Starter fragment shader for basic repeatable lines

lines.frag

// ShaderToy Inputs
uniform vec3      iResolution;           // viewport resolution (in pixels)
uniform float     iGlobalTime;           // shader playback time (in seconds)

const float PI=3.14159265358979323846;

float round( float x ) {
	float val = mod( x, x );
	if( val >= 0.5 ){
		return ceil( x );
	}else{
		return floor( x );
	}
}


void main(void)
{
	vec2 uv = gl_FragCoord.xy / iResolution.xy;
		
	// draw vertical lines
	//float stripeVal = floor( mod(gl_FragCoord.x, 7.0) ) == 0.0  ? 1.0 : 0.0;
	//vec4 col = vec4( stripeVal ) * 0.5;
	
	// draw horizontal lines
	//float stripeVal = floor( mod( gl_FragCoord.y, 7.0 ) ) == 0.0  ? 1.0 : 0.0;
	//vec4 col = vec4( stripeVal ) * 0.5;
	
	// draw large round checkerboard
	//float stripeVal = cos( gl_FragCoord.x * 0.1 ) + sin( gl_FragCoord.y * 0.1 );
	//vec4 col = vec4( stripeVal ) * 0.5;
	
	
  	// draw diagonal lines
  
	// rotating diagonal
	//float t = iGlobalTime * 0.5;
	
	// perfectly diagonal
	float t = PI / 4.0;	

	float w = 2.0;			  // width (larger value = smaller width)
	float stripeVal = cos( ( gl_FragCoord.x * cos( t ) * w ) + ( gl_FragCoord.y * sin( t ) * w ) ); 
	stripeVal = clamp( round( stripeVal ), -1.0, 0.0 );   // clamping gets rid of the random white lines	
	
	vec4 col = vec4( stripeVal ) * 0.1;	// contrast
	col += vec4( 0.04, 0.6, 1.0, 1.0 );	  // color
	gl_FragColor = col;
}