1CANVAS_WIDTH   = 50
2CANVAS_HEIGHT  = 50
3LV_COLOR_CHROMA_KEY = lv.color_hex(0x00ff00)
4
5def LV_IMG_BUF_SIZE_ALPHA_1BIT(w, h):
6    return int(((w / 8) + 1) * h)
7
8def LV_IMG_BUF_SIZE_INDEXED_1BIT(w, h):
9    return LV_IMG_BUF_SIZE_ALPHA_1BIT(w, h) + 4 * 2
10
11def LV_CANVAS_BUF_SIZE_INDEXED_1BIT(w, h):
12    return LV_IMG_BUF_SIZE_INDEXED_1BIT(w, h)
13
14#
15# Create a transparent canvas with Chroma keying and indexed color format (palette).
16#
17
18# Create a button to better see the transparency
19btn=lv.btn(lv.scr_act())
20
21# Create a buffer for the canvas
22cbuf= bytearray(LV_CANVAS_BUF_SIZE_INDEXED_1BIT(CANVAS_WIDTH, CANVAS_HEIGHT))
23
24# Create a canvas and initialize its palette
25canvas = lv.canvas(lv.scr_act())
26canvas.set_buffer(cbuf, CANVAS_WIDTH, CANVAS_HEIGHT, lv.img.CF.INDEXED_1BIT)
27canvas.set_palette(0, LV_COLOR_CHROMA_KEY)
28canvas.set_palette(1, lv.palette_main(lv.PALETTE.RED))
29
30# Create colors with the indices of the palette
31c0 = lv.color_t()
32c1 = lv.color_t()
33
34c0.full = 0
35c1.full = 1
36
37# Red background (There is no dedicated alpha channel in indexed images so LV_OPA_COVER is ignored)
38canvas.fill_bg(c1, lv.OPA.COVER)
39
40# Create hole on the canvas
41for y in range(10,30):
42    for x in range(5,20):
43        canvas.set_px(x, y, c0)
44