show pre-cut gear, as a reference

src/bevel_gear.rs

@@ -1,6 +1,6 @@
 use std::f32::consts::PI;
 
-use glam::{Affine3A, Vec2, Vec3, Vec3Swizzles, vec3};
+use glam::{Affine3A, Vec2, Vec3, Vec3Swizzles, vec2, vec3};
 
 use crate::{crown_gear::CrownGearDesc, profile::Profile, render::mesh::MeshIndexed};
 
@@ -30,6 +30,15 @@ impl BevelGearDesc {
 	pub fn pitch_distance(&self) -> f32 {
 		self.pitch_radius() / self.cone_halfangle.tan()
 	}
+
+	/// Projects a point, expressed as a distance from the pitch circle (perpendicular to the pitch cone), onto the pitch plane.
+	/// Returns the distance from the pitch circle center to the projection.
+	fn project(&self, add: f32) -> f32 {
+		let dir = Vec2::from_angle(self.cone_halfangle);
+		let pt = vec2(self.pitch_radius(), 0.) + dir * add;
+		let r = pt.x / (1. - pt.y / self.pitch_distance());
+		r
+	}
 }
 
 #[derive(Debug, Clone)]
@@ -40,13 +49,29 @@ pub struct BevelGearShape {
 
 impl BevelGearShape {
 	pub fn new_blank(desc: &BevelGearDesc, n_points: usize) -> Self {
-		let r = 0.5 * desc.teeth as f32 + desc.profile.addendum + 0.1;
+		let r = desc.project(desc.profile.addendum + 0.1);
 		BevelGearShape {
 			desc: *desc,
 			points: vec![r; n_points],
 		}
 	}
 
+	pub fn new_cut(desc: &BevelGearDesc, n_points: usize) -> Self {
+		let cutter = desc.cutter();
+		let points = (0..n_points)
+			.map(|k| {
+				let t = k as f32 / n_points as f32;
+				let tooth = t * desc.teeth as f32;
+				let cut_depth = cutter.profile.y_from_tooth(-tooth);
+				desc.project(-cut_depth)
+			})
+			.collect();
+		BevelGearShape {
+			desc: *desc,
+			points,
+		}
+	}
+
 	pub fn to_points(&self) -> impl Iterator<Item = Vec2> {
 		let angle = 2.0 * PI / self.points.len() as f32;
 		self.points

src/lib.rs

@@ -64,10 +64,13 @@ pub struct Core {
 	depth: wgpu::Texture,
 
 	mesh_pipeline: render::mesh::Pipeline,
+	mesh_pipeline_translucent: render::mesh::Pipeline,
 
+	mesh_gear_precut: render::mesh::GpuMeshIndexed,
 	mesh_cutter: render::mesh::GpuMeshIndexed,
 
 	params_gear: render::mesh::GpuParams,
+	params_gear_precut: render::mesh::GpuParams,
 	params_cutter: render::mesh::GpuParams,
 
 	bevel_gear_desc: bevel_gear::BevelGearDesc,
@@ -111,6 +114,7 @@ impl Core {
 
 		let depth = Self::create_depth_buffer(&device, pixel_size);
 		let mesh_pipeline = render::mesh::Pipeline::new(&device);
+		let mesh_pipeline_translucent = render::mesh::Pipeline::new_translucent(&device);
 
 		let bevel_gear_desc = bevel_gear::BevelGearDesc {
 			profile: Default::default(),
@@ -119,6 +123,18 @@ impl Core {
 		};
 		let bevel_gear_shape =
 			bevel_gear::BevelGearShape::new_blank(&bevel_gear_desc, 16 * args.tooth as usize);
+		let bevel_gear_mesh = bevel_gear::make_mesh(
+			&bevel_gear_desc,
+			&bevel_gear::BevelGearVisual {
+				pad_in: 4.,
+				pad_out: 0.,
+			},
+			&bevel_gear::BevelGearShape::new_cut(&bevel_gear_desc, 16 * args.tooth as usize),
+		)
+		.to_mesh()
+		.to_standard_mesh()
+		.into_indexed();
+		let mesh_gear_precut = render::mesh::GpuMeshIndexed::new(&device, &bevel_gear_mesh);
 
 		let crown_gear_desc = bevel_gear_desc.cutter();
 		let crown_gear_mesh = crown_gear::make_mesh_simple(
@@ -138,6 +154,7 @@ impl Core {
 		let mesh_cutter = render::mesh::GpuMeshIndexed::new(&device, &crown_gear_mesh);
 
 		let params_gear = GpuParams::new(&device, &mesh_pipeline);
+		let params_gear_precut = GpuParams::new(&device, &mesh_pipeline_translucent);
 		let params_cutter = GpuParams::new(&device, &mesh_pipeline);
 
