// Tensor glyph (instanced ellipsoid) shader for stress/strain tensor visualization.
//
// Group 0: Camera uniform (view-projection, eye position) : same layout as mesh.wgsl.
// + ClipPlanes uniform (binding 4) + ClipVolume uniform (binding 6).
// Group 1: TensorGlyphUniform (scalar mapping params) + LUT texture + sampler.
// Group 2: Per-instance storage buffer (TensorInstance: pre-computed model matrix,
// normal matrix, scalar).
//
// Vertex input: the glyph sphere base mesh (position vec3, normal vec3 : full Vertex layout).
//
// Each instance is an ellipsoid defined by a pre-computed TRS model matrix. The
// normal matrix (inverse transpose of the 3x3 rotation-scale block) is also uploaded
// per-instance for correct shading on the anisotropically-scaled ellipsoid surface.
// Color is looked up from the LUT using either a per-instance scalar attribute or a
// sign-derived value (tension/compression).
struct Camera {
view_proj: mat4x4<f32>,
eye_pos: vec3<f32>,
_pad: f32,
};
struct ClipPlanes {
planes: array<vec4<f32>, 6>,
count: u32,
_pad0: u32,
viewport_width: f32,
viewport_height: f32,
};
struct ClipVolumeUB {
volume_type: u32,
_pad0: u32, _pad1: u32, _pad2: u32,
plane_normal: vec3<f32>,
plane_dist: f32,
box_center: vec3<f32>,
_padB0: f32,
box_half_extents: vec3<f32>,
_padB1: f32,
box_col0: vec3<f32>,
_padB2: f32,
box_col1: vec3<f32>,
_padB3: f32,
box_col2: vec3<f32>,
_padB4: f32,
sphere_center: vec3<f32>,
sphere_radius: f32,
};
// TensorGlyphUniform : 64 bytes.
struct TensorGlyphUniform {
has_scalars: u32, // 4 bytes (1 = use per-instance scalar field)
scalar_min: f32, // 4 bytes
scalar_max: f32, // 4 bytes
_pad0: f32, // 4 bytes
_pad1: array<vec4<f32>, 3>, // 48 bytes padding -- total 64 bytes
};
// Per-instance data : 128 bytes.
// model = pre-computed TRS transform for this ellipsoid instance (64 bytes).
// The normal columns encode the inverse-transpose of the 3x3 rotation-scale block
// (= R * diag(1/s)) needed for correct ellipsoid normals under anisotropic scaling.
// Each column is stored as vec4 (xyz = column, w = unused) for 16-byte alignment.
struct TensorInstance {
model_col0: vec4<f32>, // 16 bytes
model_col1: vec4<f32>, // 16 bytes
model_col2: vec4<f32>, // 16 bytes
model_col3: vec4<f32>, // 16 bytes
normal_col0: vec4<f32>, // 16 bytes
normal_col1: vec4<f32>, // 16 bytes
normal_col2: vec4<f32>, // 16 bytes
scalar: f32, // 4 bytes
_pad0: f32, // 4 bytes -- three scalar pads, NOT vec3 (which has align 16)
_pad1: f32, // 4 bytes
_pad2: f32, // 4 bytes
// Total: 128 bytes, stride 128
};
@group(0) @binding(0) var<uniform> camera: Camera;
@group(0) @binding(4) var<uniform> clip_planes: ClipPlanes;
@group(0) @binding(6) var<uniform> clip_volume: ClipVolumeUB;
fn clip_volume_test(p: vec3<f32>) -> bool {
if clip_volume.volume_type == 0u { return true; }
if clip_volume.volume_type == 1u {
return dot(p, clip_volume.plane_normal) + clip_volume.plane_dist >= 0.0;
}
if clip_volume.volume_type == 2u {
let d = p - clip_volume.box_center;
let local = vec3<f32>(
dot(d, clip_volume.box_col0),
dot(d, clip_volume.box_col1),
dot(d, clip_volume.box_col2),
);
return abs(local.x) <= clip_volume.box_half_extents.x
&& abs(local.y) <= clip_volume.box_half_extents.y
&& abs(local.z) <= clip_volume.box_half_extents.z;
}
let ds = p - clip_volume.sphere_center;
return dot(ds, ds) <= clip_volume.sphere_radius * clip_volume.sphere_radius;
}
@group(1) @binding(0) var<uniform> tg_uniform: TensorGlyphUniform;
@group(1) @binding(1) var lut_texture: texture_2d<f32>;
@group(1) @binding(2) var lut_sampler: sampler;
@group(2) @binding(0) var<storage, read> instances: array<TensorInstance>;
struct VertexIn {
// Glyph sphere base mesh uses the full Vertex layout (64 bytes stride).
// We only use position (location 0) and normal (location 1).
@location(0) position: vec3<f32>,
@location(1) normal: vec3<f32>,
@location(2) color: vec4<f32>, // unused -- here to match buffer stride
@location(3) uv: vec2<f32>, // unused
@location(4) tangent: vec4<f32>, // unused
@builtin(instance_index) instance_index: u32,
};
struct VertexOut {
@builtin(position) clip_pos: vec4<f32>,
@location(0) color: vec4<f32>,
@location(1) world_pos: vec3<f32>,
@location(2) world_nrm: vec3<f32>,
};
@vertex
fn vs_main(in: VertexIn) -> VertexOut {
var out: VertexOut;
let inst = instances[in.instance_index];
// Reconstruct mat4x4 from column vectors.
let model = mat4x4<f32>(inst.model_col0, inst.model_col1, inst.model_col2, inst.model_col3);
// Reconstruct normal matrix (mat3x3) from packed column vectors.
let normal_mat = mat3x3<f32>(inst.normal_col0.xyz, inst.normal_col1.xyz, inst.normal_col2.xyz);
let world_pos = model * vec4<f32>(in.position, 1.0);
let world_nrm = normalize(normal_mat * in.normal);
out.clip_pos = camera.view_proj * world_pos;
out.world_pos = world_pos.xyz;
out.world_nrm = world_nrm;
// LUT lookup.
let scalar = inst.scalar;
let range = tg_uniform.scalar_max - tg_uniform.scalar_min;
let t = select(0.0, (scalar - tg_uniform.scalar_min) / range, range > 0.0);
let u = clamp(t, 0.0, 1.0);
out.color = textureSampleLevel(lut_texture, lut_sampler, vec2<f32>(u, 0.5), 0.0);
return out;
}
@fragment
fn fs_main(in: VertexOut) -> @location(0) vec4<f32> {
// Clip-plane culling.
for (var i = 0u; i < clip_planes.count; i = i + 1u) {
let plane = clip_planes.planes[i];
if dot(vec4<f32>(in.world_pos, 1.0), plane) < 0.0 {
discard;
}
}
if !clip_volume_test(in.world_pos) { discard; }
// Simple diffuse lighting with a fixed directional light.
let light_dir = normalize(vec3<f32>(0.3, 1.0, 0.5));
let n_dot_l = max(dot(in.world_nrm, light_dir), 0.0);
let ambient = 0.2;
let diffuse = 0.8 * n_dot_l;
let shading = ambient + diffuse;
return vec4<f32>(in.color.rgb * shading, in.color.a);
}