Bug: PIL-based block height estimation causes severe performance degradation #38

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david · 2026-03-19T05:32:36Z

david commented

2026-03-19 05:32:36 +00:00

Bug: PIL-based block height estimation causes severe performance degradation

State: open | Author: david
Created: 2026-03-19

Problem

The ViewportFilterStage in engine/pipeline/adapters/transform.py was using estimate_block_height() which uses PIL to render blocks and measure their height. This is extremely slow and causes:

Severe performance degradation in viewport filtering
Benchmark tests to fail with coverage instrumentation
Unnecessary CPU overhead for simple height estimation

Root Cause

estimate_block_height() from engine/render/blocks.py renders each headline as a full PIL image to measure its terminal height - this is expensive and unnecessary.

Solution

Replace with simple word-wrap based estimation that:

Counts words and wraps at viewport width
Estimates 6 rows per wrapped line (big block rendering)
Is orders of magnitude faster

Fix Applied

See commit that replaces estimate_block_height with estimate_simple_height.

Part of #34 (Improve benchmarking system)
Related to #36 (CI benchmarking interference)

This bug is now fixed.

## Bug: PIL-based block height estimation causes severe performance degradation **State:** open | **Author:** david **Created:** 2026-03-19 ## Problem The `ViewportFilterStage` in `engine/pipeline/adapters/transform.py` was using `estimate_block_height()` which uses PIL to render blocks and measure their height. This is extremely slow and causes: 1. Severe performance degradation in viewport filtering 2. Benchmark tests to fail with coverage instrumentation 3. Unnecessary CPU overhead for simple height estimation ## Root Cause `estimate_block_height()` from `engine/render/blocks.py` renders each headline as a full PIL image to measure its terminal height - this is expensive and unnecessary. ## Solution Replace with simple word-wrap based estimation that: - Counts words and wraps at viewport width - Estimates 6 rows per wrapped line (big block rendering) - Is orders of magnitude faster ## Fix Applied See commit that replaces `estimate_block_height` with `estimate_simple_height`. ## Related Issues - Part of #34 (Improve benchmarking system) - Related to #36 (CI benchmarking interference) --- **This bug is now fixed.**

david closed this issue

2026-03-19 05:34:10 +00:00

david referenced this issue

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

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

david referenced this issue

2026-03-19 05:42:20 +00:00

Bug: CameraStage doesn't propagate camera_y to PipelineContext #40

david referenced this issue from a commit

2026-03-19 11:18:53 +00:00

fix(performance): use simple height estimation instead of PIL rendering

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