Impress/Performance

pngperf cws

Started by hdu few months ago. It improves loading speed of png images and adds possibility to load preview sized png and jpeg images.

Previews

png images can be saved in interlaced mode. It has 2D interlacing, working on cells of 8x8 pixels. Thus it is possible to load slightly lower quality preview image upto 64 times faster. Without it you can for example end with loading few megabytes image - only to compute a small preview containing 64x64 pixels. (see http://www.libpng.org/pub/png/pngintro.html for interlaced example)

jpeg image format contains data stored hierarchicaly and thus can even provide high quality preview images. pngperf cws adds necessary API for doing it.

API

So far there is API for previews, but OOo doesn't use it yet.

There exist slidesorter-demo-* patches in ooo-build http://cvs.gnome.org/viewcvs/ooo-build/patches/src680/ to use pngperf API, but they have still some problems (such as impress sometimes showing preview quality images in slideshow presentation). There is problem with using that API, as Sun needs to keep API/ABI compatability, and thus it is now only possible to set parameters to png/jpeg loaders by static functions.

Things TODO:

• use/fix API usage so that preview size images are used when possible
• save png images in interlace mode to the documents