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-- Draw a rectangle with different transformations to rotate and scale it.
-- It also has a translation applied, although that's always the same.
-- This also uses 'save' and 'restore' to push and pop the transformation
-- matrix, so that the translation doesn't have to be applied to a fresh
-- identity matrix each time round.
local Cairo = require "oocairo"
local PI = 2*math.asin(1)
local BOX_SZ, MARGIN = 300, 10
local IMG_CENTER = math.sqrt(2 * (BOX_SZ / 2) ^ 2) + MARGIN
local IMG_SZ = 2 * IMG_CENTER
local PARAMS = {
{ scale = 1, num_boxes = 7, color = { 0, 0, 0, 0.2 } },
{ scale = 0.55, num_boxes = 5, color = { 1, 0.3, 0.3, 0.3 } },
{ scale = 0.25, num_boxes = 3, color = { 0, 0, 0.8, 0.3 } },
}
local surface = Cairo.image_surface_create("rgb24", IMG_SZ, IMG_SZ)
local cr = Cairo.context_create(surface)
-- White background.
cr:set_source_rgb(1, 1, 1)
cr:paint()
cr:translate(IMG_CENTER, IMG_CENTER)
for _, param in ipairs(PARAMS) do
cr:save()
cr:set_source_rgba(unpack(param.color))
cr:scale(param.scale, param.scale)
for _ = 1, param.num_boxes do
cr:rotate(2 * PI / param.num_boxes)
cr:rectangle(-BOX_SZ / 2, -BOX_SZ / 2, BOX_SZ, BOX_SZ)
cr:fill()
end
cr:restore()
end
surface:write_to_png("transform.png")
-- vi:ts=4 sw=4 expandtab
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