updated http library to return error and response structs; updated how the GUI works to have a 'wait' UI; updated Makefile to ensure API is started before starting GUI

Makefile

@@ -16,9 +16,17 @@ RESOURCE_DIR   := $(CURDIR)/resources/dev
 GUI_ENV_FILE   ?= $(RESOURCE_DIR)/gui.env.example
 API_ENV_FILE   ?= $(RESOURCE_DIR)/api.env.example
 API_DESI_DATA  ?= $(RESOURCE_DIR)/desi_subset.json
+# The API binds here for local dev (see api/src/config.rs); `make run` passes
+# it through and waits for $(API_HEALTH_URL) to respond before launching the
+# GUI, so the renderer never races the API on startup. A bind host of
+# 0.0.0.0 is probed via 127.0.0.1. Adjust API_WAIT_TIMEOUT (seconds) if the
+# API takes longer than 60s to become healthy on a given machine.
+API_BIND_ADDR    ?= 127.0.0.1:8080
+API_HEALTH_URL   := http://$(subst 0.0.0.0,127.0.0.1,$(API_BIND_ADDR))/health
+API_WAIT_TIMEOUT ?= 60
 
 .PHONY: help setup run run-web build build-debug build-web test clean fmt \
-        renovate-validate
+        api-wait renovate-validate
 
 help: ## List available targets
 	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | \
@@ -39,9 +47,10 @@ setup: ## Setup all sub-projects (submodules, gui deps, api deps, infra deps)
 
 ## ---- Renderer (Odin) -----------------------------------------------------
 
-run: ## Run the native app (gui/)
-	@API_ENV_FILE="$(API_ENV_FILE)" API_DESI_DATA="$(API_DESI_DATA)" $(MAKE) -C $(API) run & api_pid=$$!; \
+run: ## Run the native app (gui/); waits for the API to be healthy first
+	@API_ENV_FILE="$(API_ENV_FILE)" API_DESI_DATA="$(API_DESI_DATA)" API_BIND_ADDR="$(API_BIND_ADDR)" $(MAKE) -C $(API) run & api_pid=$$!; \
 	trap 'kill $$api_pid 2>/dev/null' INT TERM EXIT; \
+	$(MAKE) api-wait || { kill $$api_pid 2>/dev/null; exit 1; }; \
 	GUI_ENV_FILE="$(GUI_ENV_FILE)" $(MAKE) -C $(GUI) run; \
 	kill $$api_pid 2>/dev/null
 
@@ -56,12 +65,28 @@ build-debug: ## Debug build (gui/ + api/)
 build-web: ## WebAssembly build -> build/web (gui/, needs emscripten)
 	@$(MAKE) -C $(GUI) build-web
 
-run-web: ## Start WASM build + API server for web dev
-	@API_ENV_FILE="$(API_ENV_FILE)" API_DESI_DATA="$(API_DESI_DATA)" $(MAKE) -C $(API) run & api_pid=$$!; \
+run-web: ## Start WASM build + API server for web dev (waits for API health)
+	@API_ENV_FILE="$(API_ENV_FILE)" API_DESI_DATA="$(API_DESI_DATA)" API_BIND_ADDR="$(API_BIND_ADDR)" $(MAKE) -C $(API) run & api_pid=$$!; \
 	trap 'kill $$api_pid 2>/dev/null' INT TERM EXIT; \
+	$(MAKE) api-wait || { kill $$api_pid 2>/dev/null; exit 1; }; \
 	GUI_ENV_FILE="$(GUI_ENV_FILE)" $(MAKE) -C $(GUI) build-web; \
 	kill $$api_pid 2>/dev/null
 
+## ---- Dev helpers ----------------------------------------------------------
+
+api-wait: ## Poll the API health endpoint until it responds (or times out)
+	@echo "Waiting for API at $(API_HEALTH_URL) ..."; \
+	elapsed=0; \
+	while ! curl -sf "$(API_HEALTH_URL)" >/dev/null 2>&1; do \
+		elapsed=$$((elapsed + 1)); \
+		if [ "$${elapsed}" -ge "$(API_WAIT_TIMEOUT)" ]; then \
+			echo "Error: API at $(API_HEALTH_URL) not healthy after $(API_WAIT_TIMEOUT)s" >&2; \
+			exit 1; \
+		fi; \
+		sleep 1; \
+	done; \
+	echo "API is up."
+
 ## ---- Aggregates ----------------------------------------------------------
 
 test: ## Test all projects (odin + cargo + go)

README.md

@@ -25,6 +25,7 @@ A fun personal project with three interlocking goals:
 Early scaffolding. The application currently:
 
 - Opens a resizable 3D raylib window with an orbital camera (zoom + rotate + pan).
+- Starts on a launch screen where you configure the API URL, pick a region, hit **Refresh catalogs** to pull the catalog list, and press **Explore** to enter the 3D view (TAB returns to the launch screen).
 - Renders a procedurally generated point cloud standing in for the galaxy catalog (real DESI data ingestion is the next milestone).
 - Compiles natively, to WebAssembly, and is deployed to an on-prem Kubernetes cluster as a placeholder web service.
 
