Vector/path tracing mode — trace actual shapes instead of raster scanlines

[parkerxhollis]

Problem

The current drawing engine uses a raster scanline approach:

• Template is a 150×N PNG
• Black pixels are drawn one-by-one in horizontal sweeps
• Every black pixel becomes an individual drag gesture

This works but has limitations:

• Lines are composed of tiny horizontal dashes (--mode tiny) or jagged row swipes (--mode strokes)
• Curves and diagonals look pixelated — like a dot matrix printer
• No concept of "draw this line from A to B" — only "fill these grid cells"
• Complex designs create thousands of drags, making drawing slow

Proposed Solution

A vector tracing mode that accepts SVG (or similar vector format) and traces the actual paths:

python draw.py logo.svg --mode vector

How it would work

1. Parse SVG paths → polylines (sequence of points)
2. Map each point to screen coordinates via the calibrated boundary
3. Trace each path with a single continuous CGEvent drag
4. Hatch fill — for filled shapes, trace the outline then fill with diagonal hatch lines

Modes within vector mode

• --mode vector-outline — trace only the outlines of shapes. Clean, sharp, fast.
• --mode vector-fill — trace outlines + fill with evenly spaced hatch lines. Gives the filled look without thousands of individual drags.
• --mode vector-hatch — fill shapes with parallel lines at configurable angle/spacing (--hatch-angle 45 --hatch-spacing 8)

Benefits

• Sharper — continuous drags along actual curves, not stair-stepped approximations
• Faster — a circle is 1 stroke instead of hundreds of pixel drags
• Smaller input — SVG files are tiny compared to 150×N PNGs
• Fill support — hatching gives the illusion of filled areas without needing every pixel
• Portable — same SVG works for both RevoDraw and CashDraw once implemented

Implementation Sketch

def extract_vector_paths(svg_path: str, boundary: dict, cols: int, rows: int):
    """Parse SVG, return list of screen-coordinate polylines."""
    # Use svg.path or similar library
    # Convert bezier curves to polyline approximations
    # Map to screen coords
    return paths  # list of [(x1,y1), (x2,y2), ...]

def draw_vector_paths(paths, mode="outline", hatch_spacing=8, hatch_angle=45):
    """Trace each path with CGEvent drag."""
    for path in paths:
        for i in range(len(path) - 1):
            cg_drag(path[i][0], path[i][1], path[i+1][0], path[i+1][1])
    if mode == "fill":
        # generate and trace hatch lines
        ...

Prior Art

• vpype — Python vector processing for plotters
• svg.path — SVG path parsing
• Plotter-like hatching algorithms (widely documented)

Dependencies to evaluate

• svg.path or svgpathtools — path parsing
• shapely — polygon operations for hatch fill
• Or keep it simple: require pre-processed polylines in a JSON format

Once proven on RevoDraw

Port the vector engine to cashapp-draw-ios.