1// Aqua's motion-vector prepass.
2// Current geometry uses the shared forward deformation. Previous geometry is
3// evaluated at the same stable world anchor from the retained wave history.
4
5#import bevy_pbr::{
6    forward_io,
7    prepass_bindings,
8    mesh_functions,
9    prepass_io::{Vertex, VertexOutput, FragmentOutput},
10    mesh_view_bindings::view,
11    view_transformations::position_world_to_clip,
12}
13#import bevy_aqua_core::deform::{deform_current}
14#import bevy_render::globals::Globals
15#import aqua::cascade::{DEBUG_MODE_BEAUTY, DEBUG_MODE_FAR_TIER, MIN_SAMPLE_WEIGHT, begin_invocation, CascadeLayout, cascade_layout, far_tier_weight, field_params, lod_alpha, lod_count, owning_body, sample_field_flow, sample_field_level, surface, world_to_uv}
16#import bevy_aqua_core::river::river_analytic_displacement
17
18// Retained AnimWaves output and the exact layout/time/flow that produced it.
19struct AquaPreviousFrame {
20    previous_layout: CascadeLayout,
21    time: vec4<f32>,
22    flow: vec4<f32>,
23    valid: vec4<f32>,
24}
25@group(4) @binding(0) var aqua_previous_displacement: texture_2d_array<f32>;
26@group(4) @binding(1) var aqua_previous_sampler: sampler;
27@group(4) @binding(2) var<uniform> aqua_previous_frame: AquaPreviousFrame;
28@group(0) @binding(1) var<uniform> prepass_globals: Globals;
29
30fn previous_direct_displacement(world_xz: vec2<f32>, lod: u32) -> vec3<f32> {
31    // History contains the already-evolved wave field. Only global current
32    // advection remains to place that field in world space at the saved time.
33    let sampled_xz = world_xz
34        - aqua_previous_frame.flow.xy * aqua_previous_frame.time.x;
35    let previous_cascade = aqua_previous_frame.previous_layout.cascades[lod];
36    return textureSampleLevel(
37        aqua_previous_displacement,
38        aqua_previous_sampler,
39        world_to_uv(sampled_xz, previous_cascade),
40        i32(lod),
41        0.0,
42    ).xyz;
43}
44
45fn previous_near_displacement(
46    world_xz: vec2<f32>,
47    lod: u32,
48    alpha: f32,
49) -> vec3<f32> {
50    // LOD selection and weights describe today's mesh representation. History
51    // layout is used only to map the stable world sample into retained texels.
52    let smaller = cascade_layout.cascades[lod];
53    let bigger = cascade_layout.cascades[lod + 1u];
54    let smaller_weight = (1.0 - alpha) * smaller.weight;
55    let bigger_weight = (1.0 - smaller_weight) * bigger.weight;
56    var displacement = vec3(0.0);
57    if smaller_weight > MIN_SAMPLE_WEIGHT {
58        displacement += smaller_weight
59            * previous_direct_displacement(world_xz, lod);
60    }
61    if bigger_weight > MIN_SAMPLE_WEIGHT {
62        displacement += bigger_weight
63            * previous_direct_displacement(world_xz, lod + 1u);
64    }
65    return displacement;
66}
67
68fn previous_far_displacement(world_xz: vec2<f32>) -> vec3<f32> {
69    let outer_lod = lod_count() - 1u;
70    // Keep the current representation's outer-ring fade, but read its wave
71    // value from the retained outer history layer in the retained layout.
72    let weight = 1.0 - lod_alpha(
73        world_xz,
74        cascade_layout.cascades[outer_lod],
75    );
76    if weight <= MIN_SAMPLE_WEIGHT {
77        return vec3(0.0);
78    }
79    return weight * previous_direct_displacement(world_xz, outer_lod);
80}
81
82@vertex
83fn vertex(vertex_in: Vertex) -> VertexOutput {
84    var out: VertexOutput;
85    // The shared deform contract uses the forward vertex ABI. Translate the
86    // prepass input explicitly because Bevy assigns different attribute
87    // locations to the two stage ABIs.
88    var forward_vertex: forward_io::Vertex;
89    forward_vertex.instance_index = vertex_in.instance_index;
90    forward_vertex.position = vertex_in.position;
91#ifdef VERTEX_UVS_A
92    forward_vertex.uv = vertex_in.uv;
93#endif
94#ifdef VERTEX_UVS_B
95    forward_vertex.uv_b = vertex_in.uv_b;
96#endif
97#ifdef VERTEX_COLORS
98    forward_vertex.color = vertex_in.color;
99#endif
100#ifdef SKINNED
101    forward_vertex.joint_indices = vertex_in.joint_indices;
102    forward_vertex.joint_weights = vertex_in.joint_weights;
103#endif
104#ifdef MORPH_TARGETS
105    forward_vertex.index = vertex_in.index;
106#endif
107    let deformation = deform_current(forward_vertex, prepass_globals.time);
108    out.world_position = deformation.world_position;
109    out.position = position_world_to_clip(out.world_position.xyz);
110#ifdef MOTION_VECTOR_PREPASS
111    var previous_world_position = out.world_position;
112    // Do not touch history until it contains a completed prior AnimWaves frame.
