Bug: Camera update() method never called, scroll position never advances #39

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david · 2026-03-19T05:42:16Z

david commented

2026-03-19 05:42:16 +00:00

Problem

The camera's update(dt) method is never called in the pipeline execution loop, causing the scroll camera position to remain static at 0.

Root Cause

No dt calculation in main loop: The frame loop in engine/app/pipeline_runner.py sleeps for 1/60 second but never calculates delta time
No camera.update() call: The Camera class has update() method for advancing position, but it's never invoked
CameraStage isolation: CameraStage only calls camera.apply() to slice the buffer, never advances camera position

Expected Behavior

With --pipeline-camera scroll, the viewport should smoothly scroll upward at a configured speed, showing different parts of the content over time.

Current Behavior

Viewport remains static at position 0, no scrolling motion occurs.

Code Locations

engine/camera.py: Camera class has update(dt) method (line 122) and _update_scroll() (line 171)
engine/app/pipeline_runner.py: Main loop (line 643-691) lacks dt tracking and camera.update() call
engine/pipeline/adapters/camera.py: CameraStage.process() calls camera.apply() but never camera.update()

Proposed Fix

Following Option 1 (CameraStage self-contained):

Calculate dt in CameraStage using frame timing
Call camera.update(dt) in CameraStage.process()
This keeps camera logic self-contained

Issue #38: Already fixed - PIL height estimation performance fix
Issue #35: Pipeline Mutation API - camera hot-swap capability

Acceptance Criteria

Scroll camera position advances each frame
ViewportFilterStage reads correct camera_y from context
Smooth vertical scrolling visible in terminal output

## Problem The camera's `update(dt)` method is never called in the pipeline execution loop, causing the scroll camera position to remain static at 0. ## Root Cause 1. **No dt calculation in main loop**: The frame loop in `engine/app/pipeline_runner.py` sleeps for 1/60 second but never calculates delta time 2. **No camera.update() call**: The Camera class has `update()` method for advancing position, but it's never invoked 3. **CameraStage isolation**: CameraStage only calls `camera.apply()` to slice the buffer, never advances camera position ## Expected Behavior With `--pipeline-camera scroll`, the viewport should smoothly scroll upward at a configured speed, showing different parts of the content over time. ## Current Behavior Viewport remains static at position 0, no scrolling motion occurs. ## Code Locations - `engine/camera.py`: Camera class has `update(dt)` method (line 122) and `_update_scroll()` (line 171) - `engine/app/pipeline_runner.py`: Main loop (line 643-691) lacks dt tracking and camera.update() call - `engine/pipeline/adapters/camera.py`: CameraStage.process() calls `camera.apply()` but never `camera.update()` ## Proposed Fix Following Option 1 (CameraStage self-contained): - Calculate dt in CameraStage using frame timing - Call `camera.update(dt)` in CameraStage.process() - This keeps camera logic self-contained ## Related Issues - Issue #38: Already fixed - PIL height estimation performance fix - Issue #35: Pipeline Mutation API - camera hot-swap capability ## Acceptance Criteria - [ ] Scroll camera position advances each frame - [ ] ViewportFilterStage reads correct camera_y from context - [ ] Smooth vertical scrolling visible in terminal output

david referenced this issue

2026-03-19 05:42:26 +00:00

Epic: Pipeline Mutation API for Stage Hot-Swapping #35

david commented

2026-03-19 05:42:32 +00:00

Summary

Created two linked bug tickets that together cause scroll camera motion to fail:

#39 - Camera update never called:

camera.update(dt) never called in main loop
Camera position never advances

#40 - Camera state not propagated:

CameraStage doesn't set camera_y in context
ViewportFilterStage can't filter based on camera position

Root Cause Analysis

The CameraStage adapter only applies camera slicing to the buffer:

return self._camera.apply(data, viewport_width, viewport_height)

But the Camera class also needs:

update(dt) called each frame to advance position
camera.y propagated to context for dependent stages

Fix Strategy

Following your choice of Option 1 (CameraStage self-contained):

Calculate dt in CameraStage.process()
Call camera.update(dt)
Set ctx.set_state("camera_y", camera.y)

This keeps camera logic self-contained and requires minimal changes to main loop.

## Summary Created two linked bug tickets that together cause scroll camera motion to fail: **#39** - Camera update never called: - `camera.update(dt)` never called in main loop - Camera position never advances **#40** - Camera state not propagated: - `CameraStage` doesn't set `camera_y` in context - `ViewportFilterStage` can't filter based on camera position ## Root Cause Analysis The `CameraStage` adapter only applies camera slicing to the buffer: ```python return self._camera.apply(data, viewport_width, viewport_height) ``` But the Camera class also needs: 1. `update(dt)` called each frame to advance position 2. `camera.y` propagated to context for dependent stages ## Fix Strategy Following your choice of **Option 1 (CameraStage self-contained)**: - Calculate dt in CameraStage.process() - Call camera.update(dt) - Set ctx.set_state("camera_y", camera.y) This keeps camera logic self-contained and requires minimal changes to main loop.

david closed this issue

2026-03-19 05:46:58 +00:00

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Reference: klubhaus/sideline#39