Implement Signed Distance Fields for 2D shaders

[reduz]

SDF Support

• 2D Occluder Polygons now have the option to become geometry to generate the SDF
• New functions added to 2D shaders:

vec2 screen_uv_to_sdf(vec2 screen_uv);
vec2 sdf_to_screen_uv(vec2 sdf_pos);
float texture_sdf(vec2 sdf_pos);
vec2 texture_sdf_normal(vec2 sdf_pos);

SDF operates in screen-relative global coordinates (pre-canvas transform), so its easy to measure distances in your shaders, as they use the same units as your game.

Example:

The following shader allows to make long drop shadows.

Code:

shader_type canvas_item;
render_mode unshaded;

uniform vec4 color : hint_color;
uniform float angle : hint_range(0,360);
uniform float len : hint_range(0,1000) = 300;
uniform float fade_margin : hint_range(0,100) = 5;

void fragment() {
	
	float ang_rad = angle * 3.1416 / 360.0;
	vec2 dir = vec2(sin(ang_rad),cos(ang_rad));
	float max_dist = len;
	vec2 at = screen_uv_to_sdf(SCREEN_UV);
	float accum = 0.0;
	
	while(accum < max_dist) {
	    float d = texture_sdf(at);
	    accum+=d;
	    if (d < 0.01) {
	        break;
	    }
	    at += d * dir;
	}
	float alpha = 1.0-min(1.0,accum/max_dist);
	if (accum < fade_margin) {
		alpha *= max(0.0,accum / fade_margin);
	}
	
	COLOR = vec4(color.rgb,alpha * color.a);
}

TODO

In the future it may be possible to optionally toggle a canvaslayer for sdf generation, so its not only limited to occluder polygons, but this will most likely have an increased cost, given rendering the screen oversized (like 1.x to 2.x the margins) is required to have useful SDFs (and this also requires more shader variants compiled). Most likely post 4.0 material.

[starry-abyss]

Can this implementation also be used to smooth edges of vector shapes?

[reduz]

@starry-abyss no, while it is possible to convert vector shapes to SDF to some extent (and I would like to work on that at some point), that is something entirely different.

[akien-mga]

Thanks!

[dreamsComeTrue]

Will there be any documentation/sample/demo in the Godot's docs explaining SDFs for newbies, and also - their potential use cases?

[clayjohn]

@dreamsComeTrue Yes, we will work on docs and demos once the API is finalized. Expect them close to release.