Client Architecture

The client (client/) is the presentation layer of OpenWarcraft3. It owns the SDL2 window, the OpenGL context, the input system, and the connection to the server. It never runs game logic — all simulation takes place on the server.

Startup

The client is initialised by CL_Init in cl_main.c, which:

1. Opens a connection to the server via NET_OpenLoopback (common/net.c).
2. Registers client-side console commands.
3. Sends a clc_connect message to the server.

The server responds with svc_serverdata (map name, game parameters) followed by a stream of entity baselines and the initial UI layout.

Main Loop

CL_Frame(DWORD msec) is called once per rendered frame by the platform layer (common/main.c). It performs the following steps in order:

void CL_Frame(DWORD msec) {
    cl.time += msec;
    CL_ReadPackets();   // 1. apply incoming server messages
    CL_Input();         // 2. sample keyboard / mouse
    CL_SendCommand();   // 3. forward commands to server
    CL_PrepRefresh();   // 4. build scene for the renderer
    SCR_UpdateScreen(); // 5. draw the frame
}

1. CL_ReadPackets

Drains the loopback receive buffer and dispatches each message by its svc_* opcode:

Opcode	Handler	Effect
svc_serverdata	CL_ParseServerData	Store map path, spawn player camera
svc_spawnbaseline	CL_ParseBaseline	Initialise entity s field from delta
svc_packetentities	CL_ReadPacketEntities	Apply per-frame entity delta
svc_layout	CL_ParseLayout	Store serialised UI blob
svc_disconnect	—	Reset client state

2. CL_Input

CL_Input (in cl_input.c) reads the current SDL2 keyboard and mouse state and fills a usercmd_t struct:

typedef struct {
    DWORD  msec;
    DWORD  buttons;   // bitmask of pressed buttons
    SHORT  forwardmove;
    SHORT  sidemove;
    float  angles[3]; // camera Euler angles
} usercmd_t;

Camera rotation is applied to the stored cl.viewangles every frame. Mouse button events are translated to BUTTON_* bitmask bits. Keyboard events produce CL_KeyEvent calls which feed the console and keyboard bindings.

3. CL_SendCommand

Serialises the current usercmd_t as a clc_move message and writes it to the loopback send buffer for the server to read on its next SV_ReadPackets call.

For higher-level actions (right-click, ability use, unit selection), the input code sends dedicated clc_* messages that the server's command dispatcher (game/g_commands.c) handles.

4. CL_PrepRefresh

Builds the render scene: - Sets the camera view origin and angles from cl.viewangles. - Calls CL_AddEntities which iterates cl.entities and calls V_AddEntity for each visible entity. Entities with the EF_NODRAW flag are skipped. - Client-side temporary effects (client/cl_tent.c) add short-lived visual-only entities such as blood splats and hit sparks.

5. SCR_UpdateScreen

Calls into the renderer library: 1. R_BeginFrame — clear colour/depth, update matrices. 2. R_RenderFrame — draw all entities, terrain, water, particles. 3. R_DrawUI — rasterise the cached UI layout blob. 4. R_EndFrame — SDL2 GL_SwapWindow.

Entity Interpolation

The client keeps two snapshots per entity: prev and current. CL_PrepRefresh blends between them using a fraction derived from cl.time and the server frame interval, producing smooth motion even when the client render rate exceeds the server tick rate.

Console and HUD

cl_console.c maintains an in-game console that can be toggled with the tilde key. cl_scrn.c overlays FPS, ping, and debug counters. Neither system communicates with the server.

Key Files

File	Purpose
client/cl_main.c	CL_Frame, CL_Init, CL_ReadPackets
client/cl_input.c	Input sampling, usercmd_t construction
client/cl_parse.c	Server message handlers
client/cl_view.c	Camera, CL_PrepRefresh, V_AddEntity
client/cl_tent.c	Temporary client-side effects
client/cl_scrn.c	HUD / screen overlay
client/cl_console.c	In-game console
client/keys.c	Key event dispatch and binding table
common/net.c	Loopback transport shared by client and server