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| 1 | +//! Dirty-range planning for the renderer's large lighting uniform buffer. |
| 2 | +//! |
| 3 | +//! Lighting setters mutate the CPU snapshot throughout a frame. Uploading the |
| 4 | +//! complete ~9 KiB block after every setter made one ordinary frame enqueue the |
| 5 | +//! same data many times. This tracker compares the final snapshot against the |
| 6 | +//! last submitted bytes and emits at most one aligned range for each logical |
| 7 | +//! region: fixed/directional fields, point lights, and view/shadow/frame data. |
| 8 | +
|
| 9 | +use std::ops::Range; |
| 10 | + |
| 11 | +use super::types::LightingUniforms; |
| 12 | + |
| 13 | +const POINT_LIGHTS_OFFSET: usize = std::mem::offset_of!(LightingUniforms, point_lights); |
| 14 | +const VIEW_DATA_OFFSET: usize = std::mem::offset_of!(LightingUniforms, camera_pos); |
| 15 | +const LIGHTING_BYTES: usize = std::mem::size_of::<LightingUniforms>(); |
| 16 | +const REGIONS: [Range<usize>; 3] = [ |
| 17 | + 0..POINT_LIGHTS_OFFSET, |
| 18 | + POINT_LIGHTS_OFFSET..VIEW_DATA_OFFSET, |
| 19 | + VIEW_DATA_OFFSET..LIGHTING_BYTES, |
| 20 | +]; |
| 21 | + |
| 22 | +#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)] |
| 23 | +pub(super) struct LightingUploadStats { |
| 24 | + pub(super) write_count: u32, |
| 25 | + pub(super) byte_count: u64, |
| 26 | +} |
| 27 | + |
| 28 | +pub(super) struct LightingUploadBatch { |
| 29 | + ranges: [Option<Range<usize>>; 3], |
| 30 | +} |
| 31 | + |
| 32 | +impl LightingUploadBatch { |
| 33 | + pub(super) fn ranges(&self) -> impl Iterator<Item = &Range<usize>> { |
| 34 | + self.ranges.iter().flatten() |
| 35 | + } |
| 36 | +} |
| 37 | + |
| 38 | +pub(super) struct LightingUploadTracker { |
| 39 | + last_uploaded: LightingUniforms, |
| 40 | + frame_stats: LightingUploadStats, |
| 41 | +} |
| 42 | + |
| 43 | +impl LightingUploadTracker { |
| 44 | + pub(super) fn new(initial: LightingUniforms) -> Self { |
| 45 | + Self { |
| 46 | + last_uploaded: initial, |
| 47 | + frame_stats: LightingUploadStats::default(), |
| 48 | + } |
| 49 | + } |
| 50 | + |
| 51 | + pub(super) fn begin_frame(&mut self) { |
| 52 | + self.frame_stats = LightingUploadStats::default(); |
| 53 | + } |
| 54 | + |
| 55 | + pub(super) fn plan(&mut self, current: LightingUniforms) -> LightingUploadBatch { |
| 56 | + let current_bytes = bytemuck::bytes_of(¤t); |
| 57 | + let previous_bytes = bytemuck::bytes_of(&self.last_uploaded); |
| 58 | + let ranges = REGIONS |
| 59 | + .clone() |
| 60 | + .map(|region| changed_word_range(current_bytes, previous_bytes, region)); |
| 61 | + for range in ranges.iter().flatten() { |
| 62 | + self.frame_stats.write_count = self.frame_stats.write_count.saturating_add(1); |
| 63 | + self.frame_stats.byte_count = self |
| 64 | + .frame_stats |
| 65 | + .byte_count |
| 66 | + .saturating_add((range.end - range.start) as u64); |
| 67 | + } |
| 68 | + self.last_uploaded = current; |
| 69 | + LightingUploadBatch { ranges } |
| 70 | + } |
| 71 | + |
| 72 | + #[cfg(not(target_arch = "wasm32"))] |
| 73 | + pub(super) fn frame_stats(&self) -> LightingUploadStats { |
| 74 | + self.frame_stats |
| 75 | + } |
| 76 | +} |
