Tweakpane Visual Debugger

Overview

Debug visual CSS and layout issues in the tweakpane-table plugin using Playwright browser automation. Measure actual element dimensions, compare DOM structures, inspect CSS properties, and identify root causes of alignment problems between table headers and data cells.

When to Use This Skill

Use this skill in these scenarios:

• Columns don't align between headers and data rows
• CSS changes don't produce expected visual results
• Need to verify actual rendered dimensions vs expected
• Investigating why width properties aren't being applied
• Comparing CSS properties between headers and rows
• User reports "still looks the same" after fixes

Debugging Workflow

Step 1: Navigate to Test Page

Open the local test HTML file in the Playwright browser.

Available test files:

• test/simple.html - Basic 2-column table (Text, List)
• test/advanced.html - Complex 5-column table (Name, Type, Link, Trigger, Delete)

Navigate using absolute path:

Use mcp__playwright__browser_navigate

Construct the absolute path from the working directory (/data/Workspace/helios/tweakpane-table):

file:///data/Workspace/helios/tweakpane-table/test/simple.html

Step 2: Capture Visual State

After navigation, capture both accessibility and visual information:

1. Take accessibility snapshot:

   Use mcp__playwright__browser_snapshot
   

   This provides the DOM structure in a text format.

2. Take visual screenshot:

   Use mcp__playwright__browser_take_screenshot
   

   Set fullPage: false for viewport screenshot, or fullPage: true for entire page. Save as: alignment-issue-{timestamp}.png

Step 3: Measure Table Elements

Run the comprehensive measurement script to get precise dimensions and CSS properties.

Execute measure_table.js:

Use mcp__playwright__browser_evaluate

function: Read scripts/measure_table.js file content and pass as the function parameter

Script returns:

• Header cell dimensions and positions
• Row cell dimensions and positions
• CSS properties (flex, width, padding, margin, etc.)
• Inline styles applied
• Alignment differences calculated automatically

Analyze the results for:

• Width differences between header and row cells in same column
• Different flex-basis values
• Different padding/margin
• Missing inline styles (width not applied)

Step 4: Compare DOM Structure

Run the structure comparison script to identify hierarchy differences.

Execute compare_structure.js:

Use mcp__playwright__browser_evaluate

function: Read scripts/compare_structure.js file content and pass as the function parameter

Script returns:

• Full DOM hierarchy for headers and rows
• Path to cells comparison
• Structural differences
• Tag/class mismatches
• CSS property differences at each level

Look for:

• Different nesting depths
• Extra wrapper elements in headers vs rows
• Different element types (buttons vs inputs)
• Class name differences

Step 5: Inspect Specific Elements

If measurement scripts reveal issues, inspect specific elements interactively.

Check inline styles:

() => {
  const headerCell = document.querySelector('.tp-headv .tp-lblv');
  const rowCell = document.querySelector('.tp-rowv .tp-lblv');

  return {
    header: {
      inlineWidth: headerCell.style.width,
      inlineFlex: headerCell.style.flex,
      allInlineStyles: headerCell.style.cssText
    },
    row: {
      inlineWidth: rowCell.style.width,
      inlineFlex: rowCell.style.flex,
      allInlineStyles: rowCell.style.cssText
    }
  };
}

Check computed styles:

() => {
  const headerCell = document.querySelector('.tp-headv .tp-lblv');
  const rowCell = document.querySelector('.tp-rowv .tp-lblv');
  const hcs = window.getComputedStyle(headerCell);
  const rcs = window.getComputedStyle(rowCell);

  return {
    header: {
      width: hcs.width,
      flex: hcs.flex,
      flexBasis: hcs.flexBasis,
      flexGrow: hcs.flexGrow,
      flexShrink: hcs.flexShrink,
      minWidth: hcs.minWidth,
      maxWidth: hcs.maxWidth,
      padding: hcs.padding,
      boxSizing: hcs.boxSizing
    },
    row: {
      width: rcs.width,
      flex: rcs.flex,
      flexBasis: rcs.flexBasis,
      flexGrow: rcs.flexGrow,
      flexShrink: rcs.flexShrink,
      minWidth: rcs.minWidth,
      maxWidth: rcs.maxWidth,
      padding: rcs.padding,
      boxSizing: rcs.boxSizing
    }
  };
}

