In my current project i try to get close to photorealism (don't want to actually achieve it). The scene contains a pool and i need to draw waves. Just drawing them will not give me good results. I don't want sharp edges. Bluring helps, but it can't work like a smudge brush in programs like GIMP. My aim would be close to this: http://gelbooru.com/index.php?page=post&s=view&id=798856 (Ignore the rest of the image )

Any ideas how to achieve this, without slowing Inkscape so much down that i can't work anymore?

Wow, yes, I was thinking of trying to recreate such an effect a while ago. I decided to go with another project in the end. But at the time, I was thinking of starting with the Voronoi Pattern extension. Then Pattern to Objects actually converts it to many paths....which could then be widened, tweaked and edited individually and/or combined and stroked, perhaps with some other sort of custom pattern or texture....and of course some blur would be needed. I haven't worked with masking much myself, but this might a good project for using a mask or 2. I don't think you will be able to achieve that with a single "layer" of work. I think you will have to overlay at least a couple of blurs and/or masks, etc. And you probably already know this but using regular Layers can help with the slowing.

The "waves" in your example are caustics.
a good, free caustics generator is here http://www.dualheights.se/caustics/
You can layer the result in GIMP to get the example effect.
God bless you always, all ways.

Wow, that's amazing!
Do you know what formats the program uses -- vector or raster? I read most of the info on the website, but didn't see that info. EDIT -- Ok, I see "bitmap" mentioned in development history. Not sure if that means raster or BMP format?

You might be able to get a "good enough" approximation using filters. Try something like this:

1) Create a rectangle with the colour of your water
2) Open the filter editor, click "New" on the left and then check the checkbox while your rectangle is selected to apply the new filter to it
3) In the right, select "Turbulence" and click "Add Effect". Play around with the "Base Frequency" parameter to get the right size for the waves. Don't worry about the colour
4) Select the "Composite" effect, then click "Add Effect"
5) The bottom triangle in the composite effect should be attached to the Turbulence effect above it. Drag the top triangle to the "Source graphic" bar at the right.
6) Set the "Operator" parameter to "In"

That should give you a reasonable starting point. I suggest duplicating the rectangle and rotating the dupe to give you crossing lines of waves a bit more like the image you linked to. From there you can play with clipping and skewing to get the perspective you want.

brynn wrote:Wow, that's amazing!
Do you know what formats the program uses -- vector or raster? I read most of the info on the website, but didn't see that info. EDIT -- Ok, I see "bitmap" mentioned in development history. Not sure if that means raster or BMP format?

Uses native format for saving animations and BMP for still images. BMP is a raster format.

Vector format tells computer how to draw the image, like line from point to point and how to fill in closed areas.
Raster format tells computer the color of each pixel, though compressed raster format may say pixels from A to B are (color).
Raster "originally referred to the raster scan of cathode ray tube (CRT) video monitors, which paint the image line by line".
I know, you already knew all that. Old teaching habits are hard to break.

Have used this caustics generator myself and it works well. Output bmp can be easily converted with Irfanview.
God bless you always, all ways.