Users who can generate screens themselves, can make use of our Alias plugin.
As the name indicates, this plugin simply passes along your own (hosted) image to your TRMNL device. This may sound similar to our Image Display plugin, but with one key difference: your device downloads the image straight from your URL, so the image never passes through TRMNL's servers.
How it works
TRMNL expects image content to be accessible over the internet / home-network. You then enter the URL of this image into the TRMNL web application in plain text.
The diagram below shows how the Plain Text type works (top) and how the planned Encrypted type would work (bottom). Encrypted is not available yet.
Getting started
To set up an Alias plugin, first provide the absolute URL of your image.
Make sure the image is 1 bit bitmap(bmp3), 1-bit PNG, or 2-bit PNG (OG model, firmware v1.6.x or higher), 800x480 pixels (OG) or 1872 × 1404 pixels (X). See here for a hint on generating this format with ImageMagick.
Type - Plain Text
When your TRMNL device requests content from your Alias plugin instance, TRMNL will respond with the data you provided in the TRMNL web application. For example, https://yourwebserver.com/image1.bmp as per the screenshot above.
Type - Encrypted
The Type menu lists Encrypted (Coming Soon). It is not available yet: TRMNL sends your URL to your device as you entered it, whichever type you pick. Use Plain Text.
Putting it all together
The Alias plugin lets you generate and show your own content without sending the image through the TRMNL servers, while still leveraging the convenience and power of the TRMNL web application.
Troubleshooting
Request origins
Whatever the exact URL is that can be reached by your local network, use that in the URL field. Your device downloads the image itself, so use an address it can reach on your WiFi network. If you're running a server on a computer at 192.168.1.50, port 4567, provide the full URL: http://192.168.1.50:4567/my/image.png. Do not use localhost: on the device, that points at the device itself. It does not have to be https.
Image metadata
Most issues with this plugin are due to the image formatting not matching our specifications exactly. For example, the OG TRMNL device model expects 800x480 pixel images, not 1600x960 or some other equivalent ratio.
Image response headers
There have been reports that your image's endpoint must respond with a content-length header; the value should be an integer. This is a requirement we are actively investigating and intend to remove. If you are generating images on the fly, you may not have this value by default because the content is still streaming. In this case, use a dummy value.
Caching
At the bottom of your Alias plugin settings, there is a section called Enable cache?:
If set to no, your device will always re-draw the image URL, even if its filename matches the last rendered filename (e.g., the image is rewritten at the source using the same filename).
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