Quick sky

This sky shader takes a regular texture and cleverly maps it onto the entire sky sphere. Any texture will work. For space, I’ve been using free images from the Hubble telescope

Repeat seams are blended too via textureSeamless()

Shader code

shader_type sky;

uniform sampler2D sky_tex : source_color;

uniform float energy : hint_range(0.0, 10.0, 0.1) = 1.0;
uniform float gamma : hint_range(0.0,4.0) = 1.0;
uniform sampler2D tint_ramp : source_color, repeat_disable, hint_default_white;
uniform vec3 scale = vec3(1);
uniform float triplanar_blend_power : hint_range(0.0,40.0) = 4.0;
uniform float seamless_blend : hint_range(0.0,0.5) = 0.1;

vec4 textureSeamless(sampler2D tex, vec2 uv, vec2 padding){
	vec2 inv_scale = 1.0 / (1.0 + 2.0 * padding);

	// Get partial derivatives here for textureGrad() to avoid mipmapping seams
	vec2 dx = dFdx(uv) * inv_scale;
	vec2 dy = dFdy(uv) * inv_scale;

	// Textures need to repeat somewhere. In addition, repeat must be enabled on the sampler
	uv = fract(uv+0.5)-0.5;

	// Get the bilinear blend factors. This is actually undefined for padding = 0
	vec2 u = smoothstep(-padding, padding, uv);

	// Apply scale
	uv *= inv_scale;

	// Bilinear interpolation
	inv_scale = 0.5 * (1.0 - inv_scale);
	vec4 lower_right = textureGrad(tex, uv - vec2(-1,-1) * inv_scale,  dx, dy);
	vec4 lower_left = textureGrad(tex, uv - vec2(1,-1) * inv_scale,  dx, dy);
	vec4 upper_right = textureGrad(tex, uv - vec2(-1,1) * inv_scale, dx, dy);
	vec4 upper_left = textureGrad(tex, uv - vec2(1,1) * inv_scale, dx, dy);

	lower_right = mix(lower_left, lower_right, u.x);
	upper_right = mix(upper_left, upper_right, u.x);

	return mix(upper_right, lower_right, u.y);
}

// "p" point being textured
// "n" surface normal at "p"
// "k" controls the sharpness of the blending in the transitions areas
// "s" texture sampler
vec4 boxmap( in sampler2D s, in vec3 p, in vec3 n, in float k )
{
    // project+fetch
    vec4 x = textureSeamless( s, p.yz, vec2(seamless_blend) );
    vec4 y = textureSeamless( s, p.zx, vec2(seamless_blend) );
    vec4 z = textureSeamless( s, p.xy, vec2(seamless_blend) );

    // blend weights
    vec3 w = pow( abs(n), vec3(k) );

    // blend and return
    return (x*w.x + y*w.y + z*w.z) / (w.x + w.y + w.z);
}

void sky() {
	// Ray direction
	vec3 rd = EYEDIR;
	
	// Apply scaling
	vec3 p = rd;
	p = normalize(rd / scale) * scale;
	vec3 n = normalize(p / scale);
	
	// Triplanar mapping of sky texture
	COLOR = boxmap(sky_tex, p, n, triplanar_blend_power).rgb;
	COLOR = energy * pow(COLOR, vec3(gamma));
	COLOR *= textureLod(tint_ramp, SKY_COORDS.yx, 0.0).rgb;
	
	// Alpha of tint ramp determines transparency of sky texture
	COLOR = mix(textureLod(tint_ramp, SKY_COORDS.yx, 0.0).rgb, COLOR, textureLod(tint_ramp, SKY_COORDS.yx, 0.0).a);
}

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