The main driver for receiving touch input on Nerves devices.

So far only tested on Raspberry Pi 3 devices. In other words, it is still early days for this driver. There will probably be changes in the future. Especially regarding multi-touch.

For now, the events coming to a scene via the touch driver look like the same cursor oriented events that come from glfw with a mouse.

In your Nerves applications dependencies include the following line

...
{:scenic_driver_nerves_touch, , "~> 0.9"}
...

You do not need to include it in the "host" mix target deps. There you should be using the glfw driver and that will take care of the touch input for you.

Configure the touch driver the same way you configure other drivers. Add it to the driver list in your ViewPort's config.exs file.

config :sample, :viewport, %{
      size: {800, 480},
      default_scene: {Sample.Scene.Simple, nil},
      drivers: [
        %{
          module: Scenic.Driver.Nerves.Rpi,
        },
        %{
          module: Scenic.Driver.Nerves.Touch,
          opts: [
            device: "FT5406 memory based driver",
            calibration: {{1,0,0},{0,1,0}}
          ],
        }
      ]
    }

This is important

You need to supply the name of the OS driver you are getting the touch information from. You don't need to supply the entire string, but what you supply must be in the actual device name.

When you use the sample scene set up by scenic.new.nerves, it will display the available device names. Otherwise, use the hex package input_event to enumerate them.

Note that some drivers take a short time to come online. (I'm looking at you FT5406). Don't be surprised if touch doesn't work for a second or two after the rest of the UI starts to work. Other drivers initialize themselves faster.

The device name is this part of the configuration

device: "FT5406 memory based driver",

Note: If you're using nerves_system_rpi3 version 1.13.1 or later the device name for the official Raspberry pi 7" touch screen is raspberrypi-ts instead of FT5406 memory based driver

Calibration maps the resolution/coordinates of the touch screen to the coordinates and scale of the display. On the official Raspberry Pi 7" touch screen, then are the same, so the mapping is easy (1.0).

However, with other displays (I have a Dell touchscreen I've tested with), that is not the case and you need to provide a proper mapping. The values are sufficient to support some rotation and out-of-alignment issues in the future, but I haven't written a calibration scene yet to provide those values in an easy/automatic way.

{{ax, bx, dx}, {ay, by dy}}

When a location {x, y} comes in from the touch screen, it is projected by the calibration data via the formula

final_x = x * ax + y * bx + dx
final_y = x * ay + y * by + dy

See Calibration in touch-screen systems for more information.

If the touch panel is not rotate or otherwise out of alignment, then you can supply a simple calibration by providing scale factors for ax and ay.

The calibration is this part of the configuration

calibration: {{1,0,0},{0,1,0}}