PineTime Custom Watchface Tutorial

PineTime Custom Watchface Tutorial

This is a tutorial to help new users create custom watchfaces based on the InfiniTime Firmware for Pinetime made by user JF002, thanks to him for its development...

We will explain some of the things we went through while creating some custom Watchfaces, so consider this as a log of experiments of sorts..

So stay tuned to it as it will be dynamically updated...

What you need to start

The entire building process will be done by GitHub, so all you need is a device which can give you a Github Web Client, a PC or tablet to give you enough screen space to review your code and a steady internet connection.

Since the compiling and file management is done by Github online, you have nothing else to worry about other than working with the files that display the watch face.

So with those things settled, let's start with the basics of a watchface.

Please remember that this is a wiki, so you can make an account and help us improve this page.

Please make sure not to unilaterally remove info though, but offer an alternative. If it is indeed a better way, in time your alternative will grow into the main text, and the latter info will be pruned.

Overview

The Firmware (also called InfiniTime) we will be working with is made with a programming language named C++:[1]

Basic knowledge of C/C++ is required to to understand the advanced watch faces as that requires more complex code, but you can still do a some cool things without much knowledge of C++ programming, just some small edits to existing programs.

InfiniTime uses the LVGL:[2] graphics library to provide users with a simple and clean UI without overpowering the Nordic nRF52832:[3] microcontroller which is the brain of the watch.

To get the watchface to work there are these basic steps. We will go over each step separately, so don't be daunted, all will become clear soon.

For now we will, modify the the existing watchface, change the positioning of the text labels, add an icon to an existing watchface, and later on we will do a full watchface.

The main file we need to focus on is the clock.cpp file, it is what contains most of the data attributed to what we see on the watchface, including The time/day characters, the battery and bluetooth icons, and also pedometer count...

so everything we will be doing in the basic modifications is purely messing with this single file.

Labels

What are labels?

Labels are considered as "elemental" parts that make up a screen's Text-based UI by the LVGL library... Each label is also considered as an "object" or "obj" and can be manipulated, by changing the data attributed with the "obj", for example, position, internal data like the strings/text etc. when can change what the label shows and where it shows it...

Modifying label data

let's observe something small like the word "BPM" near the bottom of the watch face...

If we take a look at the source file of the watchface, (a.k.a the clock.cpp file) we can observe that these particular lines are what attributes to the word "BPM being displayed...

heartbeatBpm = lv_label_create(lv_scr_act(), NULL);
lv_label_set_text(heartbeatBpm, "BPM");

we can modify the text inside the quotes and replace the word 'BPM' between those quotes to something like 'LOVE' and the result after compiling the firmware again with the changes and flashing it to the watch would be that the text changes on the watch face and displays 'LOVE' inplace of 'BPM'...

If this happened correctly, then you have successfully made a custom new watchface! Now we can do something a bit more complex...

Now take for in instance the days of the week that we have on the bottom line with the date...

they are stored a "C array" which is basically multiple words separated by commas.. the date is in a format of <day of the week> <day> <Month> <year>

which in the source file is expressed as,

sprintf(dateStr, "%s %d %s %d", DayOfWeekToString(dayOfWeek), day, MonthToString(month), year);
lv_label_set_text(label_date, dateStr);

here,

%s %d %s %d 

stores the print format of the variables, and

DayOfWeekToString(dayOfWeek), day, MonthToString(month), year  

are the variables themselves...

Now, if the date was a saturday 11/7/2020, you can observe that the date looks like

SATURDAY 11 JUL 2020

as seen in the above image (the one where we changed BPM to LOVE)

by modifying the format of the variables, we can change how those words are arranged, and add some extra characters if we like...

(there is a catch to the list of characters you can use however, but it will be discussed later...)

For example,

We modifying the format by adding a comma... "," in between the second "%s" and "%d" like this,

"%s %d %s, %d"

and changing that in the line...

sprintf(dateStr, "%s %d %s, %d", DayOfWeekToString(dayOfWeek), day, MonthToString(month), year);

we can make the date become...

SATURDAY 11 JUL, 2020

which means we now were able to modify how the text got display to make it a bit more nice...

but if you haven't noticed, the line containing the date is already full, meaning we will get some problems while displaying the date and causing it to wrap around, making a single character go to the next line and look more like,

SATURDAY 11 JUL, 202
0

so why don't we shorten the characters present in the date from being "SATURDAY" to simply just "sat." (It will have the small period at the end, and is only 3 characters long) I will also convert the months of the year from Capital to small letters...

for that look into the part where the days of the week of are stored as text, and also while looking at it, we can solve another question, why was their two variables in the date format that looked like, DayOfWeekToString(dayOfWeek), and MonthToString(month) ?