113    if aqua_previous_frame.valid.x >= 0.5 {
114        if deformation.river {
115            // Re-evaluate only height at the saved time. XZ and the water level
116            // are current stable anchors, never a previous ring transform.
117            let previous_river = river_analytic_displacement(
118                deformation.sample_xz,
119                deformation.river_flow,
120                aqua_previous_frame.time.x,
121            );
122            previous_world_position = vec4(
123                deformation.sample_xz.x,
124                deformation.body_level + previous_river.x,
125                deformation.sample_xz.y,
126                1.0,
127            );
128        } else if !deformation.bounded {
129            let mode = u32(round(surface.debug.x));
130            let far_diagnostic = mode == DEBUG_MODE_FAR_TIER;
131            let far_tier = select(
132                0.0,
133                far_tier_weight(deformation.base_world_position),
134                mode == DEBUG_MODE_BEAUTY || far_diagnostic,
135            );
136            var previous_displacement: vec3<f32>;
137            if far_tier >= 1.0 {
138                previous_displacement = previous_far_displacement(
139                    deformation.sample_xz,
140                );
141            } else {
142                previous_displacement = previous_near_displacement(
143                    deformation.sample_xz,
144                    deformation.lod,
145                    deformation.sample_alpha,
146                );
147                if far_tier > 0.0 {
148                    previous_displacement = mix(
149                        previous_displacement,
150                        previous_far_displacement(deformation.sample_xz),
151                        far_tier,
152                    );
153                }
154            }
155            previous_world_position = vec4(
156                deformation.base_world_position + previous_displacement,
157                1.0,
158            );
159        }
160        // Bounded flat water intentionally retains current == previous.
161    }
162    out.previous_world_position = previous_world_position;
163#endif
164#ifdef VERTEX_OUTPUT_INSTANCE_INDEX
165    out.instance_index = vertex_in.instance_index;
166#endif
167#ifdef VISIBILITY_RANGE_DITHER
168    let world_from_local = mesh_functions::get_world_from_local(vertex_in.instance_index);
169    out.visibility_range_dither = mesh_functions::get_visibility_range_dither_level(
170        vertex_in.instance_index,
171        world_from_local[3],
172    );
173#endif
174    return out;
175}
176
177@fragment
178fn fragment(in: VertexOutput) -> FragmentOutput {
179    // Match forward coverage for the shared ocean/body tile set. In the main
180    // ocean showcase this is exactly the current forward runtime path.
181    var slot = 0u;
182    if field_params.info.x > 0.5 {
183        slot = u32(sample_field_level(in.world_position.xz).y + 0.5);
184    }
185    let bounded = slot > 0u;
186    if !bounded && field_params.info.y < 0.5 {
187        discard;
188    }
189    let params = owning_body(slot);
190    begin_invocation(bounded, params);
191    if bounded {
192        let distance_to_extent = length(
193            params.extent.xy - view.world_position.xz,
194        ) - params.extent.w;
195        if distance_to_extent > surface.far_tier.y {
196            discard;
197        }
198        let river_flow = sample_field_flow(in.world_position.xz);
199        if params.flags.y > 0.5 && river_flow.z < 0.0 {
200            discard;
201        }
202    }
203
204    var out: FragmentOutput;
205#ifdef MOTION_VECTOR_PREPASS
206    let clip_t = view.unjittered_clip_from_world * in.world_position;
207    let clip = clip_t.xy / clip_t.w;
208    let previous_clip_t = prepass_bindings::previous_view_uniforms.clip_from_world
209        * in.previous_world_position;
210    let saved_previous_clip = previous_clip_t.xy / previous_clip_t.w;
211    // Invalid history is a full temporal reset, including camera teleport.
212    let previous_clip = select(
213        clip,
214        saved_previous_clip,
215        aqua_previous_frame.valid.x >= 0.5,
216    );
217    // Bevy/Terra ABI: UV-space offset; clip Y is inverted and NDC is halved.
218    let motion = (clip - previous_clip) * vec2(0.5, -0.5);
219    // Canonical positive zero is part of the raw Rg16Float reset contract.
220    out.motion_vector = select(motion, vec2(0.0), motion == vec2(0.0));
221#endif
222    return out;
223}