move from imgui to CLAY

src/ui/ui_core.h

@@ -0,0 +1,65 @@
+#pragma once
+// ui_core.h - Thin wrapper around Clay (https://github.com/nicbarker/clay)
+// Provides Clay initialization, per-frame lifecycle, and text measurement bridging.
+
+#include "base/base_inc.h"
+#include "clay.h"
+
+////////////////////////////////
+// Text measurement callback (provided by renderer)
+// This is our app-level callback; we adapt it to Clay's signature internally.
+
+typedef Vec2F32 (*UI_MeasureTextFn)(const char *text, S32 length, F32 font_size, void *user_data);
+
+////////////////////////////////
+// UI Context
+
+struct UI_Context {
+    Clay_Context  *clay_ctx;
+    void          *clay_memory;
+
+    // Text measurement
+    UI_MeasureTextFn measure_text_fn;
+    void            *measure_text_user_data;
+};
+
+////////////////////////////////
+// Lifecycle
+
+UI_Context *ui_create(F32 viewport_w, F32 viewport_h);
+void        ui_destroy(UI_Context *ctx);
+
+// Call each frame before declaring layout
+void ui_begin_frame(UI_Context *ctx, F32 viewport_w, F32 viewport_h,
+                    Vec2F32 mouse_pos, B32 mouse_down,
+                    Vec2F32 scroll_delta, F32 dt);
+
+// Call after layout is declared; returns Clay's render command array
+Clay_RenderCommandArray ui_end_frame(UI_Context *ctx);
+
+////////////////////////////////
+// Text measurement
+
+void ui_set_measure_text_fn(UI_Context *ctx, UI_MeasureTextFn fn, void *user_data);
+
+////////////////////////////////
+// Theme colors (convenience - 0-255 Clay_Color)
+
+struct UI_Theme {
+    Clay_Color bg_dark;
+    Clay_Color bg_medium;
+    Clay_Color bg_light;
+    Clay_Color bg_lighter;
+    Clay_Color border;
+    Clay_Color text;
+    Clay_Color text_dim;
+    Clay_Color accent;
+    Clay_Color accent_hover;
+    Clay_Color title_bar;
+    Clay_Color scrollbar_bg;
+    Clay_Color scrollbar_grab;
+};
+
+extern UI_Theme g_theme;
+
+void ui_init_theme();