context by c

const char *image_context_dir[] = {"edit_image", "edit_mask", NULL};

static int /*eContextResult*/ image_context(const bContext *C,
                                            const char *member,
                                            bContextDataResult *result)
{
  SpaceImage *sima = CTX_wm_space_image(C);

  if (CTX_data_dir(member)) {
    CTX_data_dir_set(result, image_context_dir);
  }
  else if (CTX_data_equals(member, "edit_image")) {
    CTX_data_id_pointer_set(result, (ID *)ED_space_image(sima));
    return CTX_RESULT_OK;
  }
  else if (CTX_data_equals(member, "edit_mask")) {
    Mask *mask = ED_space_image_get_mask(sima);
    if (mask) {
      CTX_data_id_pointer_set(result, &mask->id);
    }
    return CTX_RESULT_OK;
  }
  return CTX_RESULT_MEMBER_NOT_FOUND;
}

struct SpaceImage *CTX_wm_space_image(const bContext *C)
{
  ScrArea *area = CTX_wm_area(C);
  if (area && area->spacetype == SPACE_IMAGE) {
    return area->spacedata.first;
  }
  return NULL;
}

/* space types, moved from DNA_screen_types.h */
/* Do NOT change order, append on end. types are hardcoded needed */
typedef enum eSpace_Type {
  SPACE_EMPTY = 0,
  ...
  SPACE_IMAGE = 6,
  ...
} eSpace_Type;

ScrArea *CTX_wm_area(const bContext *C)
{
  return ctx_wm_python_context_get(C, "area", &RNA_Area, C->wm.area);
}

extern StructRNA RNA_Area;

static void *ctx_wm_python_context_get(const bContext *C,
                                       const char *member,
                                       const StructRNA *member_type,
                                       void *fall_through)
{
#ifdef WITH_PYTHON
  if (UNLIKELY(C && CTX_py_dict_get(C))) {
    bContextDataResult result;
    memset(&result, 0, sizeof(bContextDataResult));
    BPY_context_member_get((bContext *)C, member, &result);

    if (result.ptr.data) {
      if (RNA_struct_is_a(result.ptr.type, member_type)) {
        return result.ptr.data;
      }

      CLOG_WARN(&LOG,
                "PyContext '%s' is a '%s', expected a '%s'",
                member,
                RNA_struct_identifier(result.ptr.type),
                RNA_struct_identifier(member_type));
    }
  }
#else
  UNUSED_VARS(C, member, member_type);
#endif

  /* don't allow UI context access from non-main threads */
  if (!BLI_thread_is_main()) {
    return NULL;
  }

  return fall_through;
}

bool RNA_struct_is_a(const StructRNA *type, const StructRNA *srna)
{
  const StructRNA *base;

  if (srna == &RNA_AnyType) {
    return true;
  }

  if (!type) {
    return false;
  }

  /* ptr->type is always maximally refined */
  for (base = type; base; base = base->base) {
    if (base == srna) {
      return true;
    }
  }

  return false;
}

void *CTX_py_dict_get(const bContext *C)
{
  return C->data.py_context;
}

struct bContextDataResult {
  PointerRNA ptr;
  ListBase list;
  const char **dir;
  short type; /* 0: normal, 1: seq */
};

int BPY_context_member_get(bContext *C, const char *member, bContextDataResult *result)
{
  PyObject *pyctx;
  PyObject *item;
  PointerRNA *ptr = NULL;
  bool done = false;

  pyctx = (PyObject *)CTX_py_dict_get(C);
  item = PyDict_GetItemString(pyctx, member);

  if (item == NULL) {
    /* pass */
  }
  else if (item == Py_None) {
    done = true;
  }
  else if (BPy_StructRNA_Check(item)) {
    ptr = &(((BPy_StructRNA *)item)->ptr);
    CTX_data_pointer_set(result, ptr->owner_id, ptr->type, ptr->data);
    CTX_data_type_set(result, CTX_DATA_TYPE_POINTER);
    done = true;
  }
  else if (PySequence_Check(item)) {
    PyObject *seq_fast = PySequence_Fast(item, "bpy_context_get sequence conversion");
    if (seq_fast == NULL) {
      PyErr_Print();
      PyErr_Clear();
    }
    else {
      const int len = PySequence_Fast_GET_SIZE(seq_fast);
      PyObject **seq_fast_items = PySequence_Fast_ITEMS(seq_fast);
      int i;

      for (i = 0; i < len; i++) {
        PyObject *list_item = seq_fast_items[i];

        if (BPy_StructRNA_Check(list_item)) {
          ptr = &(((BPy_StructRNA *)list_item)->ptr);
          CTX_data_list_add(result, ptr->owner_id, ptr->type, ptr->data);
        }
        else {
          CLOG_INFO(BPY_LOG_CONTEXT,
                    1,
                    "'%s' list item not a valid type in sequence type '%s'",
                    member,
                    Py_TYPE(item)->tp_name);
        }
      }
      Py_DECREF(seq_fast);
      CTX_data_type_set(result, CTX_DATA_TYPE_COLLECTION);
      done = true;
    }
  }

/typedef enum eContextResult {
  /* The context member was found, and its data is available. */
  CTX_RESULT_OK = 1,

  /* The context member was not found. */
  CTX_RESULT_MEMBER_NOT_FOUND = 0,

  /* The context member was found, but its data is not available.
   * For example, "active_bone" is a valid context member, but has not data in Object mode. */
  CTX_RESULT_NO_DATA = -1,
} eContextResult;

typedef struct ListBase {
  void *first, *last;
} ListBase;

struct bContext {
  int thread;

  /* windowmanager context */
  struct {
    struct wmWindowManager *manager;
    struct wmWindow *window;
    struct WorkSpace *workspace;
    struct bScreen *screen;
    struct ScrArea *area;
    struct ARegion *region;
    struct ARegion *menu;
    struct wmGizmoGroup *gizmo_group;
    struct bContextStore *store;
    const char *operator_poll_msg; /* reason for poll failing */
  } wm;

  /* data context */
  struct {
    struct Main *main;
    struct Scene *scene;

    int recursion;
    /** True if python is initialized. */
    bool py_init;
    void *py_context;
    /**
     * If we need to remove members, do so in a copy
     * (keep this to check if the copy needs freeing).
     */
    void *py_context_orig;
  } data;
};