Use copied label text when the producer will reuse or release its buffer. Use static text only when the application can keep the referenced bytes valid and stable for every label reader. The word static in the API means noncopying storage; it does not extend a local variable’s lifetime or make shared scratch space safe….
Make every asset path resolve through an explicit chain: logical identifier, LVGL driver selection, callback path, backend mapping and packaged file identity. When simulator and target disagree, compare those stages before changing the image decoder. A filename that opens successfully can still identify the wrong asset copy. Applicability: this procedure pins LVGL v9.3.0 and illustrates…
A storage adapter must report two independent facts: whether an operation succeeded and how many bytes it actually transferred. A successful short read is not a complete header, and a failed seek must not become a successful read from the wrong offset. Qualify these contracts below the image decoder before diagnosing an asset-format problem. Applicability:…
A reusable custom widget needs three distinct contracts: construction establishes valid private state, event handling preserves the intended base-class behavior, and destruction releases only resources owned by that class. Add a separate readiness gate when custom initialization can fail. A constructor callback returning normally does not report that every application resource was acquired. Applicability: this…
Budget temporary drawing surfaces from their actual dimensions, format, stride and overlapping lifetimes. A small changed rectangle on the display does not establish the size of the intermediate surface used to composite a transformed widget. The useful evidence is a scene-to-layer allocation map, followed by a peak-live-surface trace. Applicability: this article pins LVGL v9.3.0 with…
Prove fallback with three pieces of evidence: the operation is declined by the accelerated draw unit, a supported alternative actually executes it, and the resulting pixels satisfy the reference. An enabled software renderer alone proves none of those things. Keep unsupported-by-every-unit cases in the test plan so missing pixels cannot masquerade as successful completion. Applicability:…
Diagnose an alpha halo by tracking what RGB means at each stage. Straight RGB stores the unattenuated color; premultiplied RGB already includes multiplication by alpha. A consumer using the wrong interpretation can darken an edge twice or add too much color. Compare known pixels over at least two backgrounds before adjusting the artwork. Applicability: this…
Use the canvas buffer’s actual format and row stride for every CPU write. Width describes visible pixels; stride describes the byte distance between row starts. They are interchangeable only in a deliberately tightly packed layout. Packed index formats also need bit selection and palette handling, so a generic bytes-per-pixel loop is not sufficient. Applicability: this…
Define Back from the user’s navigation history, not from a menu page’s current object parent. In LVGL, pages move between display containers and internal storage as navigation changes. Reusing a page or hiding its entry does not automatically establish which previous destination remains valid. Applicability: this procedure pins LVGL v9.3.0 with a main-area menu and…
Map a selected table coordinate to a logical cell owner before looking up the application action. In LVGL v9.3.0, a visually merged span does not make every touch in that span report its leading column. Custom drawing adds another identity channel: the cell currently being drawn is not necessarily the cell selected by input. Applicability:…