@@ -95,6 +96,14 @@ The defaults point at `resources/dev/gui.env.example` (renderer's `API_URL`),
 `resources/dev/desi_subset.json` (a small JSON catalog subset served by the
 API's `/api/v1/catalogs` and `/api/v1/objects` endpoints).
 
+`make run` and `make run-web` start the API in the background and then wait for
+its `/health` endpoint before launching the GUI (`make api-wait`), so the
+renderer never races the API on startup. Override the bind address and worst
+case wait with `API_BIND_ADDR` (default `127.0.0.1:8080`) and
+`API_WAIT_TIMEOUT` (default 60s). The earlier you click **Refresh** on the GUI's
+launch screen, the more likely you are to catch the API mid-boot; a slow API can
+also be re-polled by pressing **Refresh** again.
+
 Project-specific targets live in their own `Makefile` and are reached with
 `make -C <dir> <target>`:
 

gui/lib/local/http/src/http.odin

@@ -7,8 +7,8 @@ import "core:strings"
 import "core:time"
 
 DEFAULT_HTTP_PORT :: 80
-MAX_REDIRECTS     :: 5
-HTTP_TIMEOUT      :: 5 * time.Second
+MAX_REDIRECTS :: 5
+HTTP_TIMEOUT :: 5 * time.Second
 
 Response :: struct {
 	status:         int,
@@ -18,42 +18,79 @@ Response :: struct {
 	chunked:        bool,
 }
 
-http_get :: proc(url: string) -> (data: string, ok: bool) {
+Error :: struct {
+	code:    int,
+	message: string,
+}
+
+Error_Code :: enum int {
+	Invalid_Url,
+	Dial_Failed,
+	Send_Failed,
+	Invalid_Response,
+	Invalid_Redirect,
+	Invalid_Chunked,
+	Too_Many_Redirects,
+}
+
+error_make :: proc(code: Error_Code) -> ^Error {
+	err := new(Error)
+	err.code = int(code)
+
+	switch code {
+	case .Invalid_Url:
+		err.message = "invalid url"
+	case .Dial_Failed:
+		err.message = "could not connect to host"
+	case .Send_Failed:
+		err.message = "could not send request"
+	case .Invalid_Response:
+		err.message = "could not parse response"
+	case .Invalid_Redirect:
+		err.message = "invalid redirect"
+	case .Invalid_Chunked:
+		err.message = "invalid chunked response"
+	case .Too_Many_Redirects:
+		err.message = "too many redirects"
+	}
+
+	return err
+}
+
+http_get :: proc(url: string) -> (resp: Response, err: ^Error) {
 	current := url
 	owns := false
 
 	for _ in 0 ..= MAX_REDIRECTS {
-		next_url, body, _, request_ok := perform_request(current)
+		next_url, next_resp, request_err := perform_request(current)
 		if owns do delete(current)
 
-		if !request_ok {
-			if next_url != "" do delete(next_url)
-			if body != "" do delete(body)
-			return "", false
+		if request_err != nil {
+			return {}, request_err
 		}
 
 		if next_url != "" {
-			if body != "" do delete(body)
 			current = next_url
 			owns = true
 			continue
 		}
 
-		return body, true
+		return next_resp, nil
 	}
 
-	return "", false
+	if owns do delete(current)
+	return {}, error_make(.Too_Many_Redirects)
 }
 
-perform_request :: proc(url: string) -> (next_url: string, body: string, status: int, ok: bool) {
+perform_request :: proc(url: string) -> (next_url: string, resp: Response, err: ^Error) {
 	host, port, path, parse_ok := parse_http_url(url)
 	if !parse_ok {
-		return "", "", 0, false
+		return "", {}, error_make(.Invalid_Url)
 	}
 
 	conn, dial_err := net.dial_tcp_from_hostname_with_port_override(host, port)
 	if dial_err != nil {
-		return "", "", 0, false
+		return "", {}, error_make(.Dial_Failed)
 	}
 	defer net.close(conn)
 
