r11 JUMP documentation

[rurban]

r10 and r11 do have a new EXTRAS entities section, which represent replaced objects, which do not have room in the original ENTITY or BLOCKS section. This is not documented in the ODA specs.

This is represented by the new JUMP entity. Each replaced entity is replaced with a JUMP entity, containing the offset into the other section.
The first JUMP is replaced by the entity at the given offset in the extras sections, and then jumps back to the next entity, also given by the offset in the extras JUMP.

See e.g. r10/entities.dwg
The JUMP [31] replaces the POLYLINE_2D entity which got later closed. An open POLYLINE_2D needs size 8, but closed 9 bytes. Hence they added the new closed replacement to the extras section at offset 0, index [66], and added another JUMP [67] back to the next original entity. Here it jumps back to the VERTEX_2D [32] at offset 0x84f.

type: 18 [RCd]
Add entity JUMP [31] Decode entity JUMP
===========================
Entity number: 31, Type: 18, Addr: 847
flag_r11: 0x0 [RC 0]
size: 8 [RS]
jump_address_raw: 0x80000000 [RLx 0]
jump_entity_section: DWG_EXTRA_SECTION
jump_address: 0x0

type: 20 [RCd]
Add entity VERTEX_2D [32] Decode entity VERTEX_2D
===========================
Entity number: 32, Type: 20, Addr: 84f
flag_r11: 0x0 [RC 0]
size: 24 [RS]
layer: 0 [H(RSd) 8]
opts_r11: 0x0 [RSx 0]
point: (5.500000, 7.500000) [2RD 10]

....

extras entities: (0x10c0-0x10d1 (0), size 17)
==========================================
type: 19 [RCd]
Add entity POLYLINE_2D [66] Decode entity POLYLINE_2D
===========================
Entity number: 66, Type: 19, Addr: 10c0
flag_r11: 0x80 [RC 0]
          HAS_ATTRIBS(0x80) 
size: 9 [RS]
layer: 0 [H(RSd) 8]
opts_r11: 0x1 [RSx 0]
          HAS_FLAG(0x1) 
flag: 0x1 [RC 70]
      CLOSED(0x1) 

type: 18 [RCd]
Add entity JUMP [67] Decode entity JUMP
===========================
Entity number: 67, Type: 18, Addr: 10c9
flag_r11: 0x0 [RC 0]
size: 8 [RS]
jump_address_raw: 0x84f [RLx 0]
jump_entity_section: DWG_ENTITY_SECTION
jump_address: 0x84f
==========================================
extras entities: end