Improve screenshot capture performance (0.7.1) - #37

packages/tugboat/lib/src/screenshot_capturer.dart:467

• Updating _lastDHash for every result makes the new tolerance drift: if stored frame H0 is reused for H1 at distance 2, state advances to H1, so H2 can be distance 2 from H1 but 4 from the still-reused H0 and also be skipped; repeated changes can diverge arbitrarily. This also commits hashes from attempts later discarded as stale. Compare against and commit only the hash of an actually accepted/stored frame.

        if (encoded.dHash != null) {
          _lastDHash = encoded.dHash;

packages/tugboat/lib/src/screenshot_encode.dart:95

• computeDHashFromRgba samples only one source pixel for each of the 72 hash cells (perceptual_hash.dart:13-22). The removed path first rendered the full screenshot down to a filtered 9×8 thumbnail; calling this helper directly on a viewport makes changes away from those sample points invisible, so meaningful text or control updates can be coalesced. Downsample/aggregate the full image to 9×8 in the worker before comparing adjacent pixels.

  final dHash = computeDHashFromRgba(rgba, input.width, input.height);

packages/tugboat/lib/src/controller.dart:2180

• Coalescing is still allowed when this request has no compatible frame. In that case either the paint-generation gate or dHash can return an empty result, _reuseWithoutCapture/the dHash branch returns noCompatibleFrame, and unchanged subsequent requests repeat the same skip instead of ever creating usable evidence (for example after a boundary-transform generation change). Bypass coalescing whenever _compatibleFrameFor(context) is null.

        force: force || requiresFreshPaint,

packages/tugboat/lib/src/screenshot_capturer.dart:475

• Do not advance the dHash baseline before the controller accepts or successfully reuses this result. captureAttempt can discard the result after encoding when its route/session becomes stale, and dHash coalescing can also return no compatible frame; the next attempt can then coalesce against an unaccepted image, return empty bytes, and again produce no frame. Commit the dHash alongside the paint signature only after acceptance/reuse.

            height: imageHeight,
            maskRects: scaledMasks,

packages/tugboat/lib/src/capture_boundary.dart:52

• This signature misses compositing-only visual updates. Retained layers such as OpacityLayer, TransformLayer, and OffsetLayer can mutate alpha/transform/offset in place while both the layer and PictureLayer.picture identities remain unchanged, so the gate can reuse a stale screenshot even though the rendered pixels changed. Track the relevant layer state or a generation that also advances for composited-layer updates before using equality as a no-readback proof.

    signature = Object.hash(signature, identityHashCode(layer));
    if (layer is PictureLayer) {
      signature = Object.hash(signature, identityHashCode(layer.picture));
    }

packages/tugboat/lib/src/controller.dart:2236

• A paint-signature match does not guarantee that a compatible frame exists. For example, _captureContext advances boundaryTransformGeneration when the boundary moves, while the retained boundary pixels/signature may remain unchanged; this branch then calls _reuseWithoutCapture, gets noCompatibleFrame, and never retries the capture. Only enable the gate when a compatible frame is known, or retry without the gate when reuse fails.

        );
      }
      _lastCaptureFailure = null;

      if (result.skippedByPaintGeneration) {

packages/tugboat/pubspec.yaml:4

• The release bump leaves the repository's release documentation inconsistent: docs/README.md:31, docs/integration/production-replay-acceptance.md:15, and docs/integration/production-replay-acceptance.md:167 still identify 0.7.0 as current/under test. Update those references as part of the 0.7.1 release.

version: 0.7.1