xor pattern shader (the comment) :p

xor.vert.frag

#version 430
#extension GL_ARB_separate_shader_objects : enable

const vec2 vdata[] = vec2[] (
      vec2(1.0, 1.0),
      vec2(1.0, 0.0),
      vec2(0.0, 1.0),
      vec2(0.0, 0.0));

void main()
{
   gl_Position = vec4(vdata[gl_VertexIndex] * 2.0 - 1.0, 0.0, 1.0);
}

==================================================================
  
#version 450

/* layout(location = 0) in vec2 v_coords; */
layout(push_constant) uniform img_dims {
	float w;
	float h;
} IMG_DIMS;

layout(location = 0) out vec4 f_color;

/*
void main()
{
	int xor = (int(gl_FragCoord.x) ^ int(gl_FragCoord.y));
	float r = float((xor * 2) & 0xff) / 255.0;
	float g = float((xor * 4) & 0xff) / 255.0;
	float b = float((xor * 8) & 0xff) / 255.0;

	vec3 col = vec3(r, g, b);
	f_color = vec4(col, 1.0);
}
*/
const vec4 colors[] = vec4[] (
	vec4(1.0, 0.0, 0.0, 1.0),
	vec4(0.0, 1.0, 0.0, 1.0),
	vec4(0.0, 0.0, 1.0, 1.0),
	vec4(1.0, 1.0, 0.0, 1.0),
	vec4(1.0, 0.0, 1.0, 1.0),
	vec4(0.0, 1.0, 1.0, 1.0));

void main()
{
	int band = int(gl_FragCoord.x * 6.0 / IMG_DIMS.w);
	f_color = colors[band];
}