Dropdown (`gsp_dropdown`)

Compact single-choice control that opens an option panel.

When to use

Use it when a common interaction is easier to express as one ready-made control.

Local interactive preview

First set up the commands from the compatibility guide, then run from an unpacked component or public repository root with gspc and gsp_sim_host:

dropdown-preview.sh

mkdir -p gsp-out/widget-preview
gspc pack \
  examples/usage/widgets/dropdown/dropdown.json \
  --deployable -o gsp-out/widget-preview/dropdown.gspb
gsp_sim_host \
  --bundle gsp-out/widget-preview/dropdown.gspb --frames 0

These commands compile the example and open it in the ESP-GSP simulator browser preview.

Runtime behavior

GSPC lowers the group to native primitives. Give an object a stable name when application code must control it.

selected is the zero-based initial index (default 0). Generated set_selected updates the active scene’s runtime selection and label, not the JSON. Restore saved selection after entering that scene. Read a clicked choice from event->arg; a getter inside the callback can still observe the value before the input transaction commits.

If application code must read or update an object, give it a stable name. GSPC then generates the typed functions listed below.

Example scene

dropdown.json

{"screen":"widget_dropdown","w":480,"h":320,"screen_bg":"#101827","font":"../../../common/fonts/DejaVuSans.ttf","font_charset":" !\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~","objects":[{"type":"dropdown","parent":-1,"name":"metric","x":70,"y":55,"w":340,"h":48,"options":["Frame throughput","Memory budget","Media decode","Input latency"],"selected":1,"open_direction":"down","font_size":16,"bg_color":"#172235","panel_color":"#1D2D44","fg_color":"#E2E8F0","border_color":"#334A68","border_width":1,"radius":10},{"type":"label","parent":-1,"x":70,"y":130,"w":340,"h":60,"text":"Tap the field, then choose an option from the panel.","font_size":16,"fg_color":"#94A3B8"}]}

The canonical example is examples/usage/widgets/dropdown/dropdown.json. Copy any relative assets referenced by the scene with it.

Generated C API

const gsp_component_directory_t *const * gsp_dropdown_docs_component_directories(uint16_t *out_count)
esp_err_t gsp_widget_dropdown___metric_label_get_effective_visible(esp_gsp_handle_t gsp, bool *out_visible)
esp_err_t gsp_widget_dropdown___metric_panel_get_effective_visible(esp_gsp_handle_t gsp, bool *out_visible)
esp_err_t gsp_widget_dropdown_metric_get_effective_visible(esp_gsp_handle_t gsp, bool *out_visible)
esp_err_t gsp_widget_dropdown_metric_get_info(esp_gsp_handle_t gsp, esp_gsp_component_info_t *out_info)
esp_err_t gsp_widget_dropdown_metric_get_selected(esp_gsp_handle_t gsp, uint32_t *out_value)
esp_err_t gsp_widget_dropdown_metric_set_selected(esp_gsp_handle_t gsp, uint32_t new_value)
esp_gsp_config_t gsp_dropdown_docs_config(void)
size_t gsp_dropdown_docs_dynamic_image_slots(void)

These signatures come from the actual compiler output for this JSON.

Fields in this example

Field	Type	Required	Default / range	Dynamic	Compiler definition
type	string	yes	—	—	widget type
parent	int	yes	default -1; -1…65534	—	parent object index (-1 = screen root)
x	int	yes	default 0; -32768…32767	scene: —; template: —	x relative to parent
y	int	yes	default 0; -32768…32767	scene: —; template: —	y relative to parent
w	int	yes	0…65535	scene: —; template: —	width in px
h	int	yes	0…65535	scene: —; template: —	height in px
name	identifier	—	—	—	stable component name; generates GSP_OBJ_KEY_<NAME>
bg_color	color	—	—	yes	dropdown background
fg_color	color	—	—	—	dropdown text color
border_color	color	—	—	—	border stroke color
border_width	int	—	0…65535	—	border stroke width
radius	int	—	default 0; 0…65535	scene: —; template: —	corner radius
font_size	int	—	1…255	—	per-object font pixel size
options	string_list	yes	—	—	option labels
open_direction	enum	—	default down; down, up	—	direction in which the option panel opens
selected	int	—	default 0; 0…65535	yes	initially selected index
panel_color	color	—	—	—	panel fill color

Show other fields supported by this Widget

Field	Type	Required	Default / range	Dynamic	Compiler definition
grow	int	—	default 0; 0…100	—	auto-layout grow weight
font	path	—	—	—	per-object TTF/OTF override
items	string_list	—	—	—	normalized dropdown option labels
item_height	int	—	0…65535	—	item row height
callback	identifier	—	—	—	selection callback
enabled	bool	—	—	—	initial interaction state; when present, exposes a runtime enabled property inherited by descendant controls
disabled_color	color	—	default #808080	—	disabled-state overlay color
disabled_opacity	int	—	default 112; 0…255	—	disabled-state overlay opacity

Show fields shared by every Widget

Field	Type	Required	Default / range	Dynamic	Compiler definition
parent_name	string	—	—	—	parent by name instead of index