chart-image

# Chart Image Generator Generate PNG chart images from data using Vega-Lite. Perfect for headless server environments. ## Why This Skill? **Built for Fly.io / VPS / Docker deployments:** - ✅ **No native compilation** - Uses Sharp with prebuilt binaries (unlike `canvas` which requires build tools) - ✅ **No Puppeteer/browser** - Pure Node.js, no Chrome download, no headless browser overhead - ✅ **Lightweight** - ~15MB total dependencies vs 400MB+ for Puppeteer-based solutions - ✅ **Fast cold starts** - No browser spinup delay, generates charts in <500ms - ✅ **Works offline** - No external API calls (unlike QuickChart.io) ## Setup (one-time) ```bash cd /data/clawd/skills/chart-image/scripts && npm install ``` ## Quick Usage ```bash node /data/clawd/skills/chart-image/scripts/chart.mjs \ --type line \ --data '[{"x":"10:00","y":25},{"x":"10:30","y":27},{"x":"11:00","y":31}]' \ --title "Price Over Time" \ --output chart.png ``` ## Chart Types ### Line Chart (default) ```bash node chart.mjs --type line --data '[{"x":"A","y":10},{"x":"B","y":15}]' --output line.png ``` ### Bar Chart ```bash node chart.mjs --type bar --data '[{"x":"A","y":10},{"x":"B","y":15}]' --output bar.png ``` ### Area Chart ```bash node chart.mjs --type area --data '[{"x":"A","y":10},{"x":"B","y":15}]' --output area.png ``` ### Pie / Donut Chart ```bash # Pie node chart.mjs --type pie --data '[{"category":"A","value":30},{"category":"B","value":70}]' \ --category-field category --y-field value --output pie.png # Donut (with hole) node chart.mjs --type donut --data '[{"category":"A","value":30},{"category":"B","value":70}]' \ --category-field category --y-field value --output donut.png ``` ### Candlestick Chart (OHLC) ```bash node chart.mjs --type candlestick \ --data '[{"x":"Mon","open":100,"high":110,"low":95,"close":105}]' \ --open-field open --high-field high --low-field low --close-field close \ --title "Stock Price" --output candle.png ``` ### Heatmap ```bash node chart.mjs --type heatmap \ --data '[{"x":"Mon","y":"Week1","value":5},{"x":"Tue","y":"Week1","value":8}]' \ --color-value-field value --color-scheme viridis \ --title "Activity Heatmap" --output heatmap.png ``` ### Multi-Series Line Chart Compare multiple trends on one chart: ```bash node chart.mjs --type line --series-field "market" \ --data '[{"x":"Jan","y":10,"market":"A"},{"x":"Jan","y":15,"market":"B"}]' \ --title "Comparison" --output multi.png ``` ### Stacked Bar Chart ```bash node chart.mjs --type bar --stacked --color-field "category" \ --data '[{"x":"Mon","y":10,"category":"Work"},{"x":"Mon","y":5,"category":"Personal"}]' \ --title "Hours by Category" --output stacked.png ``` ### Volume Overlay (Dual Y-axis) Price line with volume bars: ```bash node chart.mjs --type line --volume-field volume \ --data '[{"x":"10:00","y":100,"volume":5000},{"x":"11:00","y":105,"volume":3000}]' \ --title "Price + Volume" --output volume.png ``` ### Sparkline (mini inline chart) ```bash node chart.mjs --sparkline --data '[{"x":"1","y":10},{"x":"2","y":15}]' --output spark.png ``` Sparklines are 80x20 by default, transparent, no axes. ## Options Reference ### Basic Options | Option | Description | Default | |--------|-------------|---------| | `--type` | Chart type: line, bar, area, point, pie, donut, candlestick, heatmap | line | | `--data` | JSON array of data points | - | | `--output` | Output file path | chart.png | | `--title` | Chart title | - | | `--width` | Width in pixels | 600 | | `--height` | Height in pixels | 300 | ### Axis Options | Option | Description | Default | |--------|-------------|---------| | `--x-field` | Field name for X axis | x | | `--y-field` | Field name for Y axis | y | | `--x-title` | X axis label | field name | | `--y-title` | Y axis label | field name | | `--x-type` | X axis type: ordinal, temporal, quantitative | ordinal | | `--y-domain` | Y scale as "min,max" | auto | ### Visual Options | Option | Description | Default | |--------|-------------|---------| | `--color` | Line/bar color | #e63946 | | `--dark` | Dark mode theme | false | | `--svg` | Output SVG instead of PNG | false | | `--color-scheme` | Vega color scheme (category10, viridis, etc.) | - | ### Alert/Monitor Options | Option | Description | Default | |--------|-------------|---------| | `--show-change` | Show +/-% change annotation at last point | false | | `--focus-change` | Zoom Y-axis to 2x data range | false | | `--focus-recent N` | Show only last N data points | all | | `--show-values` | Label min/max peak points | false | ### Multi-Series/Stacked Options | Option | Description | Default | |--------|-------------|---------| | `--series-field` | Field for multi-series line charts | - | | `--stacked` | Enable stacked bar mode | false | | `--color-field` | Field for stack/color categories | - | ### Candlestick Options | Option | Description | Default | |--------|-------------|---------| | `--open-field` | OHLC open field | open | | `--high-field` | OHLC high field | high | | `--low-field` | OHLC low field | low | | `--close-field` | OHLC close field | close | ### Pie/Donut Options | Option | Description | Default | |--------|-------------|---------| | `--category-field` | Field for pie slice categories | x | | `--donut` | Render as donut (with center hole) | false | ### Heatmap Options | Option | Description | Default | |--------|-------------|---------| | `--color-value-field` | Field for heatmap intensity | value | | `--y-category-field` | Y axis category field | y | ### Dual-Axis Options (General) | Option | Description | Default | |--------|-------------|---------| | `--y2-field` | Second Y axis field (independent right axis) | - | | `--y2-title` | Title for second Y axis | field name | | `--y2-color` | Color for second series | #60a5fa (dark) / #2563eb (light) | | `--y2-type` | Chart type for second axis: line, bar, area | line | **Example:** Revenue bars (left) + Churn area (right): ```bash node chart.mjs \ --data '[{"month":"Jan","revenue":12000,"churn":4.2},...]' \ --x-field month --y-field revenue --type bar \ --y2-field churn --y2-type area --y2-color "#60a5fa" \ --y-title "Revenue ($)" --y2-title "Churn (%)" \ --x-sort none --dark --title "Revenue vs Churn" ``` ### Volume Overlay Options (Candlestick) | Option | Description | Default | |--------|-------------|---------| | `--volume-field` | Field for volume bars (enables dual-axis) | - | | `--volume-color` | Color for volume bars | #4a5568 | ### Formatting Options | Option | Description | Default | |--------|-------------|---------| | `--y-format` | Y axis format: percent, dollar, compact, decimal4, integer, scientific, or d3-format string | auto | | `--subtitle` | Subtitle text below chart title | - | | `--hline` | Horizontal reference line: "value" or "value,color" or "value,color,label" (repeatable) | - | ### Annotation Options | Option | Description | Default |