Problems with lighting of extruded custom-shapes

[Regina Henschel]

Hi all,

I want to improve lighting for extruded custom-shapes. I have examined 
how MS Office (MSO) does lighting of those shapes. Now I try to map that 
to the attributes of 3D scene and objects, which are used to render 
extruded custom-shapes. I see some problems and things incompatible with 
our current implementation (including my previous commit). So it would 
be nice to get some comments and suggestions from you.

If the OOXML 'scene3d' and 'sp3d' elements will be imported so, that 
extruded custom-shapes are used, the decisions here will influence that 
implementation too.
Fontwork is affected too, because it is only a special mode of a 
custom-shape.

I know that for most of you working on LibreOffice is connected with 
making money. But maybe you have time to think about the problems anyway?


(A)
MSO attributes 'c3DKeyHarsh' and 'c3DFillHarsh'
API properties 'FirstLineHarsh' and 'SecondLineHarsh'
ODF attributes 'draw:extrusion-first-light-harsh' and 
'draw:extrusion-second-light-harsh':

If a light is not "harsh", then MSO keeps only half the intensity value 
at the light and puts the other half to the ambient light. The light 
keeps to be "specular" in the sense of LO. That does not correspond to 
light attribute 'dr3d:specular' in our 3D engine, which is currently used.

ODF specifies, "The means by which the light is softened is 
implementation-defined." That means, that in addition we need to 
document, how we do it.


(B)
MSO attribute 'c3DShininess'
API property 'Shininess'
ODF attribute 'draw:extrusion-shininess':

This attribute has the same effect in MSO as the property "Specular 
Intensity" in the '3D Effects' dialog. That property is ODF style 
attribute 'dr3d:shininess'. Only the value ranges are different and a 
mapping would be not linear. But this attribute is currently not 
evaluated at all for extruded custom-shapes. Instead a value is build as 
100 - "Specularity". (for "Specularity" see below)


(C)
MSO attribute 'c3DDiffuseAmt'
API property 'Diffusion'
ODF attribute 'draw:extrusion-diffusion':

The attribute works on the luminance of the fill color of the shape in 
MSO. I have not yet tested extrusion color. There exists a style 
attribute dr3d:diffuse-color (not to be confused with the same named 
light attribute) for 3D-objects in ODF. But this ODF attribute is not 
implemented in our 3D engine and the standard does not contain a 
description, how it should work. Values are only preserved from load to 
save by LO.
Default value is 1 in MSO and 0% in ODF.
MSO sets this attribute in addition to the 'fc3DMetallic' flag, if the 
user chooses the surface preset 'Metal', so we need to consider it for 
extruded custom-shapes.


(D)
MSO attribute 'c3DSpecularAmt'
API property 'Specularity'
ODF attribute 'draw:extrusion-specularity':

This attribute is currently mapped to property 'Specular color' in the 
'3d Effects' dialog. That property is ODF style attribute 
'dr3d:specular-color'. ODF has as data type zeroToHundredPercent. MSO 
allows values larger as 1 and evaluates them. If the user sets surface 
preset 'Plastic' in the UI, then MSO sets 80000/65536≈122% for example.


(E)
MSO flag 'fc3DMetallic'
API property 'Metal'
ODF attribute 'draw:extrusion-metal':

The ODF standard specifies,
"•false: the specular color for the shading of an extruded shape is white.
•true: the specular color for the shading of an extruded shape is gray 
(red green and blue values of 200) instead of white and 15% is added to 
the specularity."

But "specular color" is not defined in the standard. It cannot be 
interpreted as "color resulting from draw:extrusion-specularity", 
because then that color would be either white or RGB(200,200,200), and 
it would conflict with interpreting 'specularity' as being 
'draw:extrusion-specularity'.
MSO has default 65536 for attribute 'c3DDiffuseAmt' and reduces it to 
43712 in case of surface "Metal". Interpreting 'c3DDiffuseAmt' as 
"specular color" and 65536 as white and 43712 as gray would not result 
in RGB(200,200,200) but in RGB(170,170,170).



In case you want to test these MSO properties in a current MSO, then use 
a text document and save it to RTF. MSO provides then a UI for extruding 
shapes which uses these attributes known from the binary format, and you 
can edit the resulting RTF-file instead of working in binary format. LO 
cannot import the shapes in the RTF-file directly. Instead let MSO save 
it to doc-Format.

Kind regards,
Regina