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-- Example of how to use 'push_group' and 'pop_group_to_source' to composite
-- a bunch of drawing commands onto a background with a single level of
-- alpha blending, and also demonstrate the difference between the
-- 'get_target' and 'get_group_target' methods.
local Cairo = require "oocairo"
local PI = 2*math.asin(1)
local IMG_WD, IMG_HT = 450, 450
local surface = Cairo.image_surface_create("rgb24", IMG_WD, IMG_HT)
local cr = Cairo.context_create(surface)
-- White background.
cr:set_source_rgb(1, 1, 1)
cr:paint()
-- Black cross to show through the translucent circles.
cr:set_source_rgb(0, 0, 0)
cr:move_to(0, 0)
cr:line_to(IMG_WD, IMG_HT)
cr:move_to(0, IMG_HT)
cr:line_to(IMG_WD, 0)
cr:set_line_width(20)
cr:stroke()
cr:push_group()
for _, v in ipairs{ {200,1,0,0}, {150,0,1,0}, {100,0,0,1}, {50,0,0,0} } do
local radius, r, g, b = unpack(v)
cr:arc(IMG_WD/2, IMG_HT/2, radius, 0, 2*PI)
cr:set_source_rgb(r, g, b)
cr:fill()
end
local function draw_text_on_surface (surface, y, text)
local tmpcr = Cairo.context_create(surface)
tmpcr:move_to(20, y)
tmpcr:set_source_rgb(0, 0, 0)
tmpcr:set_font_size(40)
tmpcr:show_text(text)
end
draw_text_on_surface(cr:get_target(), IMG_HT / 2 - 70, "get_target")
draw_text_on_surface(cr:get_group_target(), IMG_HT / 2 + 80, "get_group_target")
cr:pop_group_to_source()
cr:paint_with_alpha(0.5)
surface:write_to_png("groups.png")
-- vi:ts=4 sw=4 expandtab
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