@@ -75,7 +112,7 @@ perform_request :: proc(url: string) -> (next_url: string, body: string, status:
 	)
 
 	if _, send_err := net.send_tcp(conn, transmute([]u8)request); send_err != nil {
-		return "", "", 0, false
+		return "", {}, error_make(.Send_Failed)
 	}
 
 	buf: [dynamic]u8
@@ -87,34 +124,35 @@ perform_request :: proc(url: string) -> (next_url: string, body: string, status:
 		if recv_err != nil || n == 0 do break
 	}
 
-	resp, parsed := parse_response(buf[:])
-	if !parsed {
-		return "", "", 0, false
+	parsed, response_ok := parse_response(buf[:])
+	if !response_ok {
+		return "", {}, error_make(.Invalid_Response)
 	}
+	resp = parsed
 
 	if resp.status >= 300 && resp.status < 400 && resp.location != "" {
 		resolved := resolve_redirect(url, resp.location)
 		if resolved == "" {
-			return "", "", resp.status, false
+			return "", {}, error_make(.Invalid_Redirect)
 		}
-		return resolved, "", resp.status, true
+		resp.body = ""
+		return resolved, resp, nil
 	}
 
 	if resp.chunked {
 		decoded, decode_ok := decode_chunked(resp.body)
 		if !decode_ok {
-			return "", "", resp.status, false
+			return "", {}, error_make(.Invalid_Chunked)
 		}
-		return "", decoded, resp.status, true
+		resp.body = decoded
+		return "", resp, nil
 	}
 
 	if resp.content_length >= 0 && resp.content_length < len(resp.body) {
 		resp.body = resp.body[:resp.content_length]
 	}
-	if resp.body == "" {
-		return "", "", resp.status, true
-	}
-	return "", strings.clone(resp.body), resp.status, true
+	resp.body = strings.clone(resp.body)
+	return "", resp, nil
 }
 
 parse_response :: proc(raw: []byte) -> (resp: Response, ok: bool) {
@@ -255,7 +293,7 @@ decode_chunked :: proc(data: string) -> (body: string, ok: bool) {
 	if len(decoded) == 0 {
 		return "", true
 	}
-	return string(decoded[:]), true
+	return strings.clone(string(decoded[:])), true
 }
 
 fold_eq :: proc(a, b: string) -> bool {

gui/lib/local/http/test/http_test.odin

@@ -65,11 +65,12 @@ test_http_get_request :: proc(t: ^testing.T) {
 	url := fmt.bprintf(url_buf[:], "http://127.0.0.1:%d/", bound.port)
 
 	log.infof("requesting %s", url)
-	body, ok := http.http_get(url)
-	if !testing.expect(t, ok, "http_get returned ok=false") {
+	resp, req_err := http.http_get(url)
+	if !testing.expect(t, req_err == nil, "http_get returned an error") {
 		return
 	}
-	defer delete(body)
+	defer delete(resp.body)
 
-	testing.expectf(t, body == SERVER_BODY, "expected %q, got %q", SERVER_BODY, body)
+	testing.expectf(t, resp.status == 200, "expected status 200, got %d", resp.status)
+	testing.expectf(t, resp.body == SERVER_BODY, "expected %q, got %q", SERVER_BODY, resp.body)
 }

gui/src/data.odin

@@ -1,5 +1,9 @@
 package main
 
+import "core:encoding/json"
+import "core:fmt"
+import "core:log"
+import "core:strings"
 import http "lib:http/src"
 
 Catalog :: struct {
@@ -23,30 +27,195 @@ APIError :: struct {
 	message: string,
 }
 
-get_catalogs :: proc(url: string) -> ([dynamic]Catalog, ^APIError) {
-	data, ok := http.http_get(url)
-	if !ok {
-		err := new(APIError)
-		err.code = 1
-		err.message = "request failed"
-		return nil, err
-	}
-	defer delete(data)
-
-	return nil, nil
+endpoint :: proc(base_url, path: string) -> string {
+	return fmt.tprintf("%s/%s", strings.trim_right(base_url, "/"), strings.trim_left(path, "/"))
 }
 
