framework-arduinoteensy-cxx20/libraries/RA8875/Examples/_UNO/moodBackground/moodBackground.ino

/*
  Modulate background color

 */
#include <SPI.h>
#include <RA8875.h>



#define RA8875_CS 10

#define RA8875_RESET 9//any pin or nothing!

RA8875 tft = RA8875(RA8875_CS, RA8875_RESET);


float angle;

void setup()
{
  tft.begin(RA8875_800x480);

}

// Translate a hue "angle" -120 to 120 degrees (ie -2PI/3 to 2PI/3) to
// a 6-bit R channel value
//
// This is very slow on a microcontroller, not a great example!
inline int angle_to_channel(float a) {
  if (a < -PI) a += 2 * PI;
  if (a < -2 * PI / 3  || a > 2 * PI / 3) return 0;
  float f_channel = cos(a * 3 / 4); // remap 120-degree 0-1.0 to 90 ??
  return ceil(f_channel * 255);//63
}

void loop() {
  uint16_t clr = (((angle_to_channel(angle - 4 * PI / 3) >> 1) & 0xF8) << 8) | (((angle_to_channel(angle - 2 * PI / 3)) & 0xFC) << 3) | ((angle_to_channel(angle) >> 1) >> 3);
  tft.fillWindow(clr);

  angle += 0.01;
  if (angle > PI)
    angle -= 2 * PI;
}