 		Self::configure_surface(&surface, &device, pixel_size);
@@ -148,8 +165,11 @@ impl Core {
 			surface,
 			depth,
 			mesh_pipeline,
+			mesh_pipeline_translucent,
 			mesh_cutter,
+			mesh_gear_precut,
 			params_gear,
+			params_gear_precut,
 			params_cutter,
 			bevel_gear_desc,
 			bevel_gear_shape,
@@ -159,13 +179,13 @@ impl Core {
 	}
 
 	fn gear_tfm(&self) -> Affine3A {
-		let turns = -self.t / self.bevel_gear_desc.teeth as f32;
+		let turns = 0.5 - self.t / self.bevel_gear_desc.teeth as f32;
 		Affine3A::from_rotation_translation(Quat::from_rotation_z(2. * PI * turns), Vec3::ZERO)
 	}
 
 	fn cutter_tfm(&self) -> Affine3A {
 		let skip_teeth = self.crown_gear_desc.pitch_radius.floor();
-		let turns = (self.t.fract_gl() + skip_teeth) / self.crown_gear_desc.teeth();
+		let turns = (self.t.fract_gl() - skip_teeth) / self.crown_gear_desc.teeth();
 		Affine3A::from_rotation_translation(
 			Quat::from_rotation_y(FRAC_PI_2 + self.bevel_gear_desc.cone_halfangle)
 				* Quat::from_rotation_z(2. * PI * turns),
@@ -192,14 +212,14 @@ impl Core {
 		let view = Mat4::from_mat3(camera::rotation(-args.cam_yaw, -args.cam_pitch));
 		let light = vec3(0.7, 0.5, 1.0).normalize();
 
-		self.mesh_pipeline.set_params(
-			&self.queue,
-			render::mesh::SceneParams {
-				projection: proj * view,
-				light,
-				_zero: 0.,
-			},
-		);
+		let scene_params = render::mesh::SceneParams {
+			projection: proj * view,
+			light,
+			_zero: 0.,
+		};
+		self.mesh_pipeline.set_params(&self.queue, scene_params);
+		self.mesh_pipeline_translucent
+			.set_params(&self.queue, scene_params);
 
 		self.params_gear.set(
 			&self.queue,
@@ -208,6 +228,13 @@ impl Core {
 				color: srgba_to_linear(vec4(0.2, 0.8, 0.1, 1.0)),
 			},
 		);
+		self.params_gear_precut.set(
+			&self.queue,
+			render::mesh::ObjectParams {
+				transform: self.gear_tfm().into(),
+				color: 0.3 * srgba_to_linear(vec4(0.1, 0.2, 0.8, 1.0)),
+			},
+		);
 		self.params_cutter.set(
 			&self.queue,
 			render::mesh::ObjectParams {
@@ -259,6 +286,11 @@ impl Core {
 		self.mesh_cutter
 			.render(&mut pass, &self.mesh_pipeline, &self.params_cutter);
 		mesh_gear.render(&mut pass, &self.mesh_pipeline, &self.params_gear);
+		self.mesh_gear_precut.render(
+			&mut pass,
+			&self.mesh_pipeline_translucent,
+			&self.params_gear_precut,
+		);
 		drop(pass);
 		self.queue.submit(std::iter::once(encoder.finish()));
 	}

src/render/mesh.rs

@@ -103,6 +103,30 @@ impl GpuMeshIndexed {
 
 impl Pipeline {
 	pub fn new(device: &wgpu::Device) -> Self {
+		Self::new_any(
+			device,
+			wgpu::BlendState::REPLACE,
+			wgpu::DepthBiasState::default(),
+		)
+	}
+
+	pub fn new_translucent(device: &wgpu::Device) -> Self {
+		Self::new_any(
+			device,
+			wgpu::BlendState::PREMULTIPLIED_ALPHA_BLENDING,
+			wgpu::DepthBiasState {
+				constant: -2,
+				slope_scale: -1. / 32.,
+				clamp: 0.,
+			},
+		)
+	}
+
+	fn new_any(
+		device: &wgpu::Device,
+		blend: wgpu::BlendState,
+		depth_bias: wgpu::DepthBiasState,
+	) -> Self {
 		let shader = device.create_shader_module(wgpu::ShaderModuleDescriptor {
 			label: None,
 			source: wgpu::ShaderSource::Wgsl(SHADER.into()),
@@ -141,7 +165,7 @@ impl Pipeline {
 				depth_write_enabled: true,
 				depth_compare: wgpu::CompareFunction::LessEqual,
 				stencil: wgpu::StencilState::default(),
-				bias: wgpu::DepthBiasState::default(),
+				bias: depth_bias,
 			}),
 			multisample: wgpu::MultisampleState {
 				count: 1,
@@ -154,7 +178,7 @@ impl Pipeline {
 				compilation_options: wgpu::PipelineCompilationOptions::default(),
 				targets: &[Some(wgpu::ColorTargetState {
 					format: crate::render::OUTPUT_FORMAT,
-					blend: Some(wgpu::BlendState::REPLACE),
+					blend: Some(blend),
 					write_mask: wgpu::ColorWrites::ALL,
 				})],
 			}),