VG-Lite General GPU（VG-Lite通用GPU）

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This is a generic VG-Lite rendering backend implementation that is designed to utilize VeriSilicon's generic API to operate GPU hardware as much as possible.

Even with different chip manufacturers, as long as they use the same version of VG-Lite API as the rendering backend, LVGL rendering acceleration can be supported without the need for LVGL adaptation work.

这是一个通用的VG-Lite渲染后端实现，旨在尽可能利用 VeriSilicon 的通用API来操作GPU硬件。

即使不同的芯片制造商，只要他们使用与渲染后端相同版本的VG-Lite API，LVGL渲染加速就可以得到支持，无需对LVGL进行适配工作。

Configuration（配置）

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1. Set LV_USE_DRAW_VG_LITE to 1 in lv_conf.h to enabled the VG-Lite rendering backend. Make sure that your hardware has been adapted to the VG-Lite API and that the absolute path to vg_lite.h, which can be directly referenced by lvgl, has been exposed.

2. Confirm the GPU initialization method, there are two ways: - The SDK calls the GPU initialization function on its own during system startup, and the GPU is available when LVGL starts; set LV_VG_LITE_USE_GPU_INIT to 0. - LVGL actively calls the GPU initialization function, and the SDK needs to implement the public function gpu_init().

LVGL will call it to complete the GPU hardware initialization during startup; set LV_VG_LITE_USE_GPU_INIT to 1.

3. Set the LV_VG_LITE_USE_ASSERT configuration to enable GPU call parameter checking. Due to the complexity of the parameters used in GPU calls, incorrect parameters can result in abnormal GPU hardware operation, such as forgetting to add an end symbol to the path or not meeting the alignment requirements for buffer stride. To quickly resolve such issues, strict parameter checking has been added before each VG-Lite call, including buffer stride validation and matrix invertibility check. When an error parameter is detected, an assertion will occur to print out the error parameter, allowing the user to promptly make corrections and reduce the time wasted on hardware simulation. Please note that enabling this check will decrease runtime performance. It is recommended to enable it in Debug mode and disable it in the Release version.

4. Set the LV_VG_LITE_FLUSH_MAX_COUNT configuration to specify the flush method. VG-Lite uses two sets of command buffer buffers to render instructions, and utilizing this mechanism well can greatly improve drawing efficiency. Currently, two buffering methods are supported: - Set LV_VG_LITE_FLUSH_MAX_COUNT to zero (recommended). The rendering backend will obtain the GPU's working status every time it writes rendering instructions to the command buffer. When the GPU is idle, it will immediately call vg_lite_flush to notify the GPU to start rendering and swap the command buffer. When the GPU is busy, it will continue to fill the command buffer cache with rendering instructions. The underlying driver will automatically determine if the command buffer has been filled. When it is about to be filled, it will forcibly wait for the unfinished drawing tasks to end and swap the command buffer. This method can effectively improve GPU utilization, especially in scenarios where rendering text, as the GPU's drawing time and the CPU's data preparation time are very close, allowing the CPU and GPU to run in parallel. - Set LV_VG_LITE_FLUSH_MAX_COUNT to a value greater than zero, such as 8. After writing 8 rendering instructions to the command buffer, the rendering backend will call vg_lite_flush to notify the GPU to start rendering and swap the command buffer.

5. Set the LV_VG_LITE_USE_BOX_SHADOW configuration to use GPU rendering for shadows. In fact, GPU hardware does not actually support shadow rendering. However, through experimentation, it has been found that a similar shadow effect can be achieved by using multiple layers of borders with different levels of transparency. It is recommended to enable this configuration in scenarios where the shadow quality requirements are not high, as it can significantly improve rendering efficiency.

6. Set the LV_VG_LITE_GRAD_CACHE_CNT configuration to specify the number of gradient cache entries. Gradient drawing includes linear gradients and radial gradients. Using a cache can effectively reduce the number of times the gradient image is created and improve drawing efficiency. Each individual gradient consumes around 4K of GPU memory pool. If there are many gradients used in the interface, you can try increasing the number of gradient cache entries. If the VG-Lite API returns the VG_LITE_OUT_OF_RESOURCES error, you can try increasing the size of the GPU memory pool or reducing the number of gradient cache entries.

7. Set the LV_VG_LITE_STROKE_CACHE_CNT configuration to specify the number of stroke path caches. When the stroke parameters do not change, the previously generated stroke parameters are automatically retrieved from the cache to improve rendering performance. The memory occupied by the stroke is strongly related to the path length. If the VG-Lite API returns the VG_LITE_OUT_OF_RESOURCES error, you can try increasing the size of the GPU memory pool or reducing the number of stroke cache entries.

