Having trouble trying to smooth a gradient to use as ALPHA

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1

Godot Version

4.5

Question

I’m trying to create a very smooth gradient effect on a 3D object that will be attached to the camera in XR. I don’t want to use the built in vignette as I’ll be applying this to different effects and different eyes. This is a spatial shader.

I’m using a radial black to white gradient as a texture 2d and putting it into the ALPHA output of the shader, but it’s giving a much sharper distinction between the black and the transparent than I’d like.

e.g. This is what I would like to see - a very long transition between black to clear.

mockup
mockup646×490 48.4 KB

But this is what is actually happening:

In Godot
In Godot588×501 23.4 KB

Any ideas on how to smoothen that out? I’ve tried using an external file as a texture for the alpha but it’s the same.

Happy for visual / coded shader ideas

2

How do you calculate the falloff?

3

It’s not calculated it’s using a gradient resource in a texture2d attached to the alpha but happy to do it calculated if it would work better?

P.s. forgot to mention it’s using mobile renderer

4

Show your exact setup.

5

Thanks, although I’ve tried a few things, the shader is essentially - a black solid going into ALBEDO, and a radial gradiant going into ALPHA (multiplied by a float for changing opacity by script).

shader_type spatial;
render_mode depth_test_disabled, skip_vertex_transform, unshaded, cull_disabled;
uniform float fp = 1.0;
uniform sampler2D tex_frg_4;
// Modify VERTEX.xy using the projection matrix to correctly center the effect.
void vertex() {
        vec2 vert_pos = VERTEX.xy;

        if (length(vert_pos) < 0.99) {
                vec4 offset = PROJECTION_MATRIX * vec4(0.0, 0.0, 1.0, 1.0);
                vert_pos += (offset.xy / offset.w);
        }

        POSITION = vec4(vert_pos, 1.0, 1.0);
}

void fragment() {
	vec3 n_out5p0;
	vec3 n_in5p0 = vec3(0.00000, 0.00000, 0.00000);
	vec3 c = n_in5p0;
	float max1 = max(c.r, c.g);
	float max2 = max(max1, c.b);
	n_out5p0 = vec3(max2, max2, max2);
	float n_out7p0 = fp;

	vec4 n_out4p0 = texture(tex_frg_4, UV);
	float n_out6p0 = n_out4p0.x * n_out7p0;
		//if (VIEW_INDEX == VIEW_RIGHT) {
        ALBEDO =  vec3(0.0, 0.0, 0.0);
        ALPHA = n_out6p0;
//}
//else ALPHA = 0.0;
}

And the gradiant.tres I made which goes into “tex_frg_4” is setup like this.

g2a
g2a450×643 28.7 KB

Cheers

6

Switch texture interpolation color space to linear and interpolation mode to cubic.

You can further soften the falloff by adding the following as the last line:
ALPHA = pow(ALPHA, exponent);

exponent needs to be between 0.0 and 1.0

In general a better approach might be to use a curve texture. This will let you explicitly control the falloff using a curve but you’ll need to draw the circle in the shader. Something like:

float d = distance(UV, vec2(0.5)) * 2.0;
ALPHA = texture(your_curve_texture, vec2(d, 0.0)).r;
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