zw963
June 12, 2025, 10:55am
1
There are some generate PNG shards. but i don’t know how to make image with text in it.
Hi everyone, I wanted to share my PNG implementation in crystal: GitHub - SleepingInsomniac/png: PNG implementation in Crystal . I started working on it to support another project since I didn’t see an existing project with support for all the bit depths, color types, paletted images etc… It was a pretty fun learning experience, and I’m wondering what others think.
I found some example code in pixie shards works for what i need, but the example code not work on my Arch Linux, check this issue.
Right now, I just want to make a small, simple picture with some numbers on it. It will be used as a simple check when people sign up on my website.
Thanks.
This file has code doing it. If you want I can do a more minimal example.
require "../formatter"
require "compress/gzip"
require "digest/sha1"
require "stumpy_png"
require "stumpy_utils"
module Tartrazine
def self.to_png(text : String, language : String,
theme : String = "default-dark",
line_numbers : Bool = false) : String
buf = IO::Memory.new
Tartrazine::Png.new(
theme: Tartrazine.theme(theme),
line_numbers: line_numbers
).format(text, Tartrazine.lexer(name: language), buf)
buf.to_s
end
class FontFiles
show original
zw963
June 12, 2025, 1:11pm
3
Thanks a lot, will be check later.
I found another working solution, which use crystal-vips.
require "../src/vips"
# Captcha generator
# Reference: https://github.com/libvips/libvips/issues/898
def wobble(image)
# a warp image is a 2D grid containing the new coordinates of each pixel with
# the new x in band 0 and the new y in band 1
#
# you can also use a complex image
#
# start from a low-res XY image and distort it
xy = Vips::Image.xyz(image.width // 20, image.height // 20)
x_distort = Vips::Image.gaussnoise(xy.width, xy.height)
y_distort = Vips::Image.gaussnoise(xy.width, xy.height)
xy += (x_distort.bandjoin(y_distort) / 150)
xy = xy.resize(20)
xy *= 20
show original
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zw963
June 12, 2025, 5:20pm
4
Create a captcha shard use naqvis/crystal-vips
Crystal library that generates image CAPTCHAs.
All credits goes to the example code in crystal-vips by @naqvis
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I don’t think this will be viable for a text-based captcha implementation but for the general case where the images looks relatively the same you could get away with just creating SVGs and then converting to a PNG.
The clock captchas that Invidious uses during registrations are generated this way by manipulating SVG attributes on each picture:
clock_svg = <<-END_SVG
<svg viewBox="0 0 100 100" width="200px" height="200px">
<circle cx="50" cy="50" r="45" fill="#eee" stroke="black" stroke-width="2"></circle>
<text x="69" y="20.091" text-anchor="middle" fill="black" font-family="Arial" font-size="10px"> 1</text>
<text x="82.909" y="34" text-anchor="middle" fill="black" font-family="Arial" font-size="10px"> 2</text>
<text x="88" y="53" text-anchor="middle" fill="black" font-family="Arial" font-size="10px"> 3</text>
<text x="82.909" y="72" text-anchor="middle" fill="black" font-family="Arial" font-size="10px"> 4</text>
<text x="69" y="85.909" text-anchor="middle" fill="black" font-family="Arial" font-size="10px"> 5</text>
<text x="50" y="91" text-anchor="middle" fill="black" font-family="Arial" font-size="10px"> 6</text>
<text x="31" y="85.909" text-anchor="middle" fill="black" font-family="Arial" font-size="10px"> 7</text>
<text x="17.091" y="72" text-anchor="middle" fill="black" font-family="Arial" font-size="10px"> 8</text>
<text x="12" y="53" text-anchor="middle" fill="black" font-family="Arial" font-size="10px"> 9</text>
<text x="17.091" y="34" text-anchor="middle" fill="black" font-family="Arial" font-size="10px">10</text>
<text x="31" y="20.091" text-anchor="middle" fill="black" font-family="Arial" font-size="10px">11</text>
<text x="50" y="15" text-anchor="middle" fill="black" font-family="Arial" font-size="10px">12</text>
<circle cx="50" cy="50" r="3" fill="black"></circle>
<line id="second" transform="rotate(#{second_angle}, 50, 50)" x1="50" y1="50" x2="50" y2="12" fill="black" stroke="black" stroke-width="1"></line>
<line id="minute" transform="rotate(#{minute_angle}, 50, 50)" x1="50" y1="50" x2="50" y2="16" fill="black" stroke="black" stroke-width="2"></line>
show original
3 Likes
zw963
June 15, 2025, 6:26am
6
There is a sister shard, name simple_captcha
All credits goes to @Sunrise
The different is:
SimpleCaptcha has no external dependencies other than Crystal，so, you can
this shard captcha code only support number.
These two libraries should be interchangeable without the need to change you code.
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