What you are looking for is not currently [directly] provided in Blocs.
This technique most commonly uses libraries such as “Masonry” or the newer replacement “Isotope” or other similar alternatives.
These offer features such as:
- Lazy Loading
For portfolios and a vast amount of sites where work type and images can range dramatically across categories, it is a very common solution for providing an elegant display of various categories and work types and is found on many modern websites
Myself and others have suggested this style of library to be integrated into Blocs in the past. Given it’s vast popularity and clear feature benefits I think it would be an asset to users. I hope based upon @Norm's answer above that it does not mean it never will be.
Presently you're only options are:
To do editing of the exported HTML / CSS / JS files from Blocs to implement such libraries as needed via a Text/Code Editor. Or you can try to leverage implementing things via the simple HTML Widget Bric + Custom Classes and via the Page Settings for adding code resources. If not, then you would have to implement via a Text/Code Editor post export. If doing it post export however, the only down side of this is it would need to be manually done every time you re-export your Blocs site, back into the associated exported files each time.