Nice sparklines for ESP8266, ESP32, Arduino

Sparklines are small, high resolution graphics embedded in a context of words, numbers or images". Edward Tufte describes sparklines as "data-intense, design-simple, word-sized graphics".

Read more about Sparklines here.

Help wanted – I appreciate PRs with

• examples for other architectures
• examples for different display libraries

This library is very simple, it

• holds a buffer of any numeric data type of speficied size
• renders sparklines using a passed-in function to draw lines
• uses the line drawing function of your preferred graphics library (u8g2, Adafruit, ...)

Click picture to watch video (35sec) on YouTube	Example App: Geiger Counter

Create Sparkline with a buffer for 25 items of uint16_t and pass in your existing line drawing function. I use u8g2's drawLine():

SparkLine<uint16_t> MySparkLine(25, [&](const uint16_t x0, const uint16_t y0, const uint16_t x1, const uint16_t y1) { 
  u8g2.drawLine(x0, y0, x1, y1);
});

This example uses a lambda expression (aka. 'closure' or anonymous / unnamed function: [] ( <parameters> ) { <code> }) to match the function signature of u8g2's drawLine(). For the AdafruitGFX library, change to tft.drawLine(x0, y0, x1, y1, myColor);, if myColor holds your line color in the current function scope. The ampersand [&] captures scope, so your outside variables are available inside { }.

Next, add data regularly, e.g. every minute upon sensor read, or analogRead(), etc. The data will be automatically scaled and automatically rotated (FIFO), once the buffer exceeds the specified number of items.

MySparkLine.add(42);

Then, periodically display sparkline at 0x10, 50 pixel wide, 20 pixel high, e.g. from loop() like so:

static esp8266::polledTimeout::periodicMs periodicSecond(1000);

if (periodicSecond) {
  MySparkLine.draw(0, 10, 50, 20);
}

This library depends on FixedPointsArduino. It will be automatically installed via PlatformIO.

To remove this dependency, redefine num_t to float or double and remove all occurences of .getInteger() in SparkLine.h.

MIT License

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