| 77 | + |
| 78 | +fn changed_word_range( |
| 79 | + current: &[u8], |
| 80 | + previous: &[u8], |
| 81 | + region: Range<usize>, |
| 82 | +) -> Option<Range<usize>> { |
| 83 | + debug_assert_eq!(region.start % wgpu::COPY_BUFFER_ALIGNMENT as usize, 0); |
| 84 | + debug_assert_eq!(region.end % wgpu::COPY_BUFFER_ALIGNMENT as usize, 0); |
| 85 | + let alignment = wgpu::COPY_BUFFER_ALIGNMENT as usize; |
| 86 | + let first = (region.start..region.end) |
| 87 | + .step_by(alignment) |
| 88 | + .find(|&offset| { |
| 89 | + current[offset..offset + alignment] != previous[offset..offset + alignment] |
| 90 | + })?; |
| 91 | + let last = (region.start..region.end) |
| 92 | + .step_by(alignment) |
| 93 | + .rev() |
| 94 | + .find(|&offset| current[offset..offset + alignment] != previous[offset..offset + alignment]) |
| 95 | + .expect("the first changed word proves a last changed word exists"); |
| 96 | + Some(first..last + alignment) |
| 97 | +} |
| 98 | + |
| 99 | +#[cfg(test)] |
| 100 | +mod tests { |
| 101 | + use super::{LightingUploadTracker, LIGHTING_BYTES}; |
| 102 | + use crate::renderer::types::LightingUniforms; |
| 103 | + |
| 104 | + #[test] |
| 105 | + fn unchanged_snapshot_schedules_no_upload() { |
| 106 | + let lighting = LightingUniforms::defaults(); |
| 107 | + let mut tracker = LightingUploadTracker::new(lighting); |
| 108 | + tracker.begin_frame(); |
| 109 | + |
| 110 | + assert_eq!(tracker.plan(lighting).ranges().count(), 0); |
| 111 | + assert_eq!(tracker.frame_stats().write_count, 0); |
| 112 | + assert_eq!(tracker.frame_stats().byte_count, 0); |
| 113 | + } |
| 114 | + |
| 115 | + #[test] |
| 116 | + fn changes_are_bounded_to_three_non_overlapping_regions() { |
| 117 | + let initial = LightingUniforms::defaults(); |
| 118 | + let mut changed = initial; |
| 119 | + changed.ambient[0] = 0.25; |
| 120 | + changed.point_lights[7].position[2] = 42.0; |
| 121 | + changed.camera_pos[0] = 3.0; |
| 122 | + |
| 123 | + let mut tracker = LightingUploadTracker::new(initial); |
| 124 | + tracker.begin_frame(); |
| 125 | + let batch = tracker.plan(changed); |
| 126 | + let ranges: Vec<_> = batch.ranges().cloned().collect(); |
| 127 | + |
| 128 | + assert_eq!(ranges.len(), 3); |
| 129 | + assert!(ranges.windows(2).all(|pair| pair[0].end <= pair[1].start)); |
| 130 | + assert_eq!(tracker.frame_stats().write_count, 3); |
| 131 | + assert!(tracker.frame_stats().byte_count < LIGHTING_BYTES as u64); |
| 132 | + } |
| 133 | + |
| 134 | + #[test] |
| 135 | + fn repeated_setter_mutations_coalesce_before_planning() { |
| 136 | + let initial = LightingUniforms::defaults(); |
| 137 | + let mut changed = initial; |
| 138 | + changed.point_lights[3].position = [1.0, 2.0, 3.0, 4.0]; |
| 139 | + changed.point_lights[3].color = [0.2, 0.4, 0.6, 8.0]; |
| 140 | + |
| 141 | + let mut tracker = LightingUploadTracker::new(initial); |
| 142 | + tracker.begin_frame(); |
| 143 | + let batch = tracker.plan(changed); |
| 144 | + |
| 145 | + assert_eq!(batch.ranges().count(), 1); |
| 146 | + assert_eq!(tracker.frame_stats().write_count, 1); |
| 147 | + assert_eq!(tracker.frame_stats().byte_count, 32); |
| 148 | + } |
| 149 | +} |
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