Hi i'm sorry if this has already been answered.

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1

Hi i’m sorry if this has already been answered. I am struggling to find answers in this forum or on google. I have my WS2812B strip wrapped around the edge of a pool table. I want to have the animations start at the corner of the pool table but that is not where the strip starts. I think the easiest conceptual way of doing this is to have the beginning of the leds array to start at a different position other than 0.

Basically lets say the corner of the table is at leds[400] so I would like leds[0] to map to led number 400 and leds[1] map to led 401 and so on. Is there an easy way to either change the starting position of the leds array or shift the values in leds to a new array.

I hope this question makes sense. and somebody can point me in the right direction. Thank you

2

Here’s one way. Try something like this in your loop for testing and checking your offset:

for (uint16_t i=0; i<NUM_LEDS; i++) {
leds[(i+400) % NUM_LEDS] = CRGB:Green;
FastLED.show();
delay(100);
}
FastLED.clear();

Here’s info on modulo (%) if you haven’t seen it before.
https://www.arduino.cc/en/Reference/Modulo

Looking forward to photos/video of this pool table when you have it worked out. :slight_smile:

3

Another option (that uses a bit more memory) is to use a second array that you copy your leds data to with the offset before displaying. Here’s some example code:

4

@marmil ​ is right, the best way is to use modulo, once to get your head round how it works and the syntax it’s really useful…

5

Thanks for the quick responses guys! Thats really quick turn around.

The way I ended up doing it was creating a method called

int getRealPosition(int i){
if(i >= 88){
return i - 88; //88 is the number of LEDs from
//the end of the strip
}
return startPos+i; //startPos = NUM_LEDS-88
}

Now I call leds[getRealPosition(i)] = CRGB::Blue;

I may still try using modulo just for some more practice with it.