Barcode

The LVGL Barcode utility enables you to generate Code-128 bar codes. It uses the code128 library by fhunleth.

The LVGL Barcode utility enables you to generate Code-128 bar codes. It uses the code128 library by fhunleth.

Usage

Set LV_USE_BARCODE to 1 in lv_conf.h.

Use lv_barcode_create to create a barcode object, and use lv_barcode_update to set the data to encode.

Call lv_barcode_set_scale to adjust scaling, call lv_barcode_set_dark_color and lv_barcode_set_light_color adjust colors. Call lv_barcode_set_direction to set the bar code's orientation.

By default, LV_BARCODE_ENCODING_CODE128_GS1 encoding is used and strips [FCN1] and spaces. Optionally use lv_barcode_set_encoding to set LV_BARCODE_ENCODING_CODE128_RAW.

These can all be called in any order, before or after the data. The Widget keeps a copy of the data - costing its length in bytes - so any change, including a resize, regenerates the bars automatically.

Update mode

Every change except the colors regenerates the bars. lv_barcode_set_update_mode chooses when:

• LV_BARCODE_UPDATE_MODE_IMMEDIATE (default) regenerates inside the setter.
• LV_BARCODE_UPDATE_MODE_DEFERRED marks the bars out of date instead, so several changes collapse into one regeneration. Call lv_barcode_render when done - it regenerates from the stored data and returns the result.

lv_barcode_set_update_mode(barcode, LV_BARCODE_UPDATE_MODE_DEFERRED);
lv_barcode_set_scale(barcode, 2);
lv_barcode_set_direction(barcode, LV_DIR_VER);

lv_barcode_render(barcode);   /* generate once, here, and get the result */

Forgetting that call still gives the right bitmap - the redraw fills the bars in and warns - but the work lands on that refresh and no caller is left to see a failure.

Two things to know about deferred mode:

• The canvas is resized in the setter in both modes, because the draw pass cannot reallocate it. Only the fill is deferred.
• lv_barcode_update obeys the mode too, so in deferred mode its return value reports only the resize.

Switching back to LV_BARCODE_UPDATE_MODE_IMMEDIATE while out of date also regenerates, but that setter returns void, so a failure is only logged. Render first to get the result.

Detecting a failed regeneration

lv_barcode_render returns its result, and so does lv_barcode_update in immediate mode. The rest cannot: the property setters return void, resizes happen in an event handler, and a deferred fill happens in the draw pass. lv_barcode_is_render_valid covers those:

lv_obj_set_height(barcode, 0);   /* leaves no room for a horizontal barcode */
if(!lv_barcode_is_render_valid(barcode)) {
    /* the bitmap is blank; give the object a height */
}

It is also false before any data is set. A failure is not retried every redraw - only a change makes the Widget try again, and that change sets the flag back to true before the new attempt runs. So true means "no known failure", not "the bitmap is up to date"; in deferred mode a pending regeneration is also true.

Notes

• It is best not to manually set the width of the barcode, because when the width of the Widget is lower than the width of the barcode, the display will be incomplete due to truncation.
• A horizontal barcode is as tall as the Widget and a vertical one as wide, so that dimension must be set. Until it is, nothing can be generated - but the data is remembered, so the barcode appears once the Widget has a size.
• The scale adjustment can only be an integer multiple, for example, lv_barcode_set_scale(barcode, 2) means 2x scaling.
• The direction setting can be LV_DIR_HOR or LV_DIR_VER.
• Changing the color (dark or light) only updates the palette, so it is cheap and never regenerates the bars.

Example

Create a Barcode