test/Documentation/Skill/skill-learn-flow.md

Skill Learn Flow (C++)

1. CDlgSkillSubListItem::OnCommand_Upgrade

   • Triggered when the player clicks the learn/upgrade button on a skill.
   • Performs status checks (dead, trading, etc.), evaluates CheckLearnCondition, and shows the Game_LearnSkill confirmation dialog.
   • If the NPC greeting has not been received yet, calls CECHostSkillModel::SendHelloToSkillLearnNPC().

2. CECHostSkillModel

   • Maintains m_skillLearnNPCNID, the NPC ID that currently offers skill learning.
   • ProcessServiceList() scans cmd_scene_service_npc_list from the server, keeps the valid NPC, and resets m_bReceivedNPCGreeting when a new NPC is selected.
   • SendHelloToSkillLearnNPC() issues c2s_CmdNPCSevHello(m_skillLearnNPCNID) to start the NPC service handshake.
   • OnNpcGreeting() is invoked when NPC_GREETING (cmd 70) arrives; it marks the greeting as received so future learns skip re-hello.

3. CDlgSkillAction::TryOpenDialog

   • Called when the skill dialog is being opened (skill vs action mode).
   • If the host isn’t currently “talking with the NPC,” it forces the dialog to open, sends SendHelloToSkillLearnNPC(), and clears the “received greeting” flag so the next dialog confirms again.

4. Game UI dialog

   • Player confirms the Game_LearnSkill message box (EC_GameUIMan::OnMessageBoxClose).
   • If IDOK and CheckSkillLearnCondition still returns zero, it sends c2s_CmdNPCSevLearnSkill(skillID).
   • The dialog name "Game_LearnSkill" ensures the server hasn’t rejected the skill because it missed the handshake.

5. Server round-trip

   • SEVNPC_HELLO establishes the NPC service context.
   • Server replies with NPC_GREETING, parsed by GameSession and forwarded to CECHostSkillModel::OnNpcGreeting.
   • Only after the greeting can SEVNPC_SERVE with GP_NPCSEV_LEARN be trusted; else, the server often drops it without a LEARN_SKILL response.

Use this sequence when troubleshooting missing LEARN_SKILL responses: show/confirm dialog → send SEVNPC_HELLO → wait for NPC_GREETING → send GP_NPCSEV_LEARN.