The Best Darn Grid Shader (Yet) for Godot

I added ability to set a background color, as well as alpha channel.

shader_type spatial;

uniform int scale_0 : hint_range(1, 1024, 1);
uniform int scale_1 : hint_range(1, 1024, 1);

uniform float line_scale_0 : hint_range(0.001, 1, 0.001);
uniform float line_scale_1 : hint_range(0.001, 1, 0.001);

uniform vec4 color_0 : source_color;
uniform vec4 color_1 : source_color;

uniform vec4 background_color : source_color;

float pristineGrid( vec2 uv, vec2 lineWidth)
{
  vec2 ddx = dFdx(uv);
  vec2 ddy = dFdy(uv);
	
  vec2 uvDeriv = vec2(length(vec2(ddx.x, ddy.x)), length(vec2(ddx.y, ddy.y)));
  bvec2 invertLine = bvec2(lineWidth.x > 0.5, lineWidth.y > 0.5);
	
  vec2 targetWidth = vec2(
   invertLine.x ? 1.0 - lineWidth.x : lineWidth.x,
   invertLine.y ? 1.0 - lineWidth.y : lineWidth.y
   );
	
  vec2 drawWidth = clamp(targetWidth, uvDeriv, vec2(0.5));
  vec2 lineAA = uvDeriv * 1.5;
  vec2 gridUV = abs(fract(uv) * 2.0 - 1.0);
	
  gridUV.x = invertLine.x ? gridUV.x : 1.0 - gridUV.x;
  gridUV.y = invertLine.y ? gridUV.y : 1.0 - gridUV.y;
	
  vec2 grid2 = smoothstep(drawWidth + lineAA, drawWidth - lineAA, gridUV);

  grid2 *= clamp(targetWidth / drawWidth, 0.0, 1.0);
  grid2 = mix(grid2, targetWidth, clamp(uvDeriv * 2.0 - 1.0, 0.0, 1.0));
  grid2.x = invertLine.x ? 1.0 - grid2.x : grid2.x;
  grid2.y = invertLine.y ? 1.0 - grid2.y : grid2.y;
  return mix(grid2.x, 1.0, grid2.y);
}

void vertex() 
{
	//UV = VERTEX.xz;
}

void fragment() 
{
	vec4 grid_0 = vec4(pristineGrid(UV * float(scale_0), vec2(line_scale_0)));
	vec4 grid_1 = vec4(pristineGrid(UV * float(scale_1), vec2(line_scale_1)));
	
	//calculate color given both grid colors mixed
	//pristineGrid returns 0 or 1, so it'll choose one grid color or the other
	vec4 gridsMixed = mix(grid_1 * color_1.rgba, grid_0 * color_0.rgba, grid_0);
	//whether we are drawing the background (1.0) or either grid (0.0)
	float drawBackground = clamp(1.0 - (1.0 * (grid_0.r + grid_1.r)), 0.0, 1.0);
	
	//mix colors of either grid and background, based on what we are drawing
	vec4 finalColorToDraw = mix(gridsMixed, background_color, drawBackground);
	ALBEDO = finalColorToDraw.rgb;
	ALPHA = finalColorToDraw.a;
}