It is because the system gives the date/ time as numbers (Monday-1, Tuesday-2 Wednesday-3 for the days, and 1-January, 2-February, 3-March ), and so a function along with a C array is used to assign these numbers to Days/Months in text form as it is easier to read...

this is the Array containing the day of the week, (as text)

char const *Clock::DaysString[] = {
       "",
       "MONDAY",
       "TUESDAY",
       "WEDNESDAY",
       "THURSDAY",
       "FRIDAY",
       "SATURDAY",
       "SUNDAY"
};

and this Array stores the months of the year, (as text)

char const *Clock::MonthsString[] = {
       "",
       "JAN",
       "FEB",
       "MAR",
       "APR",
       "MAY",
       "JUN",
       "JUL",
       "AUG",
       "SEP",
       "OCT",
       "NOV",
       "DEC"
};

here we can see that the days are stored in a full format as "SUNDAY", "MONDAY", "TUESDAY" etc. we can change all of them to a shorter format like "sun.", "mon.", "tue.", to make it short and nice... while doing so, we can even make the months use small letters as said before..

so the source file (clock.cpp) becomes,

(for the days of the week)

char const *Clock::DaysString[] = {
       "",
       "mon.",
       "tue.",
       "wed.",
       "thu.",
       "fri.",
       "sat.",
       "sun."
};

and

(for the months of the year)

char const *Clock::MonthsString[] = {
       "",
       "jan",
       "feb",
       "mar",
       "apr",
       "may",
       "jun",
       "jul",
       "aug",
       "sep",
       "oct",
       "nov",
       "dec"
};

which means now our original date, saturday 11/7/2020 will become...

sat. 11 jul, 2020

you now know how to change the data present in a label object, and the format of it..,

Here is a fun idea you can try: you can even replace the days with whatever thing that tells you (or) reminds you the day of the week (like the food served in the cafe, Monday/taco, Tuesday/burger, Wednesday/pasta etc.)

NOTE: when making the custom array, don't forget to leave a empty "" as the first element of the array,
This is because the date is given by the system in a natural numbers format (1,2,3...) rather than a zero-starting format (0,1,2,3...), which the C array uses to index...
so the C array indexes the days as ""-0, "Monday"-1, "Tuesday"-2 etc. and the months as ""-0, "January"-1, "February"-2 etc.)

Label positioning

The locational placement in LVGL is done on a cartesian plane, where each object can have dynamic origin placement, and the Y-axis is inverted... So going down is done with a positive Y-axis value and not negative as the it is by de-facto...

The position of the various objects in clock.cpp are set by the line,

lv_obj_set_pos(<obj>, <new_x>, <new_y>)

and the top left corner is the Cartesian origin, aka coordinates (0,0)

we use another function, that is more advanced that gives the positional alignment based on preset locations...

lv_obj_align(<text/obj>, <image/obj>, <location_parameter>, <new_x>, <new_y>);

the "<image/obj>" data is used for putting text beside other picture icons , and so if using only text based labels, we can substitute it with,

lv_scr_act() (or) NULL

<new_x>, <new_y> are the cartesian coordinates, <location parameter> is replaced by LV_ALIGN_<preset>, there will be a picture showing the presets below, and <text/obj> is your text label...

here, LV_ALIGN_<preset> sets the cartesian origin...

Label positioning based on alignment is both a simple and complicated thing to understand, so here I have given something you can refer to while modifying the position of the various labels and objects...

you can also refer here for LVGL's documentation of coordinate system https://docs.lvgl.io/v6/en/html/object-types/obj.html#coordinates

It is however recommended that you use the first method to set the location

lv_obj_set_pos(<obj>, <new_x>, <new_y>)

as it is simple and easier for beginners

Here is a small example.

Take the Label that tells the date, In the source file (clock.cpp) it is this line,

lv_obj_align(label_date, lv_scr_act(), LV_ALIGN_IN_LEFT_MID, 0, 60);

by increasing the Value of the Y coordinate (60) to a higher value, we can bring the position of the Date downwards a bit away from the Time, and toward the Heartbeat count in the bottom row here I will increase it to 80, so it becomes..

lv_obj_align(label_date, lv_scr_act(), LV_ALIGN_IN_LEFT_MID, 0, 80);

and now we have made some space up top..

now let's try something a bit complex,

Take the position argument for the label that tells you time... here, in the source file (clock.cpp),

lv_obj_align(label_time, lv_scr_act(), LV_ALIGN_IN_LEFT_MID, 0, 0);

this line determines the position of the Label telling time, as seen in the image...

we modifying this, by changing the origin <preset> parameter (here it is LV_ALIGN_IN_LEFT_MID) to LV_ALIGN_IN_TOP_LEFT

you can alternatively swap the whole line to,

lv_obj_set_pos(label_time, 0, 0);

this makes the Time label/obj. to go to the top left corner...

but I will do something a little extra, I will modify the label that store the data and Time format, i.e this line,

sprintf(timeStr, "%c%c:%c%c", hoursChar[0],hoursChar[1],minutesChar[0], minutesChar[1]);

by removing the ":" colon in between the numbers, and replacing it with a Newline symbol "\n" I change it to become,

sprintf(timeStr, "%c%c\n%c%c", hoursChar[0],hoursChar[1],minutesChar[0], minutesChar[1]);

this gives it a nice wrapped text format in the top corner, and gives us some space to play with in the side, for things like Pictures and icons, which we will do next..

If you have been able to do these things, you now have completed the 2nd part of the tutorial, and now know how to change and modify the position of labels..

