To capture and save an LVGL (Light and Versatile Graphics Library) screenshot—commonly referred to in embedded systems development as an LvG-Snapshot—you must use the library’s built-in snapshot API to convert rendering data into a standard image file safely. Because microcontrollers have highly constrained RAM and flash resources, executing this process safely requires careful memory allocation to avoid device crashes. 1. Trigger the Built-In Snapshot API
Do not try to read raw display driver registers manually. Instead, use the native LVGL Snapshot Module to grab the active screen object along with all its children.
lv_snapshot_take(): Allocates a dynamic draw buffer automatically to capture the specified widget.
lv_snapshot_take_to_draw_buf(): Uses a pre-allocated buffer that you provide, which is much safer for strict memory boundaries. 2. Format the Raw Array (BMP Method)
The snapshot API returns a raw pointer (lv_image_dsc_t) or a pixel array rather than a standard image file like a PNG or JPEG. The fastest, lowest-overhead way to save this safely on an embedded processor is converting it to a BMP file:
Write a BMP Header: Prepended a standard 54-byte or 66-byte BMP file header directly ahead of your pixel data array.
Skip On-Chip Encoding: This allows your microcontroller to dump raw data straight to storage without wasting cycles on heavy compression algorithms.
Handle Color Swapping: Be sure to match your display configuration (e.g., swapping bytes from RGB to BGR or adjusting bitmasks) so the exported file looks correct on a PC. 3. Handle Storage and Memory Safely
Pre-allocate File Space: If saving to an SD card using FATFS, pre-allocate the total file size before writing to prevent time delays and buffer overflows.
Flush Hardware Caches: For high-performance microcontrollers (like STM32 or NXP i.MX RT), always flush your DMA cache (arm_dcache_flush) right after creating the snapshot to ensure memory coherence.
Free Dynamic Memory: If you used lv_snapshot_take(), call lv_draw_buf_destroy() immediately after your file write completes to release the memory back to the system pool.
Use Snipping Tool to capture screenshots – Microsoft Support
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