-get_catalog :: proc(url: string, name: string) -> (^Catalog, ^APIError) {
-	return nil, nil
+api_error :: proc(code: int, message: string) -> ^APIError {
+	err := new(APIError)
+	err.code = code
+	err.message = message
+	return err
+}
+
+destroy_api_error :: proc(err: ^APIError) {
+	delete(err.message)
+	free(err)
+}
+
+destroy_catalogs :: proc(catalogs: [dynamic]Catalog) {
+	for &c in catalogs {
+		delete(c.name)
+		delete(c.release)
+		if c.description != nil {
+			delete(c.description^)
+			free(c.description)
+		}
+		if c.object_count != nil {
+			free(c.object_count)
+		}
+	}
+	delete(catalogs)
+}
+
+destroy_catalog_objects :: proc(objects: [dynamic]CatalogObject) {
+	for &o in objects {
+		delete(o.id)
+		delete(o.catalog)
+		delete(o.object_type)
+	}
+	delete(objects)
+}
+
+request_json_array :: proc(
+	url: string,
+) -> (
+	arr: json.Array,
+	val: json.Value,
+	err: ^APIError,
+	ok: bool,
+) {
+	resp, req_err := http.http_get(url)
+	if req_err != nil {
+		defer free(req_err)
+		return nil, json.Null(nil), api_error(req_err.code, strings.clone(req_err.message)), false
+	}
+	defer delete(resp.body)
+
+	if resp.status != 200 {
+		return nil, json.Null(nil), api_error(resp.status, strings.clone(strings.trim_space(resp.body))), false
+	}
+
+	log.debugf("got %s => %s", url, resp.body)
+
+	v, perr := json.parse_string(resp.body)
+	if perr != .None {
+		return nil, json.Null(nil), api_error(int(perr), "invalid JSON in API response"), false
+	}
+
+	a, is_arr := v.(json.Array)
+	if !is_arr {
+		json.destroy_value(v)
+		return nil, json.Null(nil), api_error(0, "API response was not a JSON array"), false
+	}
+	return a, v, nil, true
+}
+
+get_catalogs :: proc(base_url: string) -> ([dynamic]Catalog, ^APIError) {
+	url := endpoint(base_url, "/api/v1/catalogs")
+	defer delete(url)
+
+	arr, val, err, ok := request_json_array(url)
+	if !ok {
+		return nil, err
+	}
+	defer json.destroy_value(val)
+
+	catalogs := make([dynamic]Catalog, 0, len(arr))
+	for item in arr {
+		if c, cat_ok := catalog_from_json(item); cat_ok {
+			append(&catalogs, c)
+		}
+	}
+	return catalogs, nil
 }
 
 get_catalog_objects :: proc(
-	url: string,
+	base_url: string,
 	catalog_name: string,
+	region: string = "",
 ) -> (
 	[dynamic]CatalogObject,
 	^APIError,
 ) {
-	return nil, nil
+	sb := strings.builder_make()
+	defer strings.builder_destroy(&sb)
+	fmt.sbprintf(&sb, "%s/api/v1/objects?catalog=%s", endpoint(base_url, ""), catalog_name)
+	if region != "" {
+		fmt.sbprintf(&sb, "&region=%s", region)
+	}
+	fmt.sbprintf(&sb, "&limit=%d", 10_000)
+	url := strings.to_string(sb)
+
+	arr, val, err, ok := request_json_array(url)
+	if !ok {
+		return nil, err
+	}
+	defer json.destroy_value(val)
+
+	objects := make([dynamic]CatalogObject, 0, len(arr))
+	for item in arr {
+		if o, obj_ok := catalog_object_from_json(item); obj_ok {
+			append(&objects, o)
+		}
+	}
+	return objects, nil
 }
 
+catalog_from_json :: proc(v: json.Value) -> (c: Catalog, ok: bool) {
+	obj, is_obj := v.(json.Object)
+	if !is_obj {
+		return {}, false
+	}
+	c = Catalog{
+		name    = json_string(obj, "name"),
+		release = json_string(obj, "release"),
+	}
+	if d, found := obj["description"]; found {
+		if s, s_ok := d.(json.String); s_ok {
+			c.description = new_clone(strings.clone(s))
+		}
+	}
+	if n, n_ok := json_u64(obj, "object_count"); n_ok {
+		c.object_count = new_clone(n)
+	}
+	return c, true
+}
+
+catalog_object_from_json :: proc(v: json.Value) -> (o: CatalogObject, ok: bool) {
+	obj, is_obj := v.(json.Object)
+	if !is_obj {
+		return {}, false
+	}
+	return CatalogObject{
+		id          = json_string(obj, "id"),
+		catalog     = json_string(obj, "catalog"),
+		object_type = json_string(obj, "object_type"),
+		ra          = json_f64(obj, "ra"),
+		dec         = json_f64(obj, "dec"),
+		redshift    = json_f64(obj, "redshift"),
+	}, true
+}
+
+json_string :: proc(obj: json.Object, key: string) -> string {
+	if v, found := obj[key]; found {
+		if s, ok := v.(json.String); ok {
+			return strings.clone(s)
+		}
+	}
+	return ""
+}
+
+json_f64 :: proc(obj: json.Object, key: string) -> f64 {
+	if v, found := obj[key]; found {
+		#partial switch n in v {
+		case json.Integer:
+			return f64(n)
+		case json.Float:
+			return n
+		}
+	}
+	return 0
+}
+
+json_u64 :: proc(obj: json.Object, key: string) -> (u64, bool) {
+	if v, found := obj[key]; found {
+		#partial switch n in v {
+		case json.Integer:
+			return u64(n), true
+		case json.Float:
+			return u64(n), true
+		}
+	}
+	return 0, false
+}

