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169 lines
9.8 KiB
Markdown
169 lines
9.8 KiB
Markdown
2 years ago
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# NXP
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NXP has integrated LVGL into the MCUXpresso SDK packages for several of their general purpose and crossover
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microcontrollers, allowing easy evaluation and migration into your product design.
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[Download an SDK for a supported board](https://www.nxp.com/design/software/embedded-software/littlevgl-open-source-graphics-library:LITTLEVGL-OPEN-SOURCE-GRAPHICS-LIBRARY?&tid=vanLITTLEVGL-OPEN-SOURCE-GRAPHICS-LIBRARY)
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today and get started with your next GUI application.
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## Creating new project with LVGL
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Downloading the MCU SDK example project is recommended as a starting point. It comes fully configured with LVGL (and
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with PXP/VGLite support if the modules are present), no additional integration work is required.
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## HW acceleration for NXP iMX RT platforms
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Depending on the RT platform used, the acceleration can be done by NXP PXP (PiXel Pipeline) and/or the Verisilicon GPU
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through an API named VGLite. There is a single NXP draw context that covers both GPUs allowing to have enabled either
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one or even both at the same time. While enableing both 2D accelerators, the VGLite can be used to accelerate widget
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drawing while the PXP accelerated blit and fill operations.
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Supported draw callbacks are available in "src/draw/nxp/lv_gpu_nxp.c":
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```c
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nxp_draw_ctx->base_draw.draw_arc = lv_draw_nxp_arc;
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nxp_draw_ctx->base_draw.draw_rect = lv_draw_nxp_rect;
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nxp_draw_ctx->base_draw.draw_img_decoded = lv_draw_nxp_img_decoded;
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nxp_draw_ctx->blend = lv_draw_nxp_blend;
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```
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If enabled both GPUs, the PXP is the preffered one to be used for drawing operation. A fallback mechanism is
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implemented so that if the feature is not supported by PXP (or if PXP fails), the VGLite will take over to handle the
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task. At the end, the CPU will assure that every widget drawing is fully covered (if not already done by GPU).
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### PXP accelerator
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Several drawing features in LVGL can be offloaded to the PXP engine. The VGLite (if supported) and CPU are available for
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other operations while the PXP is running. An RTOS is required to block the LVGL drawing thread and switch to another
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task or suspend the CPU for power savings.
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#### Features supported:
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- RGB565 and ARGB8888 color formats
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- Area fill + optional transparency
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- BLIT (BLock Image Transfer) + optional transparency
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- Color keying + optional transparency
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- Recoloring (color tint) + optional transparency
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- Image Rotation (90, 180, 270 degree) + optional transparency
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- Recoloring (color tint) + Image Rotation (90, 180, 270 degree) + optional transparency
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- Screen Rotation (90, 180, 270 degree)
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- RTOS integration layer
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- Default FreeRTOS and bare metal code provided
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- Combination of recolor and/or rotation + color key/alpha blend/transparency is supported but PXP needs two steps.
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First step is to recolor/rotate the image to a temporarly buffer (please check LV_MEM_SIZE value for allocation limit)
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and another step is required to handle color keying, alpha chanel or to apply transparency.
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#### Known limitations:
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- Rotation is not supported for images unaligned to blocks of 16x16 pixels.
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PXP is set to process 16x16 blocks to optimize the system for memory bandwidth and image processing time.
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The output engine essentially truncates any output pixels after the desired number of pixels has been written.
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When rotating a source image and the output is not divisible by the block size, the incorrect pixels could be truncated
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and the final output image can look shifted.
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#### Basic configuration:
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- Select NXP PXP engine in lv_conf.h: Set `LV_USE_GPU_NXP_PXP` to 1
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- Enable default implementation for interrupt handling, PXP start function and automatic initialization:
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Set `LV_USE_GPU_NXP_PXP_AUTO_INIT` to 1
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- If `SDK_OS_FREE_RTOS` symbol is defined, FreeRTOS implementation will be used, otherwise bare metal code will be
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included
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#### Basic initialization:
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- If `LV_USE_GPU_NXP_PXP_AUTO_INIT` is enabled, no user code is required; PXP is initialized automatically in
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`lv_init()`
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- For manual PXP initialization, default configuration structure for callbacks can be used. Initialize PXP before
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calling `lv_init()`
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```c
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#if LV_USE_GPU_NXP_PXP
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#include "src/draw/nxp/pxp/lv_gpu_nxp_pxp.h"
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#endif
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. . .
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#if LV_USE_GPU_NXP_PXP
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PXP_COND_STOP(!lv_gpu_nxp_pxp_init(), "PXP init failed.");
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#endif
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```
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#### Project setup:
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- Add PXP related files to project:
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- src/draw/nxp/pxp/lv_gpu_nxp_pxp.c, src/draw/nxp/pxp/lv_gpu_nxp_pxp.h: init, uninit, run/wait PXP device, log/trace
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- src/draw/nxp/pxp/lv_draw_pxp_blend.c, src/draw/nxp/pxp/lv_draw_pxp_blend.h: fill and blit (w/o transformation)
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- src/draw/nxp/pxp/lv_gpu_nxp_osa.c, src/draw/nxp/pxp/lv_gpu_osa.h: default implementation of OS-specific functions
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(bare metal and FreeRTOS only)
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- optional, required only if `LV_USE_GPU_NXP_PXP_AUTO_INIT` is set to 1
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- PXP related code depends on two drivers provided by MCU SDK. These drivers need to be added to project:
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- fsl_pxp.c, fsl_pxp.h: PXP driver
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- fsl_cache.c, fsl_cache.h: CPU cache handling functions
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#### Logging:
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- By default, LV_GPU_NXP_PXP_LOG_ERRORS is enabled so that any PXP error will be seen on LVGL output
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- For tracing logs about the PXP limitations or size thresholds, the user can enable LV_GPU_NXP_PXP_LOG_TRACES
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#### Advanced configuration:
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- Implementation depends on multiple OS-specific functions. The struct `lv_nxp_pxp_cfg_t` with callback pointers is
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used as a parameter for the `lv_gpu_nxp_pxp_init()` function. Default implementation for FreeRTOS and baremetal is
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provided in lv_gpu_nxp_osa.c
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- `pxp_interrupt_init()`: Initialize PXP interrupt (HW setup, OS setup)
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- `pxp_interrupt_deinit()`: Deinitialize PXP interrupt (HW setup, OS setup)
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- `pxp_run()`: Start PXP job. Use OS-specific mechanism to block drawing thread. PXP must finish drawing before
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leaving this function.
