silhouette.gdshader

shader_type spatial;
render_mode unshaded, blend_mul, depth_draw_never, depth_test_disabled;

// creates a silhouette that appears when the mesh is behind something else
// you can combine this with another material by assigning this as the Next Pass material
// this might need adjustment to work with 4.3 and later, because of the reversed depth

uniform vec3 shadow_colour:source_color = vec3(0.7,0.7,0.9);

uniform sampler2D depth_texture:hint_depth_texture;

/**
 * Minimum distance between wall and character before silhouette starts to appear
 */
uniform float min_threshold = 0.07;

/**
 * Distance between wall and character where silhouette reaches full opacity
 */
uniform float max_threshold = 0.08;

// because there wasn't an easy way to just flip the depth testing, I used a depth comparison based on this:
// https://github.com/danilw/godot-utils-and-other/blob/03bbe5112377040506d4498a1c5cc91bdda5f5cf/graphic_demo_3d/game/models/objects/spheres/shield.shader#L48


float linearize(float zdepth) {
	return 1.0 / zdepth;
}

void fragment() {
	float zdepth = linearize(texture(depth_texture, SCREEN_UV).x);
	float zpos = linearize(FRAGCOORD.z);
	float diff = zpos - zdepth; //difference between two depths
	float mix_val = smoothstep(min_threshold, max_threshold, diff);
	ALBEDO.rgb = mix(vec3(1.0), shadow_colour, mix_val);
}