gui/src/main.odin

@@ -1,16 +1,18 @@
 package main
 
 import "base:runtime"
+import "core:fmt"
 import "core:math"
 import "core:math/rand"
 import "core:os"
+import "core:strings"
 import rl "vendor:raylib"
 
 WIDTH :: 1280
 HEIGHT :: 720
 
 // Number of procedurally generated points standing in for the DESI catalog.
-// This is replaced by real survey data once ingestion lands.
+// This is replaced by real survey data once a catalog is loaded.
 POINT_COUNT :: 4_000
 WORLD_RADIUS :: f32(500.0)
 
@@ -19,14 +21,33 @@ Galaxy :: struct {
 	color:    rl.Color,
 }
 
+Screen :: enum {
+	Start,
+	Universe,
+}
+
+App :: struct {
+	screen:           Screen,
+	api_url:          strings.Builder,
+	api_url_focused:  bool,
+	region:           strings.Builder,
+	region_focused:   bool,
+	catalogs:         [dynamic]Catalog,
+	selected_catalog: int,
+	catalog_scroll:   int,
+	status:           strings.Builder,
+	loaded_catalog:   string,
+	loaded_region:    string,
+}
+
 camera: rl.Camera3D
+app: App
 universe: [dynamic]Galaxy
 
 // Deterministic generator so the placeholder sky is stable between runs.
 rng: rand.Default_Random_State
 
 main :: proc() {
-
 	c: ^Config
 	err: ^Error
 
@@ -45,21 +66,50 @@ main :: proc() {
 	rl.SetTargetFPS(60)
 
 	camera = make_camera()
-	make_universe(&universe, POINT_COUNT)
-	defer delete(universe)
+	app = make_app(c)
+	defer destroy_app(&app)
 
 	for !rl.WindowShouldClose() {
-		update()
-		draw()
+		switch app.screen {
+		case .Start:
+			start_screen_update()
+			start_screen_draw()
+		case .Universe:
+			update()
+			draw()
+		}
 	}
 }
 
+make_app :: proc(c: ^Config) -> App {
+	a := App{
+		screen           = .Start,
+		selected_catalog = -1,
+	}
+	a.api_url = strings.builder_make()
+	a.region = strings.builder_make()
+	a.status = strings.builder_make()
+	strings.write_string(&a.api_url, c.api_url)
+	strings.write_string(&a.status, "Set the API URL, press Refresh, pick a catalog, then Explore.")
+	return a
+}
+
+destroy_app :: proc(a: ^App) {
+	strings.builder_destroy(&a.api_url)
+	strings.builder_destroy(&a.region)
+	strings.builder_destroy(&a.status)
+	destroy_catalogs(a.catalogs)
+	delete(a.loaded_catalog)
+	delete(a.loaded_region)
+	delete(universe)
+}
+
 make_camera :: proc() -> rl.Camera3D {
 	return {
-		position = {0, 220, 220},
-		target = {0, 0, 0},
-		up = {0, 1, 0},
-		fovy = 60,
+		position   = {0, 220, 220},
+		target     = {0, 0, 0},
+		up         = {0, 1, 0},
+		fovy       = 60,
 		projection = .PERSPECTIVE,
 	}
 }
@@ -73,6 +123,29 @@ make_universe :: proc(u: ^[dynamic]Galaxy, count: int) {
 	}
 }
 
