One short question, how can I fade efficiently between 2 RGB colors in a

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One short question, how can I fade efficiently between 2 RGB colors in a specific time? Is there a special function available?

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There’s no function with a built-in time element for this. However, if you look at the ‘blend’ functions you’ll see that you can easily specify a starting color, and an ending color, and then tell it basically what fraction of start and end you want mixed to produce the output. Blend functions are defined in FastLED, in colorutils.h and .cpp (e.g. https://github.com/FastLED/FastLED/blob/FastLED3.1/colorutils.h and .cpp )

So

CRGB start = CRGB::Blue;
CRGB end = CRGB::Green;

then make a loop that takes the amount of time that you want. Each time through the loop, calculate what ‘fraction’ of the way you are through the transition as a value from 0-255 (we’ll call that variable ‘frac’). In the body of that loop, you can then just do this:

CRGB current = blend( start, end, frac);

and ‘current’ will be the right color for this exact point in time.

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Thanks Mark!