DXF writer needs methods to write colors

[mme1950]

IDxfStreamWriter has no dedicated methods to write CM and EN colors. The interface should be extended and the implementation should be added.

[DomCR]

I've been looking at this particular issue and it seems that DXF does not support true colors when these are saved by a different code than 420 like, DimensionStyle.DimensionLineColor which is saved with code 176.

To do this test I've saved the file in color_samples as a DXF and manually checked the values stored:

As the image shows the true color has been stored as the closest index color instead of the true color value.

[mme1950]

In the DimensionStyle Object colors are documented with type BS. So this cannot be a true color. An alternative group code for a true color value such as 420 is not specified. But the group-code pair 62/420 seems to be typical for an EN color, dosn't it?

Colors in MultiLeader and MultiLeaderStyle are BLs, thus can store true colors. see Example in #323.

But we have this 0xC000000 value that does not fit into the scheme.

[mme1950]

Hi @DomCR ,

please look at this DXF fragment. The colors BS 176 and BS 177 from DimensionStyle are overridden by extended data in the Dimension object (Acad_TC, DSTYLE_TC).

So obviously DimensionStyle does not support true colors, but Dimension does via extended data. The data structures seem to be the same in DWG.

  0
DIMENSION
  5
2BC
330
1F
100
AcDbEntity
  8
0
100
AcDbDimension
280
     0
  2
*D1
 10
145.8763549700604
 20
162.4105217066659
 30
0.0
 11
109.3947382726832
 21
132.3438146722331
 31
0.0
 70
    33
 71
     5
 42
94.45399835668737
 73
     0
 74
     0
 75
     0
  3
ISO-25
100
AcDbAlignedDimension
 13
86.53582406359419
 23
87.18638064426068
 33
0.0
 14
156.6480200168462
 24
150.4780687571392
 34
0.0
1001
ACAD
1000
DSTYLE
1002
{
1070
   177
1070
   215
1070
   176
1070
    82
1002
}
1001
Acad_TC
1000
DSTYLE_TC
1002
{
1070
   177
1004
1800000002000000985CA3C2000000000000000000000000
1070
   176
1004
18000000020000001FE028C2000000000000000000000000
1002
}
  0

[DomCR]

You are right, I need to take an extensive look on how can we link all this data to the data that is stored in the CadDocument.

[mme1950]

I think, in DXF we have these cases (hopefully this is all ??):

• EN colors, using different group codes for index colors, true colors, and color names
• CM colors with BS group codes that do not support true colors
• CM colors with BL group codes that support index colors, true colors,
• and the strange 0xC0000000 value

I did not find anything about color names and color books for CM colors in the DXF documentation.

Writing extended data is a different story.