+make_universe_from_objects :: proc(u: ^[dynamic]Galaxy, objects: []CatalogObject) {
+	clear(u)
+	reserve(u, len(objects))
+	for obj in objects {
+		pos := ra_dec_to_pos(f32(obj.ra), f32(obj.dec), f32(obj.redshift))
+		append(u, Galaxy{position = pos, color = color_for_position(pos)})
+	}
+}
+
+// Maps an equatorial position (ra/dec in degrees) plus redshift to a point in
+// the scene: shells telescope outward with redshift.
+ra_dec_to_pos :: proc(ra, dec, redshift: f32) -> rl.Vector3 {
+	theta := math.to_radians(ra)
+	phi := math.to_radians(dec)
+	t := math.clamp(redshift * 0.6, 0.05, 1.0)
+	r := WORLD_RADIUS * t
+	return {
+		r * math.cos(phi) * math.cos(theta),
+		r * math.sin(phi),
+		r * math.cos(phi) * math.sin(theta),
+	}
+}
+
 // Uniformly distributed random point inside the scene's bounding sphere.
 random_sphere_point :: proc(radius: f32) -> rl.Vector3 {
 	for {
@@ -97,6 +170,11 @@ color_for_position :: proc(p: rl.Vector3) -> rl.Color {
 update :: proc() {
 	// Orbital camera: drag to rotate, scroll to zoom, right-drag / shift to pan.
 	rl.UpdateCamera(&camera, .ORBITAL)
+
+	// Return to the start screen to switch catalog / region without restarting.
+	if rl.IsKeyPressed(.TAB) {
+		app.screen = .Start
+	}
 }
 
 draw :: proc() {
@@ -115,5 +193,20 @@ draw :: proc() {
 	}
 
 	rl.DrawFPS(10, 10)
-	rl.DrawText("DESI Explorer — drag to rotate, scroll to zoom", 10, 34, 18, rl.RAYWHITE)
+	ui_draw_text("DESI Explorer - drag to rotate, scroll to zoom", 10, 34, 18, rl.RAYWHITE)
+
+	buf: [128]u8
+	if app.loaded_catalog != "" {
+		ui_draw_text(fmt.bprintf(buf[:], "Catalog: %s", app.loaded_catalog), 10, 60, 18, rl.YELLOW)
+	}
+	if app.loaded_region != "" {
+		ui_draw_text(fmt.bprintf(buf[:], "Region: %s", app.loaded_region), 10, 82, 18, rl.YELLOW)
+	}
+	ui_draw_text(
+		"Press TAB to return to the start screen",
+		10,
+		i32(rl.GetScreenHeight()) - 28,
+		16,
+		{120, 120, 140, 255},
+	)
 }

