As promised in last week's episode, we will discover today another great feature of the hotspot component, in conjunction with the slider component to learn more about Nextion's RGB565 color encoding scheme. We'll use all that to build a tiny hue control with a 3.2" Standard HMI, as usual.

After we had looked into some basics of touch GUI technology and NEXTION's advantages over proprietary solutions, last week, and we made acquaintance with the most elementary and simple hotspot component, it's time to move on. Most other components inherit from the hotspot since they have the same attributes (plus more specific ones in addition) and they have identical Touch Press and Touch Release events and the corresponding Send Component ID functionality. Out of that, the hotspot gives us another huge advantage for optimizing our Nextion code, but we will look into that in a further episode.

The Sunday Blog: Understanding and Customizing HMI components Part 1: Introduction From today on, for the next

Today, after 5 weeks of blogging about our beloved Nextion HMIs doing advanced mathematics, you have learnt about doing calculations with binary fractional numbers, drawing curves and patterns, iterating through sine and cosine functions, thus creating circles, ellipses, and finally complex Lissajous patterns while combining two rotary movements, represented by two sin/cos pairs. More isn't needed to move a visual step further and to transform your Nextion HMI into a Spirograph, only using the Nextion programming language! I'll give you more details below.

In the last episode (Part 4: Trigonometry), we have learned how to quickly and precisely iterate through a full period of sin/cos values, which allowed us to draw either circles having identical radii in x and y direction, or ellipses having different x and y radii. It's time to move on! The French physicist Jules Antoine Lissajous wondered during the 19th century how a geometric figure would look like if one didn't vary the radii in x and y direction as we did when drawing the ellipses, but if one had moving the circular line with different speeds or frequencies, depending on the direction. Mr Lissajous used a complex setting with two tuning forks (set on different tone heights) with a small mirror attached to each, one deflecting a light beam vertically, and the other horizontally. That's how he discovered very beautiful patterns which where later called Lissajous curves.

Today, let's have a look onto trigonometry: While it remains complicated to approximate arbitrary sine and cosine values on an integer based MCU like the ARM Cortex M0 inside our NEXTION HMI with reasonable precision, methods exist which allow to step from one already known value to the next under the condition that the step is small. As most of you know, the gradient of a function y = f(x) in a specific point (x0,y0) is given by the value of its derivative y' = f'(x) in that point. This allows us to approximate a neighbored point located at x0 + d by f(x0 + d) = f(x0) + d * f'(x0). So we can recursively move from one point to the next. This approach is the more precise the more we make the step d small. But smaller d values require naturally more iterations which slows down the curve drawing. You will have to find the best compromise between speed and precision.