3D Radial Motion Blur Shader For Propellers and Wheels

How to use:

get the addon for 4.2 here (should be compatible with newer versions)

follow this video’s tutorial section for setup

the demo I have included has the radial motion blur as part of the general motion blur implementation, and you can see an example of it used with the toy windmills 

Shader code

shader_type spatial;

render_mode unshaded, depth_draw_always, fog_disabled;

uniform sampler2D screen_texture : hint_screen_texture, filter_nearest;
uniform sampler2D depth_texture : hint_depth_texture, filter_nearest;

uniform vec3 local_rotation_axis = vec3(0, 1, 0);

uniform float rotation_speed = 0;

uniform int sample_count = 8;

uniform float shape_depth = 1;

uniform float shape_radius = 1;

uniform float shape_axis_offset = 0;

uniform float debug_toggle = 0;

uniform vec4 debug_color : source_color = vec4(0);

//https://www.shadertoy.com/view/fdtfWM
vec3 rotate(float angle, vec3 axis, vec3 point) // NOTE: axis must be unit!
{
    float c = cos(angle);
    float s = sin(angle);
    return c * point + s * cross(axis, point) + (1.0 - c) * (dot(point, axis) * axis); // Rodrigues' Rotation Formula
}

// from https://www.shadertoy.com/view/ftKfzc
float interleaved_gradient_noise(vec2 uv, int FrameId){
	uv += float(FrameId)  * (vec2(47, 17) * 0.695);

    vec3 magic = vec3( 0.06711056, 0.00583715, 52.9829189 );

    return fract(magic.z * fract(dot(uv, magic.xy)));
}

vec3 get_projection_onto_plane(vec3 plane_origin, vec3 normal, vec3 vector)
{
	float plane_distance = dot(plane_origin, normal);
	return vector * plane_distance / dot(normal, vector);
}

float soft_depth_compare(float x, float y, float sze)
{
	return clamp(1. - (x - y) / sze, 0., 1.);
}

vec2 intersect_cylinder(vec3 eye_point, vec3 end_point, vec3 origin, vec3 axis, float radius)
{
	eye_point -= axis * dot(eye_point - origin, axis) + origin;

	end_point -= axis * dot(end_point - origin, axis) + origin;

	vec3 direction = end_point - eye_point;

	float A = dot(direction, direction);
	float B = 2. * dot(eye_point, direction);
	float C = dot(eye_point, eye_point) - radius * radius;

	float square_component = sqrt(B * B - 4. * A * C);

	return vec2(-B + square_component, -B - square_component) / (2. * A);
}

vec2 within_cylinder(vec3 point, vec3 origin, vec3 axis, float radius, float depth, float axis_offset)
{
	float within_depth = step(abs(dot(point - origin - axis * axis_offset, axis)), depth / 2.);
	vec3 perpendicular_component = point - axis * dot(axis, point - origin) - origin;
	float within_radius = step(dot(perpendicular_component, perpendicular_component), radius * radius);

	return vec2(within_depth * within_radius, step(0, dot(point - origin, axis)));
}

vec3 color_corrected(vec3 color)
{
	return color / mix(
				pow((vec3(1.) + vec3(0.055)) * (1.0 / (1.0 + 0.055)), vec3(2.4)),
				vec3(1.) * (1.0 / 12.92),
				lessThan(vec3(1.), vec3(0.04045)));
}

void fragment() {
	vec2 screen_uv = SCREEN_UV;

	float depth = texture(depth_texture, screen_uv).x;
	vec3 ndc = vec3(screen_uv * 2.0 - 1.0, depth);
	vec4 world_position = INV_VIEW_MATRIX * INV_PROJECTION_MATRIX * vec4(ndc, 1.0);
	world_position.xyz /= world_position.w;

	vec4 world_mesh_position = INV_VIEW_MATRIX * INV_PROJECTION_MATRIX * vec4(screen_uv * 2.0 - 1.0, FRAGCOORD.z, 1.0);
	world_mesh_position.xyz /= world_mesh_position.w;

	vec3 node_relative_position = world_position.xyz - NODE_POSITION_WORLD;

	vec3 world_rotation_axis = normalize(mat3(MODEL_MATRIX) * local_rotation_axis);

	float axis_parallel_offset = dot(node_relative_position, world_rotation_axis);

	vec3 axis_parallel_component = axis_parallel_offset * world_rotation_axis;

	vec3 axis_perpendicular_component = node_relative_position - axis_parallel_component;

	float axis_perpendicular_offset = length(axis_perpendicular_component);

	vec3 camera_node_position = NODE_POSITION_WORLD - CAMERA_POSITION_WORLD;

	vec3 camera_cylinder_back_plane_origin = camera_node_position + world_rotation_axis * (clamp(axis_parallel_offset - shape_axis_offset, -shape_depth / 2., shape_depth / 2.) + shape_axis_offset);

	vec3 camera_relative_position = world_position.xyz - CAMERA_POSITION_WORLD;

	vec3 camera_plane_projected_results = get_projection_onto_plane(camera_cylinder_back_plane_origin, world_rotation_axis, camera_relative_position);

