gfxlib3 preserves the existing FreeBASIC and QB graphics command surface while moving ordinary rendering and presentation onto a dedicated render thread. gfxlib2 remains the default runtime.

On Windows and Linux/X11, an ordinary mode tries Vulkan first and then OpenGL. On Linux without an X11 desktop, SDL2 can provide a KMSDRM/EGL window and OpenGL ES 3.0 renderer; the target must have SDL2's KMSDRM video driver and an EGL/GLES 3 implementation. Android uses its NativeActivity adapter and OpenGL ES 3.0 fallback. The Null backend provides deterministic headless drawing and image tests without opening a display.

The public compatibility surface includes graphics pages, palettes, the graphical console and line input, keyboard, mouse, touch and controller input, VIEW, WINDOW, PMAP, primitives, DRAW, PAINT, text, CPU images, GET, PUT, BLOAD, BSAVE, SCREENPTR, SCREENLOCK, SCREENINFO, and SCREENCONTROL.

Use the compiler option when one build setting should select gfxlib3 for unchanged source:

Source can select the same runtime before graphics declarations are loaded:

Including fbgfx3.bi also selects the runtime and declares its extension API. Do not link gfxlib2 and gfxlib3 into the same program.

The extension API can create, load, transfer, map, scale, rotate, project, and present GPU-resident surfaces. A returned surface pointer is an opaque descriptor, not pixel memory. Code that needs CPU access must use Gfx3SurfaceMap or a transfer call and must stop using the returned mapping after unmap or Screen 0.

GPU operations stay ordered with ordinary graphics commands. POINT, GET, DOWNLOAD, MAP, SCREENPTR, and CPU-only custom blenders can require a synchronization and readback boundary, so they should not be placed in a per-pixel render loop.

Renderer integrations that need a small screen rectangle can use Gfx3ScreenCapture. It fills an FB.IMAGE from the current work page, using a valid CPU shadow when available or synchronously downloading only the requested rectangle. Ordinary BASIC GET retains its reusable full-page shadow behavior.

gfxlib3 adds historical modes that gfxlib2 still leaves undefined: SCREEN 3 Hercules 720 by 348 monochrome, SCREEN 4 Olivetti/AT&T 640 by 400 monochrome, SCREEN 5 PCjr/Tandy 320 by 200 with 16 colours, and SCREEN 6 PCjr/Tandy 640 by 200 with 4 colours.