## Data Processing Modules

Data Processing Modules — More about data processing modules

## Run Modes

Run modes specify how a module function can be run. Data processing functions have two possible run modes.

If the function presents a (modal) dialog in which the user can for instance adjust parameter values or make selections, include `GWY_RUN_INTERACTIVE` flag in its run modes. If it makes sense to be run without asking, include `GWY_RUN_IMMEDIATE` flag in its run modes. When a function is run in immediate mode, it should fetch the last used parameter values from settings as if it is run interactively.

Many functions allow both modes and behave according to the mode they were called in. The logic typically looks as follows:

    static void
    function(GwyContainer *data, GwyRunType run)
    {
        FunctionArgs args;
        GwyDataField *data_field;
        GQuark quark;
        gboolean ok;

        /* Check run mode */
        g_return_if_fail(run & FUNCTION_RUN_MODES);

        /* Get data field to operate on */
        gwy_app_data_browser_get_current(GWY_APP_DATA_FIELD_KEY, &quark,
                                         GWY_APP_DATA_FIELD, &data_field,
                                         0);
        g_return_if_fail(data_field && quark);

        load_args(gwy_app_settings_get(), &args);

        /* Present a GUI in interactive mode, quit if cancelled */
        if (run == GWY_RUN_INTERACTIVE) {
            ok = function_dialog(&args);
            save_args(gwy_app_settings_get(), &args);
            if (!ok)
                return;
        }

        /* Perform the processing in immediate mode, or after user confirmation */
        function_do(data, data_field, quark, &args);
    }

## Masks

To highlight some areas in the data (like the grain modules do) you may want to use a mask. Masks are data fields too, differing only by a few things from the ordinary ones. Standalone masks do not exist in the container, they are always associated with some channel data. Mask data field units are irrelevant – the value range is always from 0 to 1; 0 being fully transparent and 1 the mask color set by user (may not be fully opaque). It should be noted that values different from 0 and 1 at present do not have a well-defined meaning and current modules generally produce and handle only values 0 and 1.

To attach a mask to a data field with id id, just create a new data field and put it to the container at the appropriate key which can be obtained with `gwy_app_get_mask_key_for_id()`.

    GwyDataField *mask_field;
    GQuark quark;

    mask_field = gwy_data_field_new_alike(data_field, TRUE);
    /* Fill mask_field with the mask */
    ...

    quark = gwy_app_get_mask_key_for_id(id);
    gwy_container_set_object(container, quark, mask_field);
    g_object_unref(mask_field);

If you functions takes a mask as an input (e.g., as Grain Statistics does), it should add `GWY_MENU_FLAG_DATA_MASK` to its sensitivity flags. The application will then make its menu item and/or toolbox button insensitive when no mask is available.

The mask of current channel and its key can be obtained with `gwy_app_data_browser_get_current()` as usual.

    gwy_app_data_browser_get_current(GWY_APP_MASK_FIELD, &mask_field,
                                     GWY_APP_MASK_FIELD_KEY, &quark,
                                     0);

The function will set mask_field to `NULL` and quark to 0 if the mask does not exist.

## Presentations

Presentations are means to display some data derived from channel data (or even completely unrelated data) to the user instead of the actual data, while all other processing methods and tools still can see and work on the real data. An example is Shader module.

Working with presentations is similar to masks. One only uses `gwy_app_get_show_key_for_id()` instead of `gwy_app_get_mask_key_for_id()` (most functions working with presentations have `show` in their name for `presentation` is just too long) to obtain the presentation key, and uses `GWY_APP_SHOW_FIELD` and `GWY_APP_SHOW_FIELD_KEY` when requesting the current presentation and its key. Likewise one should add `GWY_MENU_FLAG_DATA_SHOW` to menu sensitivity flags of a function which processes presentations (this is seldom needed as most functions only create presentations).

## Data Previews

Data previews in module dialogs are best realized with GwyDataView widget which is used for two-dimensional data displays everywhere else in Gwyddion. This widget is a bit complex, but we can often simplify things a lot in a module dialog. The basic scheme is following:

1. Create a local GwyContainer that will hold the objects to display. On rare occasions we can directly display data from the application's data container, but normally we are going to modify the data and therefore a local object is needed.
2. Fill it with objects. If our function does not change a data field it is easier and more efficient to just put it to the private container too, modifiable objects have to be duplicated. Since the container is private, we are free to put anything anywhere, but to take advantage of convenience data browser functions, we rather keep the application's naming scheme and make the data field the 0th channel.
3. Construct the GwyDataView. We have to put at least one layer there, namely GwyLayerBasic and set it up to display our data field. To display mask we must add GwyLayerMask too, and for interactive selections a vector layer must be added.
4. When the data of a displayed data field changes, we call `gwy_data_field_data_changed()` to notify its users.

    GtkWidget *data_view;
    GwyPixmapLayer *layer;
    GwyContainer *mydata;
    gdouble zoomval;

    /* Create new container */
    mydata = gwy_container_new();

    /* Fill it with objects and auxiliary data, dfield and id were obtained
     * before. */
    gwy_container_set_object_by_name(mydata, "/0/data", dfield);
    gwy_app_sync_data_items(data, mydata, id, 0, FALSE,
                            GWY_DATA_ITEM_PALETTE,
                            GWY_DATA_ITEM_MASK_COLOR,
                            GWY_DATA_ITEM_RANGE,
                            0);

    /* Create the data view and its layers */
    data_view = gwy_data_view_new(mydata);
    layer = gwy_layer_basic_new();
    gwy_pixmap_layer_set_data_key(layer, "/0/data");
    gwy_layer_basic_set_gradient_key(GWY_LAYER_BASIC(layer), "/0/base/palette");
    gwy_data_view_set_base_layer(GWY_DATA_VIEW(data_view), layer);

    /* Calculate preview size */
    zoomval = PREVIEW_SIZE/(gdouble)MAX(gwy_data_field_get_xres(dfield),
                                        gwy_data_field_get_yres(dfield));
    gwy_data_view_set_zoom(GWY_DATA_VIEW(data_view), zoomval);

    /* Pack data_view somewhere... */

The foregoing example uses raw data keys as `"/0/data"`. Assuming we keep the standard naming scheme we can partially avoid this with functions like `gwy_app_get_data_key_for_id()` and `g_quark_to_string()`. However, such helper functions do not exist for all objects that can appear in a container therefore some knowledge of the naming scheme is usually necessary.