Win32 GDI and USER32 Desktop API

What is it?

This roadmap plans the first Win32 drawing and windowing APIs: GDI device contexts and bitmaps, drawing and text calls, CreateWindowExA and friends, a message loop with GetMessageA, cursors, icons and system metrics, and the standard dialogs, all built as thin wrappers over the kernel's existing graphics and window manager. Each export is tracked in the USER32 export master table. None of its eight sections has shipped, and no GDI or USER32 function exists yet.

How does it work?

Today. Nothing of the GDI or USER32 layer exists, but everything it plans to wrap does:

Drawing. gfx.h provides surfaces, rectangles, rounded rectangles, circles, lines, blits and alpha blits, described in 2D Graphics and Visual Assets. Text comes from the TrueType font manager.
Windows. wm.h creates, moves, resizes, raises, focuses and destroys windows. A window has no message queue or window procedure; input reaches it through the window manager's own callbacks. Minimize and maximize are planned in the window manager roadmap.
Cursors and icons. cursor.h has the arrow, hand, text, move, resize, wait, crosshair and forbidden shapes, and icon_store.h has 70 system icons (ICON_TOTAL_COUNT) plus icon_for_extension().
Loading Win32 programs. The PE loader in pe.c resolves imports only from kernel32.dll (14 exports) and ntdll.dll; a program that imports user32.dll or gdi32.dll cannot load. The user-mode win32.h is a small test shim, not GDI or USER32.

Planned design.

Shell icon map: Windows shell and IDI_* icon indexes mapped onto the system icons.
Device contexts: HDC and HBITMAP handles in a 256-slot table, GetDC, CreateCompatibleDC, SelectObject.
Drawing: BitBlt, Rectangle, Ellipse, LineTo and friends over gfx_*.
Text: TextOutA, DrawTextA and CreateFontA over the font manager.
Windows: CreateWindowExA, ShowWindow, DestroyWindow over wm_*.
Message loop: a per-window kernel queue with blocking GetMessageA, DispatchMessageA and DefWindowProcA.
Cursors, icons, metrics: LoadCursorA, LoadIconA, GetSystemMetrics.
Dialogs: MessageBoxA, GetOpenFileNameA and ChooseColorA forwarded to the dialog library.

flowchart LR
    APP[Win32 program] --> U32[USER32: windows, messages]
    APP --> GDI[GDI: DC, drawing, text]
    U32 --> WM[wm_* window manager]
    GDI --> GFX[gfx_* + font manager]
    U32 --> DLG[dialog library]
    U32 -.syscalls, later.-> SH[Win32k shadow SSDT]

What are its interfaces?

Interface	Status
`gfx_fill_rect()`, `gfx_draw_line()`, `gfx_blit()`, `gfx_blit_alpha()`, `ttf_draw_string()`	Shipped (wrapped primitives)
`wm_create_window()`, `wm_move_window()`, `wm_resize_window()`, `wm_focus_window()`, `wm_get_focused_window()`	Shipped (wrapped primitives)
`cursor_set_shape()`, `icon_get()`, `icon_for_extension()`	Shipped (wrapped primitives)
`GetDC()`, `CreateCompatibleDC()`, `SelectObject()`, `BitBlt()`, `TextOutA()`, `CreateFontA()`	Planned, sections 2 to 4
`CreateWindowExA()`, `ShowWindow()`, `GetMessageA()`, `DispatchMessageA()`, `RegisterClassA()`	Planned, sections 5 and 6
`LoadCursorA()`, `GetSystemMetrics()`, `MessageBoxA()`, `GetOpenFileNameA()`	Planned, sections 7 and 8

How do I use it?

Nothing is callable yet. The primitives these calls will wrap are covered by bash scripts/test.sh SUITE=desktop.

What is not implemented yet?

Win32 Shell Icon Index Map.
GDI Device Context Stubs, GDI Drawing Functions and GDI Text Functions.
USER32 Window Functions and USER32 Message Loop.
USER32 Cursor, Icon & System Metrics and USER32 Dialogs.
The kernel side of these calls, the NtGdi and NtUser system calls, is the Win32k Shadow SSDT.

How does it compare with Windows 11 and Linux?

Windows 11 implements GDI, USER32 and the common dialogs in user-mode DLLs that call into win32k.sys, with one message queue per thread. Linux has no Win32 layer of its own: native programs draw with Xlib, Cairo or GTK, and Win32 programs run through Wine's reimplementation. The plan wraps the kernel's own graphics and window manager, and gives each window its own queue instead of each thread.