Create a fake Image if SDL_image is not available, so that we can test

stuff anyway.

src/image.cpp

@@ -40,6 +40,8 @@ private:
 
 #if defined USE_SDL
     SDL_Surface *img;
+#else
+    uint8_t *dummy;
 #endif
 };
 
@@ -67,8 +69,18 @@ Image::Image(char const *path)
     data->size = vec2i(data->img->w, data->img->h);
     data->format = data->img->format->Amask ? FORMAT_RGBA : FORMAT_RGB;
 #else
-    data->size = 0;
-    data->format = FORMAT_UNKNOWN;
+    data->size = 256;
+    data->format = FORMAT_RGBA;
+    data->dummy = (uint8_t *)malloc(256 * 256 * 4 * sizeof(*data->dummy));
+    uint8_t *parser = data->dummy;
+    for (int j = 0; j < 256; j++)
+        for (int i = 0; i < 256; i++)
+        {
+            *parser++ = ((i ^ j) & 1) * 0xff;
+            *parser++ = (uint8_t)i;
+            *parser++ = (uint8_t)j;
+            *parser++ = (((i >> 4) ^ (j >> 4)) & 1) * 0xff;
+        }
 #endif
 }
 
@@ -84,13 +96,19 @@ Image::format_t Image::GetFormat() const
 
 void * Image::GetData() const
 {
+#if defined USE_SDL
     return data->img->pixels;
+#else
+    return data->dummy;
+#endif
 }
 
 Image::~Image()
 {
-#if defined USE_LOL
+#if defined USE_SDL
     SDL_FreeSurface(data->img);
+#else
+    free(data->dummy);
 #endif
     delete data;
 }