Representation¶

Overview¶

SketchKit uses a unified representation for sketches, making it easy to work with various datasets.
All sketches are converted into the Sketch standard format, which provides a structured way to access paths, curves and points.

Architecture Overview¶

A Sketch is composed of several levels of hierarchy, which contains a list of Paths.
A Path contains a list of Curves.
And each Curve is a cubic bezier curve with start and end vertices and two control points.
A Vertex is a point with many other drawing attributes than naive Point (which only has x,y position).

The structure can be visualized as follows:

Sketch
  - Path
    - Curve
      - Start Vertex
      - End Vertex
      - Control Point 1
      - Control Point 2
    - Curve
    ...
  - Path
  ...

Core Components¶

Sketch¶

The top-level object representing a full sketch.
Contains multiple paths.

Path¶

A sequence of one or more curves that form a continuous stroke.
e.g. A single hand-drawn line

Curve¶

A cubic Bézier curve connecting two vertices.
e.g. cutting a path into multiple parts, each part represents a curve
Defined by:
- Start Vertex
- End Vertex
- Control Point 1
- Control Point 2

Vertex¶

A specialized point with additional drawing attributes.
Attributes include:
- pressure: pen pressure at this point
- thickness: stroke width at this point
- Other style information
e.g. every curve’s start and end points are vertices.

Point¶

The most basic element in a sketch.
Stores the 2D position (x, y) of a point.
e.g. mostly serve as control points for cubic Bézier curves, defining the curve’s shape.

Example¶

Here’s a example to demonstrate how to explore SketchKit’s representation:

from sketchkit.datasets import QuickDraw
from sketchkit.renderer.cairo_renderer import CairoRenderer
from PIL import Image

# Load a dataset and get a sketch
print("Loading QuickDraw dataset...")
dataset = QuickDraw()
sketch = dataset[0]

print("=== Sketch Overview ===")
print(f"Dataset: {type(dataset).__name__}")
print(f"Sketch has {sketch.path_num} paths")
print(f"Total curves: {sketch.curve_num}")

# Analyze each path
print("\n=== Path Analysis ===")
for i, path in enumerate(sketch.paths):
    print(f"Path {i}:")
    print(f"  - Curves: {len(path.curves)}")
    
    # Look at first curve in detail
    if path.curves:
        first_curve = path.curves[0]
        print(f"  - First curve start: ({first_curve.p_start.x:.1f}, {first_curve.p_start.y:.1f})")
        print(f"  - First curve end: ({first_curve.p_end.x:.1f}, {first_curve.p_end.y:.1f})")
        
        # Check for pressure information
        if first_curve.p_start.pressure is not None:
            print(f"  - Start pressure: {first_curve.p_start.pressure:.2f}")
        else:
            print("  - No pressure information available")

# Calculate some statistics
print("\n=== Statistics ===")
total_vertices = 0
all_x_coords = []
all_y_coords = []

for path in sketch.paths:
    for curve in path.curves:
        total_vertices += 2  # start and end vertex
        all_x_coords.extend([curve.p_start.x, curve.p_end.x])
        all_y_coords.extend([curve.p_start.y, curve.p_end.y])

if all_x_coords:
    print(f"Total vertices: {total_vertices}")
    print(f"X range: {min(all_x_coords):.1f} to {max(all_x_coords):.1f}")
    print(f"Y range: {min(all_y_coords):.1f} to {max(all_y_coords):.1f}")

# Render the sketch
print("\n=== Rendering ===")
renderer = CairoRenderer(canvas_size=400, canvas_color=(1, 1, 1))
image = renderer.render(sketch)
output_path = "example_sketch.png"
Image.fromarray(image, "RGB").save(output_path)
print(f"Sketch rendered and saved to {output_path}")