Function PlayerTextDrawFont change the font of a player-textdraw.
Function PlayerTextDrawFont was added in 0.3e and will not work in earlier versions!

(playerid, PlayerText:text, font)
int playerid The ID of the player whose player-textdraw to change the font of.
int text The ID of the player-textdraw to change the font of.
int font There are four font styles as shown below. A font value greater than 3 does not display, and anything greater than 16 crashes the client.

Available Styles:
Available Fonts:

Return Values:
This function does not return any specific values.

new PlayerText:welcomeText[MAX_PLAYERS];
public OnPlayerConnect(playerid)
    // First, create the textdraw
    welcomeText[playerid] = CreatePlayerTextDraw(playerid, 240.0, 580.0, "Welcome to my SA-MP server");
    // Set the font of player-textdraw 'welcomeText' to 2.
    PlayerTextDrawFont(playerid, welcomeText[playerid], 2);

Related Functions
The following functions may be useful, as they are related to this function in one way or another.