Load the image from external SPI flash leads to the GUI refresh rate becomes slow

Description

What MCU/Processor/Board and compiler are you using?

STM32f407

What LVGL version are you using?

8.3

What do you want to achieve?

Store the background image into the external flash

What have you tried so far?

The background image be written into the external SPI flash because of its large size, and LVGL load the image by the fatfs. But I found, the screen refresh rate becomes slow down when the widgets upon background image need to refresh periodic. It will be OK if put the image into On-chip rom as a const array.

Code to reproduce

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