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  1. Minecraft: Java Edition
  2. MC-89043

Slime blocks moved by pistons often fail to bounce up the player

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    • Icon: Bug Bug
    • Resolution: Fixed
    • 20w07a
    • Minecraft 15w38b, Minecraft 15w39b, Minecraft 15w39c, Minecraft 15w41b, Minecraft 15w42a, Minecraft 15w45a, Minecraft 15w46a, Minecraft 15w47a, Minecraft 15w47b, Minecraft 15w47c, Minecraft 15w49a, Minecraft 15w49b, Minecraft 15w50a, Minecraft 1.9 Pre-Release 2, Minecraft 1.9 Pre-Release 3, Minecraft 1.9 Pre-Release 4, Minecraft 1.9, Minecraft 1.9.1 Pre-Release 1, Minecraft 1.9.1 Pre-Release 2, Minecraft 1.9.1 Pre-Release 3, Minecraft 1.9.1, Minecraft 1.9.2, Minecraft 16w14a, Minecraft 16w15a, Minecraft 16w15b, Minecraft 1.9.3 Pre-Release 1, Minecraft 1.9.3 Pre-Release 2, Minecraft 1.9.3 Pre-Release 3, Minecraft 1.9.3, Minecraft 1.9.4, Minecraft 16w20a, Minecraft 16w21a, Minecraft 16w21b, Minecraft 1.10 Pre-Release 1, Minecraft 1.10 Pre-Release 2, Minecraft 1.10, Minecraft 1.10.2, Minecraft 16w43a, Minecraft 16w44a, Minecraft 1.11 Pre-Release 1, Minecraft 1.11, Minecraft 16w50a, Minecraft 1.11.1, Minecraft 1.11.2, Minecraft 17w06a, Minecraft 1.12, Minecraft 1.12.1 Pre-Release 1, Minecraft 1.12.1, Minecraft 1.12.2 Pre-Release 1, Minecraft 1.12.2 Pre-Release 2, Minecraft 1.12.2, Minecraft 17w43a, Minecraft 17w43b, Minecraft 17w45a, Minecraft 17w45b, Minecraft 18w20b, Minecraft 1.13-pre1, Minecraft 1.13-pre2, Minecraft 1.13-pre3, Minecraft 1.13-pre4, Minecraft 1.13-pre6, Minecraft 1.13-pre7, Minecraft 1.13-pre8, Minecraft 1.13, Minecraft 1.13.1, Minecraft 1.13.2, Minecraft 18w48a, Minecraft 18w48b, Minecraft 18w49a, Minecraft 18w50a, Minecraft 19w02a, Minecraft 19w03c, Minecraft 19w04a, Minecraft 19w04b, Minecraft 19w05a, Minecraft 19w06a, Minecraft 19w07a, Minecraft 19w08b, Minecraft 1.14 Pre-Release 2, Minecraft 1.14 Pre-Release 3, Minecraft 1.14, Minecraft 1.14.2 Pre-Release 2, 1.14.4, 19w37a, 1.15 Pre-release 1, 1.15 Pre-Release 2, 1.15 Pre-release 3, 1.15 Pre-release 4, 1.15 Pre-release 5, 1.15 Pre-release 6, 1.15 Pre-release 7, 1.15, 1.15.1, 1.15.1 Pre-release 1, 1.15.2 Pre-Release 1, 1.15.2 Pre-release 2, 1.15.2, 20w06a
    • Confirmed
    • Player, Redstone
    • Normal

      The bug

      When a piston moves a slime block players are not always launched.

      How to reproduce

      1. Place a upwards facing sticky piston
      2. Place a slime block on top
      3. Place a redstone block on the side of the slime block
      4. Update the piston
      5. Jump on the slime block (which now moves up and down)
        → You will see that you just rarely get bounced up. For entities other than the player it works fine.

      Example

      This video shows it: https://www.youtube.com/watch?v=qgFt5L5f9jY

      Additional information

      It works fine for other entities, so it probably has to do with the client/server communication or similar.

      Potential Fix

      I noticed there is a flag called "velocityChanged" in MCP for entities. It is for example used when an entity is hit and needs to get knock back.

      When the flag is set, the EntityTracker will send an extra packet containing the entities velocity.
      Setting this flag when an entity is bounced by a slime block pretty much fixes this issue. (There is still an related one that if you fall on a moving slime block you don't get bounced which might have similar effects.)

      Video with a comparison flag set vs flag not set: https://www.youtube.com/watch?v=VKHBJxtSlc0&t=2m42s

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            Unassigned Unassigned
            panda4994 [Mojang] Panda
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              Created:
              Updated:
              Resolved:
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