PDFs containing pages with high resolution TIFFs render slowly

[zxqx]

Attach (recommended) or Link to PDF file here: TEST.pdf - a contrived document containing pages with high resolution TIFFs (6592x5100)

Configuration:

• Web browser and its version: Chrome 80.0.3987.87
• Operating system and its version: macOS Mojave (10.14.6)
• PDF.js version: v2.3.200 and latest unstable
• Is a browser extension: No

Steps to reproduce the problem:

1. Upload TEST.pdf using the Mozilla PDF.js demo
2. Scroll down to the last page

What is the expected behavior? The last page renders in a reasonable amount of time.

What went wrong? The last page takes ~15-30 seconds to render.

[Snuffleupagus]

Rendering times improved significantly with PR #17946 (almost 50% in my quick tests), which combined with the pre-existing caching of global image-data means that we've done everything that we realistically can to fix this.