MagickWand: significant performance drop when stroking paths with scale > 1

ImageMagick version

7.1.1-46

Operating system

Linux

Operating system, version and so on

Ubuntu 22.04 LTS

Description

We encountered some very strange behavior when drawing geometries.

Here is an example of what we want to draw (50_000 circles):

This works satisfactorily fast (about 4 seconds) in three out of four cases. But when the circle has a stroke and the scaling in the transformation is greater than one, there is a sharp drop in performance—drawing takes 44 seconds.

The situation is even worse if the circle is drawn using a path (arc with angle=2*PI). In this case, drawing 50,000 circles will not complete.

Steps to Reproduce

These images are automatically generated by our library. The MVG is dumped using the DrawGetVectorGraphics function.

DrawCircle test:

1. Unzip circle_50000.zip
2. Run magick -size 600x400 mvg:./circle_50000.mvg circle_50000.png
   Result: conversion takes acceptable time, like ~5 seconds (could be better, though?)
3. Unzip circle_50000@2x.zip
4. Run magick -size 1200x800 mvg:./circle_50000@2x.mvg circle_50000@2x.png
   Result: conversion takes unacceptable 40+ seconds, yet the only difference is the affine 2 0 0 2 0 0 at the beginning of the file.

DrawPath* test:

1. Unzip path_10000.zip
2. Run magick -size 800x400 mvg:./path_10000.mvg path_10000.png
   Result: converted in zero seconds.
3. Unzip path_10000@2x.zip
4. Run magick -size 1200x800 mvg:./path_10000@2x.mvg path_10000@2x.png
   Result: conversion takes unacceptable 5 seconds to draw just 10_000 circles, yet the only difference is the affine 2 0 0 2 0 0 at the beginning of the file.

Images

circle_50000.zip
circle_50000@2x.zip
path_10000.zip
path_10000@2x.zip

Reproduce the slowdown with the supplied circle_50000, circle_50000@2x, path_10000, and path_10000@2x MVG archives using the documented magick commands. Start by comparing rendering with and without the affine scale and trace the MagickWand drawing path handling. Done means scaled stroked circles and paths render without the reported severe performance regression, with benchmarks covering both cases.