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@efatsi /image_pdf_helper.rb Secret
Last active Nov 26, 2018

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module ImagePdfHelper
def image_or_pdf_tag(attachment, width:, height: nil, with_link: false, mime_type: nil)
height ||= width
# fetch mime_type of attachment is one isn't passed in as an argument
mime_type ||= attachment.mime_type
output = if mime_type == "application/pdf"
render_pdf(attachment, width, height)
else
image_tag attachment.thumb("#{width}x#{height}").url
end
if with_link
link_to(attachment.url, target: :_blank) do
output
end
else
output
end
end
def render_pdf(attachment, width, height)
load_pdf_js
uid = SecureRandom.hex(20)
content_tag(:div, content_tag(:span, "", id: uid)).tap do
build_canvas_on_div(uid, attachment, width)
end
end
def load_pdf_js
return if @loaded_pdf_js
content_for(:after_scripts) do
tag.script src: "//npmcdn.com/pdfjs-dist/build/pdf.js"
end
@loaded_pdf_js = true
end
def build_canvas_on_div(uid, attachment, width)
# assumes you have <%= content_for(:after_scripts) %> in your application layout
content_for(:after_scripts) do
script = <<-JS
<script>
var previewDiv#{uid} = document.getElementById("#{uid}")
pdfjsLib.getDocument("#{attachment.url}").then(function (doc) {
doc.getPage(1).then(function(page) {
var vp = page.getViewport(1)
var canvas = document.createElement("canvas")
canvas.width = #{width}
canvas.height = #{width} * (vp.height / vp.width)
var scale = Math.min(canvas.width / vp.width, canvas.height / vp.height)
return page.render({
canvasContext: canvas.getContext("2d"),
viewport: page.getViewport(scale)
}).then(function () {
previewDiv#{uid}.appendChild(canvas)
})
})
})
</script>
JS
script.html_safe
end
end
end
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