# Line

Also known as a "linedef." A line segment with two sides and two vertices.

```
struct Line play
{
	readonly Sector  BackSector, FrontSector;
	readonly double  BBox[4];
	readonly vector2 Delta;
	readonly Side    Sidedef[2];
	readonly Vertex  V1, V2;

	readonly uint PortalIndex;
	readonly uint PortalTransferred;

	readonly int Health;
	readonly int HealthGroup;

	double Alpha;
	uint   Flags;
	int    ValidCount;

	uint Activation;
	int  Args[5];
	int  LockNumber;
	int  Special;

	int Index();

	bool Activate(Actor activator, int side, int type);
	bool RemoteActivate(Actor activator, int side, int type, vector3 pos);

	Line GetPortalDestination();
	bool IsLinePortal();
	bool IsVisualPortal();

	clearscope int GetHealth();
	void SetHealth(int newhealth);

	double GetUdmfFloat(name nm);
	int    GetUdmfInt(name nm);
	string GetUdmfString(name nm);
}
```

### `BackSector`, `FrontSector`

The sector of the front and back sides of this line.

### `BBox`

The top, bottom, left and right of the line, respective to array index.

### `Delta`

Equivalent to `V2 - V1`.

### `V1`, `V2`

Returns the start and end points of this line segment, respectively.

### `Sidedef`

The front and back sides of this line, 0 and 1 respectively. The aliases
`Line.Front` and `Line.Back` are provided as well.

### `PortalIndex`

TODO

### `PortalTransferred`

TODO

### `Health`

TODO

### `HealthGroup`

TODO

### `Alpha`

Alpha of the middle texture on both sides.

### `Flags`

Any combination of the following bit flags:

| Name                     | Description                                                                       |
| ----                     | -----------                                                                       |
| `ML_3DMIDTEX_IMPASS`     | Middle texture will collide with projectiles and allow them to pass through.      |
| `ML_3DMIDTEX`            | Middle texture can be collided with and walked on as if it were a thin sector.    |
| `ML_ADDTRANS`            | Middle textures are drawn with additive translucency on both sides.               |
| `ML_BLOCKEVERYTHING`     | Line blocks everything.                                                           |
| `ML_BLOCKHITSCAN`        | Line blocks hit scan attacks.                                                     |
| `ML_BLOCKING`            | Line is solid and blocks everything but projectiles and hit scan attacks.         |
| `ML_BLOCKMONSTERS`       | Line blocks non-flying monsters.                                                  |
| `ML_BLOCKPROJECTILE`     | Line blocks projectiles.                                                          |
| `ML_BLOCKSIGHT`          | Line blocks line of sight.                                                        |
| `ML_BLOCKUSE`            | Line blocks use actions.                                                          |
| `ML_BLOCK_FLOATERS`      | Line blocks flying monsters.                                                      |
| `ML_BLOCK_PLAYERS`       | Line blocks players.                                                              |
| `ML_CHECKSWITCHRANGE`    | Checks the activator's vertical position as well as horizontal before activating. |
| `ML_CLIP_MIDTEX`         | Applies `WALLF_CLIP_MIDTEX` to both sides.                                        |
| `ML_DONTDRAW`            | Never shown on the auto-map.                                                      |
| `ML_DONTPEGBOTTOM`       | Lower texture is unpegged on both sides.                                          |
| `ML_DONTPEGTOP`          | Upper texture is unpegged on both sides.                                          |
| `ML_FIRSTSIDEONLY`       | Special can only be activated from the front side.                                |
| `ML_MAPPED`              | Always shown on the auto-map.                                                     |
| `ML_MONSTERSCANACTIVATE` | Monsters may activate this line.                                                  |
| `ML_RAILING`             | Line is a railing that can be jumped over.                                        |
| `ML_REPEAT_SPECIAL`      | Special may be activated multiple times.                                          |
| `ML_SECRET`              | Line will be shown as one-sided on the auto-map.                                  |
| `ML_SOUNDBLOCK`          | Blocks sound propagation after two lines with this flag.                          |
| `ML_TWOSIDED`            | Line has a back side.                                                             |
| `ML_WRAP_MIDTEX`         | Applies `WALLF_WRAP_MIDTEX` to both sides.                                        |
| `ML_ZONEBOUNDARY`        | Reverb zone boundary.                                                             |

### `ValidCount`

Don't use this.

### `Activation`

TODO

### `Args`

Arguments of the line's special action.

### `LockNumber`

TODO

### `Special`

Number of the special action to be executed when this line is activated.

### `Index`

Returns the index of this line.

### `Activate`

TODO

### `RemoteActivate`

TODO

### `GetPortalDestination`

TODO

### `IsLinePortal`

TODO

### `IsVisualPortal`

TODO

### `GetHealth`

TODO

### `SetHealth`

TODO

### `GetUdmfFloat`, `GetUdmfInt`, `GetUdmfString`

Gets a named UDMF property attached to this linedef.

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