onePassRenderingScaleThreshold property
If a page is rendered over the scale threshold, the page is rendered with the threshold scale and actual resolution image is rendered after some delay (progressive rendering).
Basically, if the value is larger, the viewer renders each page in one-pass rendering; it is faster and looks better to the user. However, larger value may consume more memory. So you may want to set the smaller value to reduce memory consumption.
The default is 200 / 72, which implies rendering at 300 dpi. If you want more granular control for each page, use getPageRenderingScale.
Implementation
final double onePassRenderingScaleThreshold;