acid-drop

- Hacking the planet from a LilyGo T-Deck using custom firmware
git clone git://git.acid.vegas/acid-drop.git
canvas.md (4969B)
      1 ```eval_rst
      2 .. include:: /header.rst
      3 :github_url: |github_link_base|/widgets/core/canvas.md
      4 ```
      5 # Canvas (lv_canvas)
      6 
      7 
      8 ## Overview
      9 
     10 A Canvas inherits from [Image](/widgets/core/img) where the user can draw anything.
     11 Rectangles, texts, images, lines, arcs can be drawn here using lvgl's drawing engine.
     12 Additionally "effects" can be applied, such as rotation, zoom and blur.
     13 
     14 
     15 ## Parts and Styles
     16 `LV_PART_MAIN` Uses the typical rectangle style properties and image style properties.
     17 
     18 ## Usage
     19 
     20 ### Buffer
     21 The Canvas needs a buffer in which stores the drawn image.
     22 To assign a buffer to a Canvas, use `lv_canvas_set_buffer(canvas, buffer, width, height, LV_IMG_CF_...)`.
     23 Where  `buffer` is a static buffer (not just a local variable) to hold the image of the canvas.
     24 For example,
     25 `static lv_color_t buffer[LV_CANVAS_BUF_SIZE_TRUE_COLOR(width, height)]`.
     26 `LV_CANVAS_BUF_SIZE_...` macros help to determine the size of the buffer with different color formats.
     27 
     28 The canvas supports all the built-in color formats like `LV_IMG_CF_TRUE_COLOR` or `LV_IMG_CF_INDEXED_2BIT`.
     29 See the full list in the [Color formats](/overview/image.html#color-formats) section.
     30 
     31 ### Indexed colors
     32 For `LV_IMG_CF_INDEXED_1/2/4/8` color formats a palette needs to be
     33 initialized with  `lv_canvas_set_palette(canvas, 3, LV_COLOR_RED)`. It sets pixels with *index=3* to red.
     34 
     35 ### Drawing
     36 To set a pixel's color on the canvas, use `lv_canvas_set_px_color(canvas, x, y, LV_COLOR_RED)`.
     37 With `LV_IMG_CF_INDEXED_...`  the index of the color needs to be passed as color.
     38 E.g. `lv_color_t c; c.full = 3;`
     39 
     40 To set a pixel's opacity with `LV_IMG_CF_TRUE_COLOR_ALPHA` or `LV_IMG_CF_ALPHA_...` format on the canvas, use `lv_canvas_set_px_opa(canvas, x, y, opa)`.
     41 
     42 
     43 `lv_canvas_fill_bg(canvas, LV_COLOR_BLUE, LV_OPA_50)` fills the whole canvas to blue with 50% opacity. Note that if the current color format doesn't support colors (e.g. `LV_IMG_CF_ALPHA_2BIT`) the color will be ignored.
     44 Similarly, if opacity is not supported (e.g. `LV_IMG_CF_TRUE_COLOR`) it will be ignored.
     45 
     46 An array of pixels can be copied to the canvas with `lv_canvas_copy_buf(canvas, buffer_to_copy, x, y, width, height)`.
     47 The color format of the buffer and the canvas need to match.
     48 
     49 To draw something to the canvas use
     50 - `lv_canvas_draw_rect(canvas, x, y, width, heigth, &draw_dsc)`
     51 - `lv_canvas_draw_text(canvas, x, y, max_width, &draw_dsc, txt)`
     52 - `lv_canvas_draw_img(canvas, x, y, &img_src, &draw_dsc)`
     53 - `lv_canvas_draw_line(canvas, point_array, point_cnt, &draw_dsc)`
     54 - `lv_canvas_draw_polygon(canvas, points_array, point_cnt, &draw_dsc)`
     55 - `lv_canvas_draw_arc(canvas, x, y, radius, start_angle, end_angle, &draw_dsc)`
     56 
     57 `draw_dsc` is a `lv_draw_rect/label/img/line/arc_dsc_t` variable which should be first initialized with one of `lv_draw_rect/label/img/line/arc_dsc_init()` and then modified with the desired colors and other values.
     58 
     59 The draw function can draw to any color format. For example, it's possible to draw a text to an `LV_IMG_VF_ALPHA_8BIT` canvas and use the result image as a [draw mask](/overview/drawing) later.
     60 
     61 ### Transformations
     62 `lv_canvas_transform()` can be used to rotate and/or scale the image of an image and store the result on the canvas.
     63 The function needs the following parameters:
     64 - `canvas` pointer to a canvas object to store the result of the transformation.
     65 - `img pointer` to an image descriptor to transform. Can be the image descriptor of another canvas too (`lv_canvas_get_img()`).
     66 - `angle` the angle of rotation (0..3600), 0.1 deg resolution
     67 - `zoom` zoom factor (256: no zoom, 512: double size, 128: half size);
     68 - `offset_x` offset X to tell where to put the result data on destination canvas
     69 - `offset_y` offset X to tell where to put the result data on destination canvas
     70 - `pivot_x` pivot X of rotation. Relative to the source canvas. Set to `source width / 2` to rotate around the center
     71 - `pivot_y` pivot Y of rotation. Relative to the source canvas. Set to `source height / 2` to rotate around the center
     72 - `antialias` true: apply anti-aliasing during the transformation. Looks better but slower.
     73 
     74 Note that a canvas can't be rotated on itself.  You need a source and destination canvas or image.
     75 
     76 ### Blur
     77 A given area of the canvas can be blurred horizontally with `lv_canvas_blur_hor(canvas, &area, r)` or vertically with `lv_canvas_blur_ver(canvas, &area, r)`.
     78 `r` is the radius of the blur (greater value means more intensive burring). `area` is the area where the blur should be applied (interpreted relative to the canvas).
     79 
     80 ## Events
     81 No special events are sent by canvas objects.
     82 The same events are sent as for the
     83 
     84 See the events of the [Images](/widgets/core/img) too.
     85 
     86 Learn more about [Events](/overview/event).
     87 
     88 ## Keys
     89 No *Keys* are processed by the object type.
     90 
     91 Learn more about [Keys](/overview/indev).
     92 
     93 ## Example
     94 ```eval_rst
     95 
     96 .. include:: ../../../examples/widgets/canvas/index.rst
     97 
     98 ```
     99 
    100 ## API
    101 
    102 ```eval_rst
    103 
    104 .. doxygenfile:: lv_canvas.h
    105   :project: lvgl
    106 
    107 ```