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-- A simple demonstration of creating a 'user font' in Lua. The new user
-- font feature in Cairo 1.8 allows you to define a font's metrics and
-- glyph images by providing callback functions, which Lua calls as needed.
-- The idea is that you can provide Cairo with access to fonts in unusual
-- formats it wouldn't normally understand, or create special effects.
--
-- Note that for now at least user fonts can't contain colour information,
-- only shapes drawn with the Cairo context provided to the rendering
-- callback. You're not allowed to use the 'set_source' methods on it.
-- Also, there seem to be some problems with generating PDF output with
-- user fonts.
--
-- This example has callbacks which make a font based purely on the Unicode
-- codepoint numbers used for characters. Each character is drawn as a box
-- with some diamonds in, which indicate which bits are set in the codepoint
-- number. I can't think of any practical use for this, but I wanted
-- something simple to draw which wouldn't require a bunch of ancillary
-- font data.
--
-- I'm relying on the default glyph index mapping, which is that the glyph
-- index numbers are exactly the same as the Unicode codepoints of the
-- characters. You can do more interesting things by providing other
-- callback functions, but for this example we just need the rendering one.
-- The rendering callback also provides the metrics for each character.
-- We actually leave them as their defaults, except for the width of the
-- glyphs, which can be wider for larger numbered characters (because we
-- display them with several columns of bits).
local Cairo = require "oocairo"
if not Cairo.user_font_face_create then
error("User font example requires module built with Cairo 1.8", 0)
end
local BIT_WIDTH, BIT_HEIGHT, CHAR_GAP = 0.2, 1 / 8, 0.1
local function make_bit_font ()
local function render_glyph (font, glyph, cr, extents)
if glyph == 32 then return end -- space, just default advance
-- Draw a diamond shape for each bit which is set within the codepoint
-- number, with eight bits per column.
local n = glyph
local x = 0
while n ~= 0 do
local byte = n % 0x100
n = (n - byte) / 0x100
for i = 0, 7 do
local bit = byte % 2
byte = (byte - bit) / 2
if bit ~= 0 then
cr:move_to(x, (i + 0.5) * BIT_HEIGHT)
cr:rel_line_to(BIT_WIDTH / 2, BIT_HEIGHT / 2)
cr:rel_line_to(BIT_WIDTH / 2, -BIT_HEIGHT / 2)
cr:rel_line_to(-BIT_WIDTH / 2, -BIT_HEIGHT / 2)
cr:close_path()
cr:fill()
end
end
x = x + BIT_WIDTH
end
-- Box round edge, 1 pixel wide and aligned on a pixel in device
-- coordinates (so that it's sharp, and as thin as possible).
local xpix, ypix = cr:device_to_user_distance(1, 1)
cr:rectangle(xpix / 2, ypix / 2, x - xpix, 1 - ypix)
cr:set_line_width(xpix)
cr:stroke()
extents.x_advance = x + CHAR_GAP
end
return Cairo.user_font_face_create({ render_glyph = render_glyph })
end
local surface = Cairo.image_surface_create("rgb24", 440, 230)
local cr = Cairo.context_create(surface)
-- White background.
cr:set_source_rgb(1, 1, 1)
cr:paint()
cr:set_font_face(make_bit_font())
cr:set_font_size(50)
-- Draw lines of text, each in a different colour.
local x, y = 20, 20
for _, info in ipairs{
{ "The quick brown fox,", { .5, 0, 0 } },
{ "jumped lazy dog…", { 0, .5, 0 } },
-- These characters will have three columns of bits because they have
-- large Unicode codepoint numbers. They're actually a random selection
-- of cuneiform characters.
{ "𒀽𒍬𒍭𒍅𒌡𒌤", { 0, 0, .5 } },
} do
local line, color = unpack(info)
cr:move_to(x, y)
cr:set_source_rgb(unpack(color))
cr:show_text(line)
y = y + 70
end
surface:write_to_png("text-userfont.png")
-- vi:ts=4 sw=4 expandtab
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