Using icons

The LVGL library allows for the use of widgets known as "Images", In short it allows you to use small Icons like pictures with a small dedicated function, However when this was attempted the first time we stumbled on some problems as LVGL v6 (used on the pinetime) is not much documented as the latest release (v7 as of August 2020) but also the existing code was only documented for C not C++, after some painful attempts we were able to translate it into C++,

To bring images into Clock.cpp you will need to do the following,

1. Have a small image that cannot exceed a maximum size of 240px x 240px (pinetime max resolution)

2. Use this Image converter (Thanks to LVGL) https://lvgl.io/tools/imageconverter to convert your image to a C array and having the Color format as "True color" and the output format as "C array" make sure to use something simple as the name we will be using "bitmap" as the name, but will also be referred as <name> for simplicity

Note: for example we shall use <name> = bitmap, but any simple word can be used, as long as it does not cause problems with system variables

Image size considerations

since the image will be written from internal Flash to the RAM, we need to be considerate as to use less RAM as we are capped at 64KB maximum... for testing we did not exceed more than 30% of the 64KB which is about 19.2KB...

You can calculate the RAM usage of your images with a simple formula..

<picture_X> x <picture_Y> x 2 

give you the number of KB the image uses... where, <picture_X> <picture_Y> are the dimensions of the image horizontally and vertically

for example,

if <picture_X>=80px <picture_Y>=64px

then,

total RAM used = 80 x 60 x 2 = 10.24KB 

please use the RAM sparingly, too much and the RAM overflow could cause the MCU to crash... you have been warned !!!

Preparing the image for inclusion as an icon

Once you have your obtained your C array from the LVGL converter, you can take a look inside it to see all the different formats of your image, try using something like Notepad++ or any of your favorite text editors to peek inside of it,

there will be 4 sets of Arrays inside it that look like,

#if LV_COLOR_DEPTH == 1 || LV_COLOR_DEPTH == 8
 /*Pixel format: Red: 3 bit, Green: 3 bit, Blue: 2 bit*/
 0x00, 0x00, 0x00,...
...0x00, 0x00, 0x00, 
#endif

#if LV_COLOR_DEPTH == 16 && LV_COLOR_16_SWAP == 0
 /*Pixel format: Red: 5 bit, Green: 6 bit, Blue: 5 bit*/
 0x00, 0x00, 0x00,...
...0x00, 0x00, 0x00, 
#endif

#if LV_COLOR_DEPTH == 16 && LV_COLOR_16_SWAP != 0
 /*Pixel format: Red: 5 bit, Green: 6 bit, Blue: 5 bit BUT the 2 bytes are swapped*/
 0x00, 0x00, 0x00,...
...0x00, 0x00, 0x00, 
#endif

#if LV_COLOR_DEPTH == 32
 /*Pixel format: Fix 0xFF: 8 bit, Red: 8 bit, Green: 8 bit, Blue: 8 bit*/
 0x00, 0x00, 0x00,...
...0x00, 0x00, 0xff, 
#endif
};

And another small bit of info we will need for later that looks like,

const lv_img_dsc_t bitmap = {
 .header.always_zero = 0,
 .header.w = 40,
 .header.h = 40,
 .data_size = 1600 * LV_COLOR_SIZE / 8,
 .header.cf = LV_IMG_CF_TRUE_COLOR,
 .data = bitmap_map,
};

NOTE: There are some header files at the top, which we can ignore...

RGB565 image format

The Pinetime uses a display that uses a 16 bit color space, also known as RGB565.

These 16 bit are assigned to RGB as 5 bits each for Red and Blue and 6 bits for Green, so 5+6+5=16 bits are required, so each pixel's color occupies 2 bytes of data, and since 2¹⁶ is equal to 65,536 it allows us to view 65,536 or 65k colors

The way it packs these bits is by converting the bits into 2x 4+4 bit hex-code, so for example,

if the color of a pixel in Binary is 10110100 01011111 (this color is approximately Lavender purple)

It is split as 1011 & 0100 for the first byte and 0101 & 1111 for the second byte and so, converting the binary into Hex-code,

the two parts are 0xB4 and 0xF5

These two parts in conjunction are used for determining the color of one pixel...

also from the binary, it is observed that,

The bits 10110 is used for Red, 100010 is used for green, and 11111 is used for blue.

Flipping the bytes

The LVGL library has a feature that allows you to flip the two bytes of the pixel, so if the two parts were, ...0xB4,0xF5,... ,it will change it to become, ...0xF5,0xB4,...

The reason for this is to allow the use of 8-bit SPI interfaces, but we do not require it, and if set with wrong parameter we could get problems with the color...

To make sure you are ready for the next step, make sure that inside your lvgl configuration file (located at src/libs/lv_conf.h)

this parameter,

#define LV_COLOR_16_SWAP   0

is set to "0" as seen...

Using git to work on the firmware

Testing the firmware

Installing the new firmware

A holistic guide on how to install different firmware using various hardware programmers is available here: Reprogramming the PineTime. There's also the possibility of using OTA updating. //TODO: add that to the article!