Step 6: Identify Root Cause

Based on measurements and comparisons, identify the root cause:

Common issues to check:

1. Width not applied

   • Check if inline width or flex exists on cells
   • Verify width is applied to correct element (.tp-lblv not .tp-lblv_v)

2. Flex properties overriding width

   • Check if flex: 1 on child .tp-lblv_v causes expansion
   • Verify flex-grow: 0 and flex-shrink: 0 are set
   • Should use flex: 0 0 {width} not just width

3. Structural differences

   • Different nesting levels between headers and rows
   • Different element types (buttons vs inputs)
   • Extra wrappers in one but not the other

4. Padding/margin differences

   • Different padding on header vs row cells
   • Different margin causing spacing issues

5. Label visibility

   • Labels visible in headers but hidden in rows
   • Creates extra width in headers

Step 7: Reference Documentation

For deeper understanding, read the reference documentation:

Tweakpane DOM structure:

Read references/tweakpane-dom-structure.md

Explains:

• Core Tweakpane classes (.tp-lblv, .tp-brkv, .tp-rotv)
• Tweakpane-table plugin structure
• Where width should be applied
• Why flex is needed instead of width

Common alignment issues:

Read references/common-alignment-issues.md

Catalogs known issues:

• Headers wider than data cells
• Labels visible in wrong places
• Different padding
• Box-sizing mismatches
• Flex direction problems
• Min-width constraints

Step 8: Report Findings

Structure the debugging report:

## Visual Alignment Issue Analysis

### 1. Visual Evidence
[Screenshot showing the alignment issue]

### 2. Measurements
[Table showing header vs row widths for each column]

Column | Header Width | Row Width | Difference | Aligned?
-------|-------------|-----------|------------|----------
0      | 123.5px     | 98.2px    | 25.3px     | ❌
1      | 245.0px     | 245.0px   | 0px        | ✅

### 3. Root Cause
[Explanation of what's wrong]

Example: "Width is being set as inline `width` property, but the child `.tp-lblv_v` element has `flex: 1` which causes it to expand beyond the parent's width constraint."

### 4. CSS/DOM Differences
[List of specific differences between headers and rows]

### 5. Recommended Fix
[Specific code changes with file names and line numbers]

Example:
```javascript
// In src/head.ts line 126:
// Change from:
api.element.style.width = headerParams.width;

// To:
api.element.style.flex = `0 0 ${headerParams.width}`;

6. Verification Steps

[How to verify the fix works]

## Key Files Reference

When implementing fixes, check these files:

- `src/sass/plugin.scss` - CSS styles for table layout
- `src/head.ts` - Header implementation (line ~126: width application)
- `src/row.ts` - Row implementation (line ~112: RowPane.addBinding width application)
- `test/simple.html` - Basic test case
- `test/advanced.html` - Complex test case

## Testing After Fixes

1. Apply the recommended fix
2. Rebuild the plugin: `npm run build:dev`
3. Reload the test page in browser (hard refresh: Ctrl+Shift+R)
4. Re-run measurement scripts to verify alignment
5. Test both simple.html and advanced.html
6. Take new screenshots to confirm fix

## Resources

### scripts/

**measure_table.js** - Comprehensive measurement script that:
- Measures all header and row cell dimensions
- Captures CSS properties (computed and inline)
- Calculates alignment differences automatically
- Returns structured data for analysis

**compare_structure.js** - DOM structure comparison script that:
- Builds hierarchical tree of elements
- Compares header vs row structure
- Identifies tag/class/CSS mismatches
- Reports differences at each nesting level

### references/

**tweakpane-dom-structure.md** - Complete reference for:
- Tweakpane v4 DOM structure
- Core classes and their purposes
- Tweakpane-table plugin structure
- Width application requirements
- Common CSS rules

**common-alignment-issues.md** - Catalog of known issues:
- Issue symptoms and root causes
- Diagnostic procedures
- Solutions with code examples
- Prevention checklist