] !== x || 
                data[idx + 1] !== (x ^ y) || 
                data[idx + 2] !== y ||
                data[idx + 3] !== 255) {
                return 1;
            }
            idx += 4;
        }
    }
    return 0;
  });

  printf("%s\n", res ? "FAIL" : "PASS");
  assert(res == 0);
}

int main(void) {
  SDL_Window* window;
  SDL_Surface* surface;

  if (SDL_Init(SDL_INIT_VIDEO) != 0)
    sdlError("SDL_Init");

  window = SDL_CreateWindow("SDL2 test", 0, 0, 256, 256, SDL_WINDOW_SHOWN);
  if (window == NULL) {
    sdlError("SDL_CreateWindow");
  }
  surface = SDL_GetWindowSurface(window);
  if (surface == NULL)  {
    sdlError("SDL_GetWindowSurface");
  }

  draw(window, surface);

  verify();
  return 0;
}