framework-arduinoteensy-cxx20/libraries/ILI9341_t3/examples/DemoSauce/TransitionScroll.h

#ifndef TRANSITION_SCROLL_H__
#define TRANSITION_SCROLL_H__

#include <Arduino.h>
#include "ILI9341_t3.h"
#include "MathUtil.h"
#include "BaseTransition.h"


const float TRANSITION_SCROLL_SPEED = 0.0014f;
const float SCROLL_WRAPS = 5.0f;

const uint_fast8_t MAX_STAGGER_X = 20;
const uint_fast8_t MAX_STAGGER_HEIGHT = 4;
const float STAGGER_X_STRENGTH = 100.0f;	// stagger is higher when the ease motion is faster


class TransitionScroll : public BaseTransition {
public:
	TransitionScroll() : BaseTransition() {};

  void init( ILI9341_t3 tft );
	void restart( ILI9341_t3 tft, uint_fast16_t color );
	void perFrame( ILI9341_t3 tft, FrameParams frameParams );
  boolean isComplete();

private:
	float _phase = 0;
	uint_fast16_t _color;
	float _lastEase;
	uint_fast16_t _lastScroll;
	uint16_t * _pixels;
};

void TransitionScroll::init( ILI9341_t3 tft ) {
	_pixels = (uint16_t*)malloc( sizeof(uint_fast16_t) * tft.width() );
}

void TransitionScroll::restart( ILI9341_t3 tft, uint_fast16_t inColor ) {
  //uint_fast16_t w = tft.width();
  //uint_fast16_t h = tft.height();
	_phase = 0;
	_color = inColor;
	_lastEase = 0;
	_lastScroll = tft.width();
}

float easeInOutCubic( float p ) {
  if( p < 0.5f ) {
    float p2 = p * 2.0f;
    return (p2*p2*p2) * 0.5f;
  }

  float p2 = (1.0f - p) * 2.0f;
  return 1.0f - (p2*p2*p2) * 0.5f;
}

float easeInOutQuart( float p ) {
  if( p < 0.5f ) {
    float p2 = p * 2.0f;
    return (p2*p2*p2*p2) * 0.5f;
  }

  float p2 = (1.0f - p) * 2.0f;
  return 1.0f - (p2*p2*p2*p2) * 0.5f;
}

void TransitionScroll::perFrame( ILI9341_t3 tft, FrameParams frameParams ) {
  uint_fast16_t w = (uint_fast16_t)tft.width();
  uint_fast16_t h = (uint_fast16_t)tft.height();

	_phase += frameParams.timeMult * TRANSITION_SCROLL_SPEED * SCROLL_WRAPS;

	// Apply some easing. Linear speed feels dull
	float ease = min( easeInOutCubic( _phase ), 1.0f );

	float unwrapped = SCROLL_WRAPS * ease;
	float wrap = unwrapped - floor(unwrapped);

	// scroll values fall from 1 to 0, so the image appears to move left.
	float scroll_f = w * (1.0f - wrap);
	uint_fast16_t scroll = floor(scroll_f);

	tft.setScroll( scroll );

	// Final frame: Fill with destination color
	if( unwrapped >= (SCROLL_WRAPS-1.0f) ) {
		if( scroll < _lastScroll ) {
			tft.fillRect( w - _lastScroll, 0, _lastScroll - scroll, h, _color );
			_lastScroll = scroll;
		}

		// Fill part of a random line
		uint_fast16_t x = random((uint_fast16_t)(w*0.9f),w);
		uint_fast16_t y = random(h);
		tft.drawFastHLine( x, y, w-x, _color );

	} else {
		// Let's noise this thing up
		uint_fast16_t staggerX = 1 + constrain( (ease-_lastEase) * STAGGER_X_STRENGTH, 0.0f, 1.0f ) * MAX_STAGGER_X;

		uint_fast8_t staggerHeight = random(1,MAX_STAGGER_HEIGHT+1);
		uint_fast16_t startY = random(h-(staggerHeight-1));

		for( uint_fast8_t line=0; line<staggerHeight; line++ ) {
			uint_fast16_t y = startY + line;
			tft.readRect( 0, y, w, 1, _pixels );
			tft.writeRect( staggerX, y, w-staggerX, 1, _pixels );
		}

	}

	_lastEase = ease;

}

boolean TransitionScroll::isComplete() {
  return _phase >= 1.0f;
}

#endif