Support for blending mode "source" for making "holes"

[joachimeibl]

Hi,
My problem is this: I want to make "holes" into an imported bitmap image, so that I can see through to what is below that image.
I can't figure a way to achieve this with currently available possibilities.
I would suggest a blending mode "source" on individual objects.
(Comparable to composition-mode "Source" from QPainter: http://doc.qt.nokia.com/4.6/qpainter.html#CompositionMode-enum)

Currently creating an object with an alpha value allows transparency to the object below. But it does not make a hole into that object because the "normal" blending imitates a real transparent object.

The mode "source" on an object would take the complete RGBA from a pixel and apply it only in the same layer. So if that object is on top in that layer, the alpha value would define how that layer is transparent at that position, regardless, what objects are below. This would be like erasing the objects below in that layer.

Best regards, (you're doing a great job!)
Joachim

[ScislaC (scislac)]

Have you tried using a clippath or mask to achieve what you're looking for?

[su_v (suv-lp)]

If the solution is not based on SVG filters -> see
Bug #412928 “Allow clip/mask set inverse”:
<https://bugs.launchpad.net/inkscape/+bug/412928>

'Inverse clip/mask' with currently available tools:
a) as clip path:
draw a rectangle/object covering your image, subtract a second rectangle/object with size/location of the intended 'hole' and use the result as clip-path.
b) as mask:
draw a solid white rectangle/object covering your image, a black rectangle/object with the size/location of the intended 'hole', group the white and black object and use the group to mask your image.

[su_v (suv-lp)]

… and an example using SVG filters (feImage and feComposite). Enter the group in the top layer and move the (apparently transparent) star.

Note: Firefox 3.5.9 and Safai 4.0.5 don't display the filter effect (feImage), but Squiggle (Batik 1.7) and Opera 10.53 do.

References:
- Inkscape Filter Effects - Compositing Filter Primitives
  <http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Filters-Compositing.html#Filters-Composite>
- SVG 1.1 Specification - 15.12 Filter primitive 'feComposite'
  <http://www.w3.org/TR/SVG11/filters.html#feComposite>
- Example 10-7. Use of feComposite in and out (uses the in and out operators to do "cut-outs.")
  <http://commons.oreilly.com/wiki/index.php/SVG_Essentials/Filters#svgess-CHP-10-EX-7>

[joachimeibl (joachim-eibl)]

Thank you very much for the many examples and references. I didn't know about masks in inkscape/svg. This helped me a lot!
Joachim

[Rob Antonishen (rob-antonishen)]

https://bugs.launchpad.net/inkscape/+bug/587579/+attachment/1410738/+files/cut-filter-3.svg

No longer seems to work in the current development builds? Has fecomposite been broken?