8000 Add multiplicative blending by brisvag · Pull Request #7868 · napari/napari · GitHub
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Add multiplicative blending #7868

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Merged
merged 2 commits into from
May 13, 2025
Merged

Add multiplicative blending #7868

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c19f896
add multiplicative blending
brisvag Apr 29, 2025
7ee369d
Merge branch 'main' into feature/multiplicative-blending
brisvag May 5, 2025
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7 changes: 7 additions & 0 deletions napari/_vispy/utils/gl.py
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Original file line number Diff line number Diff line change
Expand Up @@ -161,4 +161,11 @@ def fix_data_dtype(data: npt.NDArray) -> npt.NDArray:
'blend': True,
'blend_equation': 'min',
},
'multiplicative': {
'depth_test': False,
'cull_face': False,
'blend': True,
'blend_func': ('dst_color', 'zero', 'one', 'one'),
'blend_equation': 'func_add',
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@brisvag can you explain to me how this work? The func_add really threw me. 😂

what are the contents of the blend_func tuple?

Maybe a comment here would be interesting.

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@brisvag brisvag May 12, 2025 •
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It's trippy, yeah. I learned from https://www.khronos.org/opengl/wiki/Blending#Blending_Parameters

Maybe I'll just put a link, cause this requires some background.

The relevant bits are:

Blending equation:

* Orgb = srgb * Srgb + drgb * Drgb
* Oa = sa * Sa + da * Da

(O = origin, D = destination, small is parameter, capitalized is the value itself)

"For example, if the blending you want is a straight multiplication of the source and destination colors, O = S * D, then you should set the GL_FUNC_ADD function. Then set the source parameter for that equation to GL_DST_COLOR, and set the destination parameter to GL_ZERO (we don't want to do addition, so null out the additive term). This will give O = D * S + 0 * D. "

Basically, we're using the destination color as a parameter for the origin color, and ignoring the destination color itself because it's already accounted for.

},
}
2 changes: 2 additions & 0 deletions napari/layers/base/_base_constants.py
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Expand Up @@ -42,6 +42,7 @@ class Blending(StringEnum):
ADDITIVE = auto()
MINIMUM = auto()
OPAQUE = auto()
MULTIPLICATIVE = auto()


BLENDING_TRANSLATIONS = OrderedDict(
Expand All @@ -51,6 +52,7 @@ class Blending(StringEnum):
(Blending.ADDITIVE, trans._('additive')),
(Blending.MINIMUM, trans._('minimum')),
(Blending.OPAQUE, trans._('opaque')),
(Blending.MULTIPLICATIVE, trans._('multiplicative')),
]
)

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