	vec2 world_cylinder_intersect_result = intersect_cylinder(CAMERA_POSITION_WORLD, camera_plane_projected_results + CAMERA_POSITION_WORLD, NODE_POSITION_WORLD, world_rotation_axis, shape_radius);

	float lands_within_cylinder = step(1, world_cylinder_intersect_result.x);

	camera_plane_projected_results *= mix(world_cylinder_intersect_result.x, 1, lands_within_cylinder);

	vec3 node_cylinder_clamped_result = camera_plane_projected_results - camera_node_position;

	float on_mesh = 1.;

	vec3 raw_clamed_difference = node_cylinder_clamped_result - node_relative_position;

	if(dot(raw_clamed_difference, raw_clamed_difference) > 0.001)
	{
		node_relative_position = world_mesh_position.xyz - NODE_POSITION_WORLD;
		on_mesh = 0.;
	}

	float noise_variation = interleaved_gradient_noise(SCREEN_UV * vec2(textureSize(screen_texture, 0)), int(TIME * 100.)) / float(sample_count);

	float sum = 1.;

	vec4 base_sample = texture(screen_texture, screen_uv);

	vec4 col = base_sample;

	vec2 nearest_ahead_of_mesh_uv = screen_uv;

	float nearest_ahead_of_mesh_set = 0.;

	vec2 past_mesh_uv_found = screen_uv;

	float was_mesh_uv_found = 0.;

	vec3 camera_relative_position_normalized = normalize(node_relative_position.xyz + camera_node_position);

	for(int i = 0; i < sample_count; i++)
	{
		float angle = (float(i) / float(sample_count) + noise_variation) * rotation_speed;

		vec3 node_rotated_sample = rotate(-angle, world_rotation_axis.xyz, node_relative_position.xyz);

		vec4 current_ndc = (PROJECTION_MATRIX * VIEW_MATRIX * (vec4(node_rotated_sample, 1) + vec4(NODE_POSITION_WORLD, 0)));

		current_ndc.xyz /= current_ndc.w;

		vec2 current_uv_sample = ((current_ndc + 1.) / 2.).xy ;

		float current_depth = texture(depth_texture, current_uv_sample).x;

		vec4 current_world_position = INV_VIEW_MATRIX * INV_PROJECTION_MATRIX * vec4(vec3(current_ndc.xy, current_depth), 1.0);

		current_world_position.xyz /= current_world_position.w;

		vec3 current_camera_unrotated_position = rotate(angle, world_rotation_axis.xyz, current_world_position.xyz - NODE_POSITION_WORLD) + camera_node_position;

		vec3 current_unrotated_perpendicular_component = current_camera_unrotated_position - camera_relative_position_normalized * dot(current_camera_unrotated_position, camera_relative_position_normalized);

		float current_unrotated_perpendicular_offset = length(current_unrotated_perpendicular_component);

		current_depth = 0.05 / current_depth;

		float current_sample_depth = 0.05 / current_ndc.z;

		vec2 current_sample_inside_cylinder = within_cylinder(current_world_position.xyz, NODE_POSITION_WORLD, world_rotation_axis, shape_radius, shape_depth, shape_axis_offset);

		float occluding_mesh = soft_depth_compare(current_depth + 0.1, current_sample_depth, 0.1) * (1. - current_sample_inside_cylinder.x);

		float choose_best_uv = on_mesh * (1. - current_sample_inside_cylinder.x);

		current_uv_sample = mix(screen_uv, current_uv_sample, 1. - (1. - current_sample_inside_cylinder.x) * (1. - on_mesh));

		current_uv_sample = mix(current_uv_sample, past_mesh_uv_found, occluding_mesh);

		current_uv_sample = mix(current_uv_sample, nearest_ahead_of_mesh_uv, nearest_ahead_of_mesh_set * choose_best_uv);

		if (current_uv_sample.x < 0. || current_uv_sample.x > 1. || current_uv_sample.y < 0. || current_uv_sample.y > 1.)
		{
			continue;
		}

		nearest_ahead_of_mesh_uv = mix(nearest_ahead_of_mesh_uv, current_uv_sample, (1. - nearest_ahead_of_mesh_set) * choose_best_uv);

		nearest_ahead_of_mesh_set = mix(nearest_ahead_of_mesh_set, 1., (1. - nearest_ahead_of_mesh_set) * choose_best_uv);

		past_mesh_uv_found = mix(current_uv_sample, past_mesh_uv_found, current_sample_inside_cylinder.x);

		was_mesh_uv_found = mix(1, was_mesh_uv_found, current_sample_inside_cylinder.x);

		float unrotated_sample_within_perpendicular_range = step(current_unrotated_perpendicular_offset, 0.1);

		float on_mesh_in_front = on_mesh * (1. - soft_depth_compare(current_sample_depth - 0.02, current_depth, 0.01)) * (1. - unrotated_sample_within_perpendicular_range);

		float weight = 1. - on_mesh_in_front * (1. - debug_toggle);
		//weight = 1. - (1. - was_mesh_uv_found) * (occluding_mesh);
		sum += weight;
		col += texture(screen_texture, current_uv_sample) * weight;
	}

	col /= sum;

	ALBEDO = col.xyz + debug_color.xyz;//vec3(depth * 10.);//
}

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