latex as an ad blocker

content/tips/latex-adblock.md

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+---
+Title: Block ads with LaTeX
+Date: 2019-04-23 08:00
+Author: Fabrice
+Category: tips
+Tags: LaTeX, inkscape, ads
+Slug: latex-ad-block
+Header_Cover: images/cover_velov.jpg
+---
+
+I'm quite annoyed with ads. As of many, I'm using an adblocker on my computer, but there is one kind of ads that annoys me the most: ads on printable ticket. Not only it poisons our eyes, but it consumes ink to print it.
+
+I'm aware that we can just open the QR/barcode on your smartphone, but still, isn't it better if we can get rid of the ad directly?
+
+To do this, I tried the most obvious solution: open it with inkscape, and remove the image.
+However, this approach has a serious drawback, it breaks the fonts, and some of them (such as Air France's “Excellence in Motion” font) are proprietary and cannot be found easily/legally for free.
+
+But inkscape can still be of use in order to remove those ads.
+Indeed, it allows finding the coordinates and the dimensions of those ads as illustrated in the following (click to zoom):
+[![Inkscape ad dimensions](/examples/inkscape-adblock.png)](/examples/inkscape-adblock.png)
+
+**Explanations:** After opening your pdf file, start by selecting the ad (<span style="color:#8b0074">purple</span>), you may have to ungroup elements (`ctrl+shift+g`), then set the dimensions in cm or your favourite length unit (<span style="color:#0000ff">blue</span>) and finally note the dimensions of the ad (<span style="color:#ff0000">red</span>).
+
+Then we just use LaTeX to add a white (or any background color, I let you devise it by yourself, you can use RGB codes with [xcolor](https://www.ctan.org/pkg/xcolor)) rectangle in front of the ad.
+I already used the [wallpaper](https://www.ctan.org/pkg/wallpaper) package in [another post](/latex-letterhead.html), but it has some limitations: it doesn't allow us to import multiple pages (such as a round-trip ticket), and tikz doesn't interact well with the induced page geometry.
+
+Thus, I used this [answer on stackexchange](https://tex.stackexchange.com/questions/12838/can-i-add-tikzpictures-to-pages-included-with-pdfpages).
+To put it short, we use the package [pdfpages](https://ctan.org/pkg/pdfpages) with its options `pages={-}` to include every page, and the option `pagecommand` to include the rectangle overlay with the right dimensions `X`, `Y`, `L`, `H`.
+That gives us the following `.tex`.
+
+```tex
+\documentclass[a4paper]{article}
+% Tikz with pdfpages
+\usepackage{tikz}
+\usetikzlibrary{calc}
+\usepackage{pdfpages}
+% avoid page numbering
+\pagestyle{empty}
+\begin{document}
+\includepdf[pages={-},% include all pages
+  pagecommand={% is called at the beginning of each inclusion
+    \begin{tikzpicture}[remember picture,overlay]
+      \draw[color=white,fill=white] ($(current page.north west) +%
+         (X, -Y)$) rectangle ++ (L, -H);%
+    \end{tikzpicture}%
+}]%
+{af.pdf}
+\end{document}
+```
+
+**Remark:** You may have noticed the minus sign in front of `Y` and `H`. This is because tikz computes coordinates from bottom left of the page, while inkscape (and gimp) starts at top left (and the frame is oriented accordingly).
+
+Some examples of dimensions to copy-paste (mostly for myself):
+
+* Rhônexpress:
+```tex
+… + (1.5cm, -14.65cm)$) rectangle ++ (18cm, -9cm);
+```
+* Air France/KLM foldable tickets.
+```tex
+… + (11cm, -18cm)$) rectangle ++ (9cm, -9cm);
+```
+You may have noticed that the dimensions are larger than in the above picture, this is because Air France sometime uses square ads.  
+However, if you plan to use your smartphone, these companies also attach an ad-free `png` with minimal information.
+
+
+As I don't buy a plane ticket every day, I didn't feel the need to script it, and I don't have enough examples to make an interesting enough database of ad locations. However, if you are interested in it, feel free to send me dimensions and type of pdf (for instance a brand name) by email at <img style="height:2em" src="/images/mel.png" alt="courriel"/>.
+
+<center>
+![xkcd 1319 Randall Munroe](https://imgs.xkcd.com/comics/automation.png)]  
+[XKCD #1319](https://xkcd.com/1319/) by Randall Munroe.
+</center>