WeatherStar4000/server/styles/scss/shared/_scanlines.scss

/* REGULAR SCANLINES SETTINGS */

// width of 1 scanline (responsive units to prevent banding)
$scan-width: 1px;
$scan-width-scaled: 0.15vh; // viewport-relative unit for better scaling

// emulates a damage-your-eyes bad pre-2000 CRT screen ♥ (true, false)
$scan-crt: false;

// frames-per-second (should be > 1), only applies if $scan-crt: true;
$scan-fps: 20;

// scanline-color (rgba)
$scan-color: rgba(#000, .3);

// set z-index on 8, like in ♥ 8-bits ♥, or…
// set z-index on 2147483648 or more to enable scanlines on Chrome fullscreen (doesn't work in Firefox or IE);
$scan-z-index: 2147483648;

/* MOVING SCANLINE SETTINGS */

// moving scanline (true, false)
$scan-moving-line: true;

// opacity of the moving scanline
$scan-opacity: .75;

/* MIXINS */

// apply CRT animation: @include scan-crt($scan-crt);
@mixin scan-crt($scan-crt) {
	@if $scan-crt==true {
		animation: scanlines 1s steps($scan-fps) infinite;
	}

	@else {
		animation: none;
	}
}

// apply CRT animation: @include scan-crt($scan-crt);
@mixin scan-moving($scan-moving-line) {
	@if $scan-moving-line==true {
		animation: scanline 6s linear infinite;
	}

	@else {
		animation: none;
	}
}

/* CSS .scanlines CLASS */

.scanlines {
	position: relative;
	overflow: hidden; // only to animate the unique scanline

	&:before,
	&:after {
		display: block;
		pointer-events: none;
		content: '';
		position: absolute;
	}

	// unique scanline travelling on the screen
	&:before {
		// position: absolute;
		// bottom: 100%;
		width: 100%;
		height: $scan-width * 1;
		z-index: $scan-z-index + 1;
		background: $scan-color;
		opacity: $scan-opacity;
		// animation: scanline 6s linear infinite;
		@include scan-moving($scan-moving-line);
	}

	// the scanlines, so! - with responsive scaling for low-res displays
	&:after {
		top: 0;
		right: 0;
		bottom: 0;
		left: 0;
		z-index: $scan-z-index;
		// repeating-linear-gradient is more efficient than linear-gradient+background-size because it doesn't require the browser to calculate tiling
		background: repeating-linear-gradient(to bottom,
				transparent 0,
				transparent $scan-width,
				$scan-color $scan-width,
				$scan-color calc($scan-width * 2));
		@include scan-crt($scan-crt);

		// Prevent sub-pixel aliasing on scaled displays
		image-rendering: crisp-edges;
		image-rendering: pixelated;
	}

	// Scanlines use dynamic thickness calculated by JavaScript
	// JavaScript calculates optimal thickness to prevent banding at any scale factor
	// The --scanline-thickness custom property is set by applyScanlineScaling()
	// The modes (hairline, thin, medium, thick) force the base thickness selection
	// Some modes may appear the same (e.g. hairline and thin) depending on the display
	&:before {
		height: var(--scanline-thickness, $scan-width);
	}

	&:after {
		background: repeating-linear-gradient(to bottom,
				transparent 0,
				transparent var(--scanline-thickness, $scan-width),
				$scan-color var(--scanline-thickness, $scan-width),
				$scan-color calc(var(--scanline-thickness, $scan-width) * 2));
	}
}

/* ANIMATE UNIQUE SCANLINE */
@keyframes scanline {
	0% {
		transform: translate3d(0, 200000%, 0);
		// bottom: 0%; // to have a continuous scanline move, use this line (here in 0% step) instead of transform and write, in &:before, { position: absolute; bottom: 100%; }
	}
}

@keyframes scanlines {
	0% {
		background-position: 0 50%;
		// bottom: 0%; // to have a continuous scanline move, use this line (here in 0% step) instead of transform and write, in &:before, { position: absolute; bottom: 100%; }
	}
}