Extremely slow editing performance

Nobody has claimed this yet.

## Description

The app has a very slow editing performance, to the point that it's unusable on my laptop with Intel i5-8250U, as shown in my screen recording below:

https://user-images.githubusercontent.com/1403194/168755176-b39aada6-55f7-437f-82ce-775652dd3a13.mp4

From my observation, it seems that the app doesn't utilize hardware acceleration (GPU processing) at all as seen in the `intel_gpu_top`.

For a demonstration purpose, I compared the app with **[Rnote](https://github.com/flxzt/rnote)**, which has similar functionalities to this app, it's clearly showed that it properly uses hardware acceleration, thus usable on my device as shown in the screen recording below:

https://user-images.githubusercontent.com/1403194/168757157-1157e4dc-05b3-4bdb-b7c1-c723805955df.mp4

### Steps to reproduce the bug

1. Open an image.
2. Try to draw.
3. The line won't follow the user input, thus unusable.

## System

- Device (desktop computer/tablet/phone/...): laptop.
- OS: Fedora 36 Workstation 64-bit
- Desktop environment: GNOME
- Package format: Flatpak
- App version: 1.0.1

Reproduce the lag by opening an image and drawing in the Flatpak on Fedora 36 with GNOME, while checking GPU activity with intel_gpu_top. Compare the behavior with Rnote and use the supplied recordings and hardware details to establish whether editing performance improves; done means drawing follows user input smoothly on the reported laptop.

Written by the indexing model from the issue text.