【LittlevGL】看看LVGL8的draw |
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【LittlevGL】看看LVGL8的draw
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调用"lv_disp_drv_init"函数初始化一个显示设备驱动，一个显示设备驱动的结构体内容如下： typedef struct _lv_disp_drv_t { lv_coord_t hor_res; /**< Horizontal resolution.*/ lv_coord_t ver_res; /**< Vertical resolution.*/ lv_coord_t physical_hor_res; /**< Horizontal resolution of the full / physical display. Set to -1 for fullscreen mode.*/ lv_coord_t physical_ver_res; /**< Vertical resolution of the full / physical display. Set to -1 for fullscreen mode.*/ lv_coord_t offset_x; /**< Horizontal offset from the full / physical display. Set to 0 for fullscreen mode.*/ lv_coord_t offset_y; /**< Vertical offset from the full / physical display. Set to 0 for fullscreen mode.*/ /** Pointer to a buffer initialized with `lv_disp_draw_buf_init()`. * LVGL will use this buffer(s) to draw the screens contents*/ lv_disp_draw_buf_t * draw_buf; uint32_t direct_mode : 1; /**< 1: Use screen-sized buffers and draw to absolute coordinates*/ uint32_t full_refresh : 1; /**< 1: Always make the whole screen redrawn*/ uint32_t sw_rotate : 1; /**< 1: use software rotation (slower)*/ uint32_t antialiasing : 1; /**< 1: anti-aliasing is enabled on this display.*/ uint32_t rotated : 2; /**< 1: turn the display by 90 degree. @warning Does not update coordinates for you!*/ uint32_t screen_transp : 1; /**Handle if the screen doesn't have a solid (opa == LV_OPA_COVER) background. * Use only if required because it's slower.*/ uint32_t dpi : 10; /** DPI (dot per inch) of the display. Default value is `LV_DPI_DEF`.*/ /** MANDATORY: Write the internal buffer (draw_buf) to the display. 'lv_disp_flush_ready()' has to be * called when finished*/ void (*flush_cb)(struct _lv_disp_drv_t * disp_drv, const lv_area_t * area, lv_color_t * color_p); /** OPTIONAL: Extend the invalidated areas to match with the display drivers requirements * E.g. round `y` to, 8, 16 ..) on a monochrome display*/ void (*rounder_cb)(struct _lv_disp_drv_t * disp_drv, lv_area_t * area); /** OPTIONAL: Set a pixel in a buffer according to the special requirements of the display * Can be used for color format not supported in LittelvGL. E.g. 2 bit -> 4 gray scales * @note Much slower then drawing with supported color formats.*/ void (*set_px_cb)(struct _lv_disp_drv_t * disp_drv, uint8_t * buf, lv_coord_t buf_w, lv_coord_t x, lv_coord_t y, lv_color_t color, lv_opa_t opa); void (*clear_cb)(struct _lv_disp_drv_t * disp_drv, uint8_t * buf, uint32_t size); /** OPTIONAL: Called after every refresh cycle to tell the rendering and flushing time + the * number of flushed pixels*/ void (*monitor_cb)(struct _lv_disp_drv_t * disp_drv, uint32_t time, uint32_t px); /** OPTIONAL: Called periodically while lvgl waits for operation to be completed. * For example flushing or GPU * User can execute very simple tasks here or yield the task*/ void (*wait_cb)(struct _lv_disp_drv_t * disp_drv); /** OPTIONAL: Called when lvgl needs any CPU cache that affects rendering to be cleaned*/ void (*clean_dcache_cb)(struct _lv_disp_drv_t * disp_drv); /** OPTIONAL: called when driver parameters are updated */ void (*drv_update_cb)(struct _lv_disp_drv_t * disp_drv); /** On CHROMA_KEYED images this color will be transparent. * `LV_COLOR_CHROMA_KEY` by default. (lv_conf.h)*/ lv_color_t color_chroma_key; lv_draw_ctx_t * draw_ctx; void (*draw_ctx_init)(struct _lv_disp_drv_t * disp_drv, lv_draw_ctx_t * draw_ctx); void (*draw_ctx_deinit)(struct _lv_disp_drv_t * disp_drv, lv_draw_ctx_t * draw_ctx); size_t draw_ctx_size; #if LV_USE_USER_DATA void * user_data; /**< Custom display driver user data*/ #endif } lv_disp_drv_t;前面的是一些常规的显示设置和显存写回调函数，后面有一个“draw_ctx”字段，这个是一个”绘制语境“结构体，里面包含了最常用几何图形、图片、字符的绘制函数： typedef struct _lv_draw_ctx_t { /** * Pointer to a buffer to draw into */ void * buf; /** * The position and size of `buf` (absolute coordinates) */ lv_area_t * buf_area; /** * The current clip area with absolute coordinates, always the same or smaller than `buf_area` */ const lv_area_t * clip_area; void (*draw_rect)(struct _lv_draw_ctx_t * draw_ctx, const lv_draw_rect_dsc_t * dsc, const lv_area_t * coords); void (*draw_arc)(struct _lv_draw_ctx_t * draw_ctx, const lv_draw_arc_dsc_t * dsc, const lv_point_t * center, uint16_t radius, uint16_t start_angle, uint16_t end_angle); void (*draw_img_decoded)(struct _lv_draw_ctx_t * draw_ctx, const lv_draw_img_dsc_t * dsc, const lv_area_t * coords, const uint8_t * map_p, lv_img_cf_t color_format); lv_res_t (*draw_img)(struct _lv_draw_ctx_t * draw_ctx, const lv_draw_img_dsc_t * draw_dsc, const lv_area_t * coords, const void * src); void (*draw_letter)(struct _lv_draw_ctx_t * draw_ctx, const lv_draw_label_dsc_t * dsc, const lv_point_t * pos_p, uint32_t letter); void (*draw_line)(struct _lv_draw_ctx_t * draw_ctx, const lv_draw_line_dsc_t * dsc, const lv_point_t * point1, const lv_point_t * point2); void (*draw_polygon)(struct _lv_draw_ctx_t * draw_ctx, const lv_draw_rect_dsc_t * draw_dsc, const lv_point_t * points, uint16_t point_cnt); /** * Replace the buffer with a rect without decoration like radius or borders */ void (*draw_bg)(struct _lv_draw_ctx_t * draw_ctx, const lv_draw_rect_dsc_t * draw_dsc, const lv_area_t * coords); /** * Wait until all background operations are finished. (E.g. GPU operations) */ void (*wait_for_finish)(struct _lv_draw_ctx_t * draw_ctx); /** * Copy an area from buffer to an other * @param draw_ctx pointer to a draw context * @param dest_buf copy the buffer into this buffer * @param dest_stride the width of the dest_buf in pixels * @param dest_area the destination area * @param src_buf copy from this buffer * @param src_stride the width of src_buf in pixels * @param src_area the source area. * * @note dest_area and src_area must have the same width and height * but can have different x and y position. * @note dest_area and src_area must be clipped to the real dimensions of the buffers */ void (*buffer_copy)(struct _lv_draw_ctx_t * draw_ctx, void * dest_buf, lv_coord_t dest_stride, const lv_area_t * dest_area, void * src_buf, lv_coord_t src_stride, const lv_area_t * src_area); #if LV_USE_USER_DATA void * user_data; #endif } lv_draw_ctx_t;“draw_ctx”后面还有一个“draw_ctx_init”字段，在"lv_disp_drv_init"函数中，如果没有使用硬件GPU的话，会被默认初始化成“lv_draw_sw_init_ctx”函数，这个函数中会将“draw_ctx”字段中的所有绘制回调函数都初始化成软绘（软件绘制）函数，软绘函数都是使用CPU进行绘制处理，如果有GPU的话，可以使用GPU绘制函数初始化“draw_ctx”。 以“draw_ctx”里的“draw_letter”函数为例，这是字符绘制函数，软绘字符绘制函数为“lv_draw_sw_letter”，在这个函数里面会调用“lv_font_get_glyph_dsc”函数用以获取glyph descriptor（字符描述符），如果获取描述符失败，则会显示一个placeholder（占位符，是一个方框框，如下图），表示这个字符是字库里面没有的字符。否则，就会从字库里面获取字符的点阵数据并绘制。
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