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- There are configurable area thresholds which are used to decide whether the area will be processed by CPU or by PXP.
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Areas smaller than a defined value will be processed by CPU and those bigger than the threshold will be processed by
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PXP. These thresholds may be defined as preprocessor variables. Default values are defined in lv_draw_pxp_blend.h
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- `LV_GPU_NXP_PXP_BLIT_SIZE_LIMIT`: size threshold for image BLIT, BLIT with color keying, BLIT with recolor and
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BLIT with rotation (OPA >= LV_OPA_MAX)
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- `LV_GPU_NXP_PXP_BLIT_OPA_SIZE_LIMIT`: size threshold for image BLIT, BLIT with color keying, BLIT with recolor
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and BLIT with rotation and transparency (OPA < LV_OPA_MAX)
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- `LV_GPU_NXP_PXP_FILL_SIZE_LIMIT`: size threshold for fill operation (OPA >= LV_OPA_MAX)
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- `LV_GPU_NXP_PXP_FILL_OPA_SIZE_LIMIT`: size threshold for fill operation with transparency (OPA < LV_OPA_MAX)
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### VGLite accelerator
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Extra drawing features in LVGL can be handled by the VGLite engine. The PXP (if supported) and CPU are available for
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other operations while the VGLite is running. An RTOS is required to block the LVGL drawing thread and switch to another
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task or suspend the CPU for power savings.
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#### Features supported:
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- RGB565 and ARGB8888 color formats
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- Area fill + optional transparency
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- BLIT (BLock Image Transfer) + optional transparency
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- Image Rotation (any degree with decimal) + optional transparency
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- Image Scale + optional transparency
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- Draw background rectangle with radius or gradient
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- Draw arc
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- RTOS integration layer
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#### Basic configuration:
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- Select NXP VGLite engine in lv_conf.h: Set `LV_USE_GPU_NXP_VG_LITE` to 1
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- `SDK_OS_FREE_RTOS` symbol needs to be defined so that the FreeRTOS implementation will be used
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#### Basic initialization:
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- Initialize VGLite before calling `lv_init()` by specifying the width/height of tessellation window. Value should be
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a multiple of 16; minimum value is 16 pixels, maximum cannot be greater than frame width. If less than or equal to 0,
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then no tessellation buffer is created, in which case the function is used for a blit init.
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```c
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#if LV_USE_GPU_NXP_VG_LITE
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#include "vg_lite.h"
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#endif
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. . .
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#if LV_USE_GPU_NXP_VG_LITE
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VG_LITE_COND_STOP(vg_lite_init(64, 64) != VG_LITE_SUCCESS, "VGLite init failed.");
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#endif
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```
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#### Project setup:
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- Add VGLite related files to project:
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- src/draw/nxp/vglite/lv_gpu_nxp_vglite.c, src/draw/nxp/vglite/lv_gpu_nxp_vglite.h: buffer init, log/trace
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- src/draw/nxp/vglite/lv_draw_vglite_blend.c, src/draw/nxp/vglite/lv_draw_vglite_blend.h: fill and blit
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(w/o transformation)
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- src/draw/nxp/vglite/lv_draw_vglite_rect.c, src/draw/nxp/vglite/lv_draw_vglite_rect.h: rectangle draw
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- src/draw/nxp/vglite/lv_draw_vglite_arc.c, src/draw/nxp/vglite/lv_draw_vglite_arc.h: arc draw
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#### Logging:
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- By default, LV_GPU_NXP_VG_LITE_LOG_ERRORS is enabled so that any VGLite error will be seen on LVGL output
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- For tracing logs about the VGLite limitations, size thresholds or stride alignment, the user can enable
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LV_GPU_NXP_VG_LITE_LOG_TRACES
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#### Advanced configuration:
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- There are configurable area thresholds which are used to decide whether the area will be processed by CPU or by
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VGLite. Areas smaller than a defined value will be processed by CPU and those bigger than the threshold will be
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processed by VGLite. These thresholds may be defined as preprocessor variables. Default values are defined in
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lv_draw_vglite_blend.h
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- `LV_GPU_NXP_VG_LITE_BLIT_SIZE_LIMIT`: size threshold for image BLIT, BLIT with scale and BLIT with rotation
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(OPA >= LV_OPA_MAX)
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- `LV_GPU_NXP_VG_LITE_BLIT_OPA_SIZE_LIMIT`: size threshold for image BLIT, BLIT with scale and BLIT with rotation
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and transparency (OPA < LV_OPA_MAX)
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- `LV_GPU_NXP_VG_LITE_FILL_SIZE_LIMIT`: size threshold for fill operation (OPA >= LV_OPA_MAX)
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- `LV_GPU_NXP_VG_LITE_FILL_OPA_SIZE_LIMIT`: size threshold for fill operation with transparency (OPA < LV_OPA_MAX)
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