NOTE: VG-Lite rendering backend does not support multi-threaded calls, please make sure LV_USE_OS is always configured as LV_OS_NONE.

1. 在 lv_conf.h 中将 LV_USE_DRAW_VG_LITE 设置为1以启用VG-Lite渲染后端。确保您的硬件已经适配VG-Lite API，并且已经暴露可以直接被lvgl引用的 vg_lite.h 的绝对路径。

2. 确认GPU初始化方法，有两种方式： - SDK在系统启动期间自行调用GPU初始化函数，LVGL启动时GPU已经可用；将 LV_VG_LITE_USE_GPU_INIT 设置为0。 - LVGL主动调用GPU初始化函数，SDK需要实现公共函数 gpu_init()。 LVGL将在启动期间调用它来完成GPU硬件初始化；将 LV_VG_LITE_USE_GPU_INIT 设置为1。

3. 设置 LV_VG_LITE_USE_ASSERT 配置以启用GPU调用参数检查。由于GPU调用中使用的参数复杂，错误的参数可能导致GPU硬件异常操作，例如忘记在路径中添加结束符号或不满足缓冲区步长的对齐要求。为了快速解决这类问题，在每次VG-Lite调用前增加了严格的参数检查，包括缓冲区步长验证和矩阵可逆性检查。当检测到错误的参数时，将触发断言并打印出错误参数，允许用户及时进行更正，减少在硬件模拟上浪费的时间。请注意，启用此检查将降低运行时性能。建议在Debug模式下启用它，在Release版本中禁用它。

4. 将 LV_VG_LITE_FLUSH_MAX_COUNT 配置以指定刷新方法。 VG-Lite使用两组命令缓冲区来渲染指令，充分利用这一机制可以大大提高绘图效率。目前支持两种缓冲方法： - 将 LV_VG_LITE_FLUSH_MAX_COUNT 设置为零（推荐）。渲染后端每次向命令缓冲区写入渲染指令时，都会获取GPU的工作状态。当GPU空闲时，它将立即调用 vg_lite_flush 通知GPU开始渲染并交换命令缓冲区。当GPU忙碌时，它将继续用渲染指令填充命令缓冲区缓存。底层驱动程序将自动判断命令缓冲区是否已被填充。当即将被填满时，它将强制等待未完成的绘图任务结束并交换命令缓冲区。这种方法可以有效地提高GPU利用率，特别是在渲染文本的场景中，因为GPU的绘图时间和CPU的数据准备时间非常接近，允许CPU和GPU并行运行。 - 将 LV_VG_LITE_FLUSH_MAX_COUNT 设置为大于零的值，例如8。在向命令缓冲区写入8个渲染指令后，渲染后端将调用 vg_lite_flush 通知GPU开始渲染并交换命令缓冲区。

5. 设置 LV_VG_LITE_USE_BOX_SHADOW 配置以使用GPU渲染阴影。实际上，GPU硬件并不真正支持阴影渲染。然而，通过实验发现，通过使用具有不同透明度级别的多层边框，可以实现类似的阴影效果。建议在阴影质量要求不高的场景中启用此配置，因为它可以显著提高渲染效率。

6. 设置 LV_VG_LITE_GRAD_CACHE_CNT 配置以指定渐变缓存条目数。渐变绘制包括线性渐变和径向渐变。使用缓存可以有效地减少创建渐变图像的次数，提高绘图效率。每个单独的渐变大约消耗4K的GPU内存池。如果界面中使用了很多渐变，可以尝试增加渐变缓存条目数。如果VG-Lite API返回 VG_LITE_OUT_OF_RESOURCES 错误，可以尝试增加GPU内存池的大小或减少渐变缓存条目数。

7. 设置 LV_VG_LITE_STROKE_CACHE_CNT 配置以指定笔触路径缓存的数量。当笔触参数不变时，自动从缓存中检索先前生成的笔触参数以提高渲染性能。笔触占用的内存与路径长度密切相关。如果VG-Lite API返回 VG_LITE_OUT_OF_RESOURCES 错误，可以尝试增加GPU内存池的大小或减少笔触缓存条目数。

注意：VG-Lite渲染后端不支持多线程调用，请确保 LV_USE_OS 始终配置为 LV_OS_NONE。

VG-Lite Simulator（VG-Lite模拟器）

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LVGL integrates a VG-Lite simulator based on ThorVG. Its purpose is to simplify the debugging of VG-Lite adaptation and reduce the time of debugging and locating problems on hardware devices. For detailed instructions, see VG-Lite Simulator.

LVGL集成了一个基于ThorVG的VG-Lite模拟器。它的目的是简化VG-Lite适配的调试，并减少在硬件设备上调试和定位问题的时间。详细说明，请参见 VG-Lite Simulator 。