gui/src/start_screen.odin

@@ -0,0 +1,196 @@
+package main
+
+import "core:fmt"
+import "core:strings"
+import rl "vendor:raylib"
+
+CATALOG_ROW_H :: 30
+
+start_screen_update :: proc() {
+	api_rect := rl.Rectangle{60, 112, 460, 34}
+	region_rect := rl.Rectangle{60, 186, 460, 34}
+
+	text_input_update(&app.api_url, &app.api_url_focused, api_rect)
+	text_input_update(&app.region, &app.region_focused, region_rect)
+
+	if ui_button_clicked(rl.Rectangle{60, 230, 170, 38}) {
+		refresh_catalogs()
+	}
+
+	list_rect := rl.Rectangle{60, 300, 520, 230}
+	if clicked := catalog_list_update(list_rect); clicked >= 0 {
+		app.selected_catalog = clicked
+		set_statusf("Selected catalog: %s", app.catalogs[clicked].name)
+	}
+
+	if ui_button_clicked(rl.Rectangle{60, 548, 150, 38}) {
+		if explore() {
+			app.screen = .Universe
+		}
+	}
+}
+
+start_screen_draw :: proc() {
+	rl.BeginDrawing()
+	defer rl.EndDrawing()
+
+	rl.ClearBackground({8, 10, 20, 255})
+
+	ui_draw_text("DESI Explorer", 60, 36, 40, rl.WHITE)
+
+	ui_draw_text("API URL", 60, 92, 16, {150, 160, 190, 255})
+	text_input_draw(&app.api_url, app.api_url_focused, rl.Rectangle{60, 112, 460, 34})
+
+	ui_draw_text("Region (optional)", 60, 166, 16, {150, 160, 190, 255})
+	text_input_draw(&app.region, app.region_focused, rl.Rectangle{60, 186, 460, 34})
+
+	ui_button(rl.Rectangle{60, 230, 170, 38}, "Refresh catalogs")
+
+	ui_draw_text("Catalogs", 60, 280, 16, {150, 160, 190, 255})
+	catalog_list_draw(rl.Rectangle{60, 300, 520, 230})
+
+	ui_button(rl.Rectangle{60, 548, 150, 38}, "Explore")
+
+	ui_draw_text(strings.to_string(app.status), 60, i32(rl.GetScreenHeight()) - 36, 16, {200, 200, 220, 255})
+}
+
+set_status :: proc(msg: string) {
+	strings.builder_reset(&app.status)
+	strings.write_string(&app.status, msg)
+}
+
+set_statusf :: proc(format: string, args: ..any) {
+	strings.builder_reset(&app.status)
+	fmt.sbprintf(&app.status, format, ..args)
+}
+
+refresh_catalogs :: proc() {
+	destroy_catalogs(app.catalogs)
+	app.catalogs = nil
+	app.selected_catalog = -1
+
+	base := strings.trim_space(strings.to_string(app.api_url))
+	if base == "" {
+		set_status("Enter an API URL first.")
+		return
+	}
+
+	catalogs, err := get_catalogs(base)
+	if err != nil {
+		set_statusf("Failed to load catalogs: %s", err.message)
+		destroy_api_error(err)
+		return
+	}
+
+	app.catalogs = catalogs
+	set_statusf("Loaded %d catalog(s). Select one and press Explore.", len(catalogs))
+}
+
+explore :: proc() -> bool {
+	if app.selected_catalog < 0 || app.selected_catalog >= len(app.catalogs) {
+		set_status("Select a catalog first.")
+		return false
+	}
+
+	base := strings.trim_space(strings.to_string(app.api_url))
+	region := strings.trim_space(strings.to_string(app.region))
+	if base == "" {
+		set_status("Enter an API URL first.")
+		return false
+	}
+
+	c := app.catalogs[app.selected_catalog]
+	objects, err := get_catalog_objects(base, c.name, region)
+	if err != nil {
+		set_statusf("Failed to load objects: %s", err.message)
+		destroy_api_error(err)
+		return false
+	}
+
+	delete(app.loaded_catalog)
+	delete(app.loaded_region)
+	app.loaded_catalog = strings.clone(c.name)
+	app.loaded_region = strings.clone(region)
+
+	if len(objects) == 0 {
+		make_universe(&universe, POINT_COUNT)
+		set_status("No objects returned - showing placeholder sky.")
+	} else {
+		make_universe_from_objects(&universe, objects[:])
+		set_statusf("Loaded %d object(s).", len(objects))
+	}
+	destroy_catalog_objects(objects)
+	return true
+}
+
+visible_row_count :: proc(rec: rl.Rectangle) -> int {
+	return max(1, int(rec.height) / CATALOG_ROW_H)
+}
+
+row_rect :: proc(rec: rl.Rectangle, index, scroll_offset: int) -> rl.Rectangle {
+	y := rec.y + f32((index - scroll_offset) * CATALOG_ROW_H)
+	return rl.Rectangle{rec.x, y, rec.width, CATALOG_ROW_H}
+}
+
+catalog_list_update :: proc(rec: rl.Rectangle) -> int {
+	mouse := rl.GetMousePosition()
+	if rl.CheckCollisionPointRec(mouse, rec) {
+		wheel := rl.GetMouseWheelMove()
+		max_scroll := max(0, len(app.catalogs) - visible_row_count(rec))
+		app.catalog_scroll = max(0, min(app.catalog_scroll - int(wheel), max_scroll))
+	}
+
+	clicked := -1
+	if len(app.catalogs) == 0 {
+		return clicked
+	}
+	visible := visible_row_count(rec)
+	for i in app.catalog_scroll ..< min(len(app.catalogs), app.catalog_scroll + visible) {
+		row := row_rect(rec, i, app.catalog_scroll)
+		if rl.CheckCollisionPointRec(mouse, row) && rl.IsMouseButtonPressed(.LEFT) {
+			clicked = i
+		}
+	}
+	return clicked
+}
+
+catalog_list_draw :: proc(rec: rl.Rectangle) {
+	rl.DrawRectangleRec(rec, {12, 14, 22, 255})
+	rl.DrawRectangleLinesEx(rec, 1, {56, 60, 82, 255})
+
+	if len(app.catalogs) == 0 {
+		ui_draw_text("No catalogs loaded - press Refresh", i32(rec.x) + 12, i32(rec.y) + 12, 16, {120, 120, 140, 255})
+		return
+	}
+
+	mouse := rl.GetMousePosition()
+	visible := visible_row_count(rec)
+	for i in app.catalog_scroll ..< min(len(app.catalogs), app.catalog_scroll + visible) {
+		row := row_rect(rec, i, app.catalog_scroll)
+		if i == app.selected_catalog {
+			rl.DrawRectangleRec(row, {44, 56, 92, 255})
+			rl.DrawRectangleLinesEx(row, 1, {120, 160, 235, 255})
+		} else if rl.CheckCollisionPointRec(mouse, row) {
+			rl.DrawRectangleRec(row, {26, 34, 56, 255})
+		}
+
+		buf: [256]u8
+		ui_draw_text(
+			catalog_display(buf[:], app.catalogs[i]),
+			i32(rec.x) + 12,
+			i32(row.y) + 6,
+			16,
+			rl.RAYWHITE,
+		)
+	}
+}
+
+catalog_display :: proc(buf: []u8, c: Catalog) -> string {
+	if c.description != nil {
+		return fmt.bprintf(buf, "%s  (%s)", c.name, c.description^)
+	}
+	if c.release != "" {
+		return fmt.bprintf(buf, "%s  (%s)", c.name, c.release)
+	}
+	return fmt.bprintf(buf, "%s", c.name)
+}

