Tutorial: Optimizing Vector Graphics

pdfbeaver isn’t limited to one-to-one replacements. You can create Stateful Handlers that buffer multiple operators, analyze them, and write back a completely different set of instructions.

Use Case: Path Simplification

Imagine a PDF map with a coastline defined by thousands of tiny line segments. This makes the file large and slow to render. We can use the Ramer-Douglas-Peucker algorithm to simplify these lines.

Strategies for Stateful Handlers

Instead of a simple function, we can register methods of a class. This allows us to maintain a self.buffer.

  1. Intercept m (move to) and l (line to) operators. Store the points in a list.

  2. Intercept painting operators (S, f). This signals the end of a path.

  3. Process the list of points (simplify them).

  4. Flush the new, shorter list of operators to the stream.

class VectorOptimizer:
    def __init__(self):
        self.buffer = [] # Store (x, y) points

        # Create a registry just for this job
        self.registry = beaver.HandlerRegistry()

        # Register methods
        self.registry.register("m", "l")(self.handle_path)
        self.registry.register("S", "f")(self.handle_paint)

    def handle_path(self, operands, op):
        # Don't write anything yet! Just store the data.
        x, y = float(operands[0]), float(operands[1])
        self.buffer.append((x, y))
        return [] # Delete the original operator from the stream

    def handle_paint(self, operands, op):
        # The path is finished. Optimize it now.
        if len(self.buffer) > 100:
            simplified_points = self.simplify(self.buffer)

            # Reconstruct operators
            new_ops = []
            new_ops.append(([simplified_points[0]], "m"))
            for p in simplified_points[1:]:
                 new_ops.append(([p], "l"))

            # Add the paint operator at the end
            new_ops.append(([], op))

            self.buffer = []
            return new_ops

        # If path was short, just return originals (logic omitted for brevity)
        return beaver.UNCHANGED

    def simplify(self, points):
        # Implementation of Ramer-Douglas-Peucker...
        return points

# Running it
pdf = pikepdf.open("map.pdf")
optimizer = VectorOptimizer()

# Pass the custom registry
beaver.process(pdf, registry=optimizer.registry)