Help understanding noise texture 2D used with the "as normal map" option

[coordinatetm]

Godot Version

4.4.1-stable

Question

How do I use a NoiseTexture2D with 'as_normal_map' set, to set my normals in the fragment shader?

I’m currently using a noise texture 2d as a height map for some terrain I’m generating. It looks great.

I wanted to tackle normals for my terrain - I found this video online https://www.youtube.com/watch?v=-dMbacvrDrs that outlined the approach of duplicating your noise texture - with the duplicated one having the use as normal option enabled. I did this and followed through the video. I’m getting some convincing results, but it doesn’t quite feel right, and I have loads of questions:

Here’s the relevant code bits:

uniform sampler2D terrain_noise_normal_map_texture;

vec3 unpack_normalmap(vec4 rgba) {
	vec3 n = rgba.xyz * 2.0 - vec3(1.0);
	n.y *= -1.0;
	return n;
}

void fragment() {
	vec3 terrain_normal = normalize(unpack_normalmap(texture(terrain_noise_normal_map_texture, UV)));
	NORMAL = vec4(terrain_normal, 0.0).xyz; // This used to get multiplied by VIEW_MATRIX
}

Questions:

1. Why the need to unpack the normal map? why isn’t it in a godot native format?
2. How can I figure out the angle of the normal along the y-axis (positive-y being “height” for me) ? I had thought sampling the normal’s .y value would give me a 0->1.0 range of how far up the axis the normal is pointing, but this doesn’t look right
3. The original video I linked above contained a multiplication like so: NORMAL = (VIEW_MATRIX * vec4(terrain_normal, 0.0)).xyz;, however this seemed to cause the normals to change as my camera tilted up/down. Removing that multiplication removed this effect

[pennyloafers]

one you should enable the as normal in the noise texture, two your noise texture size should match the vertex count to make the noise pixel one-to-one with the vertexes. Three in your vertex function you should set the normal there, and this should carry over into the fragment shader. (which you probably don’t need anymore)

[coordinatetm]

Hey thanks for the reply.

I’m following through the advice - I’m setting the NORMAL in the vertex shader as you suggested:

NORMAL = texture(terrain_noise_normal_map_texture, UV).rgb;

and I’ve removed all references to NORMAL in my fragment shader. This results in no normals existing (no shadows being cast, surface looks flat) - any ideas?

[pennyloafers]

okay, I thought about it some more, and I guess noise as normal maps won’t work out like i thought. Basically the noise textures don’t work the way i thought and will require you to sample 3 points to determine the normal. here is an old tutorial.

also if you are bump mapping then you can apply to the NORMAL_MAP in the fragment shader. see reference

	NORMAL_MAP = texture(texture_normal, base_uv).xyz ;

[pennyloafers]

ah I think you just need to move your normal stuff in to the a vertex shader.

uniform sampler2D ter_noise;
uniform sampler2D ter_normal;
void vertex() {
	vec3 noise_tex = texture(ter_noise, UV).xyz;
	vec3 normal_tex = (texture(ter_normal, UV).xzy * 2.0 - vec3(1.0)) * vec3(1.0,1.0,-1.0);

	NORMAL = normalize(normal_tex);
	VERTEX += noise_tex.y ;
}

The more i play around with this the less it seems accurate.