What Is Embedded Graphics Rendering Architecture?

APP — Application and Flint-Generated Screen Code. The topmost layer — user application logic and the C code generated by Flint UI Designer. Flint generates screen descriptors: widget tree definitions, initial property values, animation descriptors, and state machine event tables. Application business logic calls Sparklet's widget API to update data properties (e.g., set a gauge value, update a text label) and registers event callbacks. No knowledge of rendering or hardware required at this layer.

WID — Widget Implementations. All 36+ widget implementations live here. Each widget manages its own state (visible, hidden, focused, pressed, animated), responds to property updates from the APP layer, generates dirty-region notifications to the GDI layer when its appearance changes, and dispatches input events (touch, encoder, key) to registered callbacks. Widgets are pure logic and geometry — they compute bounding rectangles and draw commands but never call hardware APIs directly.

GDI — Graphics Device Interface. The rendering engine. It receives draw commands from the WID layer (fill rectangle, blit image, draw text, alpha blend), maintains the dirty-region list, and routes pixel operations to either the software renderer or a hardware accelerator (DMA2D, D/AVE2D, PXP, Mali) based on platform configuration. A widget calls gdi_fill_rect() regardless of which execution path handles the fill.

EXEC — Execution Engine (Screen Manager and Frame Scheduler). The EXEC layer manages screen lifecycle: screen creation, screen switching (with transition animations), and the per-frame rendering loop. It drives the frame scheduler — on each tick it checks for pending input events, triggers state machine evaluation via RS_MIN, invokes GDI rendering for dirty regions, and initiates the framebuffer flush. In an RTOS environment, EXEC runs in a single dedicated task. In bare-metal systems, it is called from the main loop.

RS_MIN — RapidSea Minimal (State Machine and Data Engine). RS_MIN is a lightweight hierarchical state machine (HSM) engine. It evaluates UML-based state machines generated by Flint's state machine editor: state transitions, guard conditions, entry/exit actions, and event-driven property updates. RS_MIN is responsible for the "Connect" step in Flint's Design → Connect → Deploy workflow — it wires data model changes to widget property updates without requiring the developer to write event dispatch code manually. Every state machine in every Sparklet UI runs through RS_MIN each frame.

UTIL — Utilities (Codecs, Math, Memory, Fonts). The UTIL layer provides shared services used by multiple layers: PNG and JPEG image decoders, a fixed-point math library for rotation and scaling, a pool-based memory allocator suited to embedded use, and the font rasteriser (anti-aliased bitmap fonts, vector font support). The font rasteriser is the component that implements RTL text direction for right-to-left language support. No layer above UTIL needs to know which codec or math library is in use — all operations are accessed through the UTIL API.

HAL — Hardware Abstraction Layer. The HAL is the only layer with platform-specific code. It provides: display initialisation (LCD timing, framebuffer base address), framebuffer flush (DMA or sync write), touch controller read (I2C, SPI, or parallel), timer tick for the frame scheduler, and GPU or 2D accelerator initialisation and command dispatch. Porting Sparklet to a new MCU or display panel requires writing or modifying only the HAL. All six layers above compile unchanged. Platform porting services →