c++ Fade between colors? (Arduino)

问题:

I currently have this thats fading between 2 set colours:

for(int i=0;i<nLEDs;i++){
    a = (255 / 100) * (incomingByte * sensitivity);
    r = (r * 7 + a + 7) / 8;
    g = (g * 7 + (255 - a) + 7) / 8;
    b = 0;

    FTLEDColour col = { r , g , b };
    led.setLED(i, col);
  }

But now im trying to allow users to enter their own colours:

// > Colour fade, Start colour

int colFade1Red = 0;
int colFade1Green = 255;
int colFade1Blue = 0;

// > Colour fade, End colour

int colFade2Red = 255;
int colFade2Green = 0;
int colFade2Blue = 0;

int fadeAm = 7; // Fade speed

with the fading code:

void ColourFade(){
  for(int i=0;i<nLEDs;i++){

    r = ctest(colFade1Red, colFade2Red, r);
    g = ctest(colFade1Green, colFade2Green, g);
    b = ctest(colFade1Blue, colFade2Blue, b);

    FTLEDColour col = { r , g , b };
    led.setLED(i, col);
  }
}

int ctest(int col1, int col2, int cur){
   int temp = col1 - col2;
   if(temp < 0) { temp = -temp; } 

   int alp = (temp / 100) * (incomingByte * sensitivity);

   if(col1 < col2){
     return (cur * fadeAm + (col2 - alp) + fadeAm) / (fadeAm +1 );
   } else {
     return (cur * fadeAm + alp + fadeAm) / (fadeAm +1 );
   }
}

But this starts with the Second user colour and fades into pink. How would I fade colours properly?

Also "incomingByte" is a value between 0 and 100, and the code is in a update loop.

回答1:

Smooth transitions between colours is best done in a different colour space (IMHO).

As an example, to transition from bright red to bright green, do you want to go via bright yellow (around the edge of the colour wheel) or via #808000 (murky yellow) - which is what a straight line interpolation would give you in the RGB domain.

Having done this for my Moodlamp app, I used the HSL colour space. I specified a start colour and end colour, along with a number of steps for the transition to take. That enabled me to calculate how much to adjust H, S and L by at each point in the transition.

Only at the point of using the colour did I convert back to RGB.

You can see the javascript code here (please bear in mind it's the first Javascript I ever wrote, so if it seems non-idiomatic, that's probably why!):

https://github.com/martinjthompson/MoodLamp/blob/master/app/assistants/lamp-assistant.js

回答2:

It's impossible to fade to pink beacuse you are starting from red and ending with green.

To avoid this kind of mistake I suggest you to write an object oriented code.

If you don't want to write the classes to handle a 3D vectonr you can use the Arduino Tinker Library

I wrote this example for you:

#include <Vect3d.h>
#include <SerialLog.h>

Tinker::Vect3d<float> red(255,0,0);
Tinker::Vect3d<float> green(0,255,0);
Tinker::SerialLog serialLog;

void setup(){
  Serial.begin(9600);
  serialLog.display("Fade color example");  
  serialLog.endline();
}

void loop(){
  //fade factor computation
  const uint32_t t   = millis()%10000;
  const float cosArg = t/10000.*3.1415*2;
  const float fade   = abs(cos(cosArg));

  //Here's the color computation... as you can see is very easy to do!! :)
  Tinker::Vect3d<uint8_t> finalColor(red*fade + green*(1-fade));

  //We print the vect3d on the arduino serial port
  Tinker::LOG::displayVect3d(finalColor,&serialLog);
  serialLog.endline();
  delay(500);
}

Which prints the following output on the serial port

Fade color example
V[255;0;0]
V[242;12;0]
V[206;48;0]
V[149;105;0]
V[78;176;0]
V[0;254;0]
V[79;175;0]
V[150;104;0]
V[206;48;0]
V[242;12;0]
V[254;0;0]
V[242;12;0]
V[205;49;0]
V[148;106;0]
V[77;177;0]
V[1;253;0]
V[80;174;0]
V[151;103;0]

hope that this helps :)