gui/src/ui.odin

@@ -0,0 +1,90 @@
+package main
+
+import c "core:c"
+import "core:strings"
+import "core:unicode/utf8"
+import rl "vendor:raylib"
+
+MAX_INPUT_LEN :: 256
+
+to_cstring_buf :: proc(buf: []u8, s: string) -> cstring {
+	n := min(len(s), len(buf) - 1)
+	copy(buf[:n], s[:n])
+	buf[n] = 0
+	return cstring(&buf[0])
+}
+
+ui_draw_text :: proc(text: string, x, y, size: c.int, color: rl.Color) {
+	buf: [1024]u8
+	rl.DrawText(to_cstring_buf(buf[:], text), x, y, size, color)
+}
+
+text_input_update :: proc(b: ^strings.Builder, focused: ^bool, rec: rl.Rectangle) {
+	mouse := rl.GetMousePosition()
+	if rl.CheckCollisionPointRec(mouse, rec) && rl.IsMouseButtonPressed(.LEFT) {
+		focused^ = true
+	} else if rl.IsMouseButtonPressed(.LEFT) {
+		focused^ = false
+	}
+
+	if !focused^ {
+		return
+	}
+
+	for r := rl.GetCharPressed(); r != 0; {
+		if len(b.buf) < MAX_INPUT_LEN {
+			strings.write_rune(b, r)
+		}
+		r = rl.GetCharPressed()
+	}
+
+	if rl.IsKeyPressed(.BACKSPACE) {
+		s := strings.to_string(b^)
+		_, rune_len := utf8.decode_last_rune(s)
+		if rune_len > 0 && len(b.buf) >= rune_len {
+			resize(&b.buf, len(b.buf) - rune_len)
+		}
+	}
+}
+
+text_input_draw :: proc(b: ^strings.Builder, focused: bool, rec: rl.Rectangle) {
+	text := strings.to_string(b^)
+
+	if focused {
+		rl.DrawRectangleRec(rec, {28, 34, 56, 255})
+		rl.DrawRectangleLinesEx(rec, 2, {90, 160, 240, 255})
+	} else {
+		rl.DrawRectangleRec(rec, {16, 18, 30, 255})
+		rl.DrawRectangleLinesEx(rec, 1, {70, 76, 96, 255})
+	}
+
+	buf: [MAX_INPUT_LEN + 1]u8
+	cstr := to_cstring_buf(buf[:], text)
+	rl.DrawText(cstr, i32(rec.x) + 8, i32(rec.y) + 8, 18, rl.RAYWHITE)
+
+	if focused {
+		cw := rl.MeasureText(cstr, 18)
+		rl.DrawRectangle(i32(rec.x) + 8 + cw + 1, i32(rec.y) + 8, 2, 20, rl.SKYBLUE)
+	}
+}
+
+ui_button_clicked :: proc(rec: rl.Rectangle) -> bool {
+	mouse := rl.GetMousePosition()
+	return rl.CheckCollisionPointRec(mouse, rec) && rl.IsMouseButtonPressed(.LEFT)
+}
+
+ui_button :: proc(rec: rl.Rectangle, label: string) {
+	mouse := rl.GetMousePosition()
+	hovered := rl.CheckCollisionPointRec(mouse, rec)
+	if hovered {
+		rl.DrawRectangleRec(rec, {48, 66, 118, 255})
+	} else {
+		rl.DrawRectangleRec(rec, {30, 38, 66, 255})
+	}
+	rl.DrawRectangleLinesEx(rec, 1, {92, 104, 134, 255})
+
+	buf: [128]u8
+	cstr := to_cstring_buf(buf[:], label)
+	w := rl.MeasureText(cstr, 18)
+	rl.DrawText(cstr, i32(rec.x) + (i32(rec.width) - w) / 2, i32(rec.y) + 10, 18, rl.RAYWHITE)
+}