guideinput.html

VC5.6.7的一个扩展库。跟DirectX的功能差不多。

    break;</PRE
></DIV
><P
>Ideally the code here should use <TT
CLASS="STRUCTFIELD"
><I
>event.jaxis.value</I
></TT
> to scale something. For example lets assume you are using the joystick to control the movement of a spaceship. If the user is using an analog joystick and they push the stick a little bit they expect to move less than if they pushed it a lot. Designing your code for this situation is preferred because it makes the experience for users of analog controls better and remains the same for users of digital controls.</P
><P
>If your joystick has any additional axis then they may be used for other sticks or throttle controls and those axis return values too just with different <TT
CLASS="STRUCTFIELD"
><I
>event.jaxis.axis</I
></TT
> values.</P
><P
>Button handling is simple compared to the axis checking.</P
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN203"
></A
><P
><B
>Example 3-6. Joystick Button Events</B
></P
><PRE
CLASS="PROGRAMLISTING"
>    case SDL_JOYBUTTONDOWN:  /* Handle Joystick Button Presses */
    if ( event.jbutton.button == 0 ) 
    {
        /* code goes here */
    }
    break;</PRE
></DIV
><P
>Button checks are simpler than axis checks because a button can only be pressed or not pressed.  The <TT
CLASS="LITERAL"
>SDL_JOYBUTTONDOWN</TT
> event is triggered when a button is pressed and the <TT
CLASS="LITERAL"
>SDL_JOYBUTTONUP</TT
> event is fired when a button is released. We do have to know what button was pressed though, that is done by reading the <TT
CLASS="STRUCTFIELD"
><I
>event.jbutton.button</I
></TT
> field.</P
><P
>Lastly when we are through using our joysticks we should close them with a call to <A
HREF="sdljoystickclose.html"
><TT
CLASS="FUNCTION"
>SDL_JoystickClose</TT
></A
>. To close our opened joystick 0 we would do this at the end of our program:
<PRE
CLASS="PROGRAMLISTING"
>    SDL_JoystickClose(joystick);</PRE
></P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="AEN214"
></A
>Advanced Joystick Functions</H2
><P
>That takes care of the controls that you can count on being on every joystick under the sun, but there are a few extra things that SDL can support.  Joyballs are next on our list, they are alot like axis with a few minor differences.  Joyballs store relative changes unlike the the absolute postion stored in a axis event. Also one trackball event contains both the change in x and they change in y.  Our case for it is as follows:</P
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN217"
></A
><P
><B
>Example 3-7. Joystick Ball Events</B
></P
><PRE
CLASS="PROGRAMLISTING"
>    case SDL_JOYBALLMOTION:  /* Handle Joyball Motion */
    if( event.jball.ball == 0 )
    {
      /* ball handling */
    }
    break;</PRE
></DIV
><P
>The above checks the first joyball on the joystick. The change in position will be stored in <TT
CLASS="STRUCTFIELD"
><I
>event.jball.xrel</I
></TT
> and <TT
CLASS="STRUCTFIELD"
><I
>event.jball.yrel</I
></TT
>.</P
><P
>Finally we have the hat event. Hats report only the direction they are pushed in. We check hat's position with the bitmasks:

<P
></P
><TABLE
BORDER="0"
><TBODY
><TR
><TD
><TT
CLASS="LITERAL"
>SDL_HAT_CENTERED</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>SDL_HAT_UP</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>SDL_HAT_RIGHT</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>SDL_HAT_DOWN</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>SDL_HAT_LEFT</TT
></TD
></TR
></TBODY
></TABLE
><P
></P
>

Also there are some predefined combinations of the above:
<P
></P
><TABLE
BORDER="0"
><TBODY
><TR
><TD
><TT
CLASS="LITERAL"
>SDL_HAT_RIGHTUP</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>SDL_HAT_RIGHTDOWN</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>SDL_HAT_LEFTUP</TT
></TD
></TR
><TR
><TD
><TT
CLASS="LITERAL"
>SDL_HAT_LEFTDOWN</TT
></TD
></TR
></TBODY
></TABLE
><P
></P
>

Our case for the hat may resemble the following:</P
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN244"
></A
><P
><B
>Example 3-8. Joystick Hat Events</B
></P
><PRE
CLASS="PROGRAMLISTING"
>    case SDL_JOYHATMOTION:  /* Handle Hat Motion */
    if ( event.jhat.value &#38; SDL_HAT_UP )
    {
        /* Do up stuff here */
    }

    if ( event.jhat.value &#38; SDL_HAT_LEFT )
    {
        /* Do left stuff here */
    }

    if ( event.jhat.value &#38; SDL_HAT_RIGHTDOWN )
    {
        /* Do right and down together stuff here */
    }
    break;</PRE
></DIV
><P
>In addition to the queries for number of joysticks on the system and their names there are additional functions to query the capabilities of attached joysticks:
<P
></P
><TABLE
BORDER="0"
><TBODY
><TR
><TD
><A
HREF="sdljoysticknumaxes.html"
><TT
CLASS="FUNCTION"
>SDL_JoystickNumAxes</TT
></A
></TD
><TD
>Returns the number of joysitck axes</TD
></TR
><TR
><TD
><A
HREF="sdljoysticknumbuttons.html"
><TT
CLASS="FUNCTION"
>SDL_JoystickNumButtons</TT
></A
></TD
><TD
>Returns the number of joysitck buttons</TD
></TR
><TR
><TD
><A
HREF="sdljoysticknumballs.html"
><TT
CLASS="FUNCTION"
>SDL_JoystickNumBalls</TT
></A
></TD
><TD
>Returns the number of joysitck balls</TD
></TR
><TR
><TD
><A
HREF="sdljoysticknumhats.html"
><TT
CLASS="FUNCTION"
>SDL_JoystickNumHats</TT
></A
></TD
><TD
>Returns the number of joysitck hats</TD
></TR
></TBODY
></TABLE
><P
></P
>

To use these functions we just have to pass in the joystick structure we got when we opened the joystick. For Example:</P
><DIV
CLASS="EXAMPLE"
><A
NAME="AEN265"
></A
><P
><B
>Example 3-9. Querying Joystick Characteristics</B
></P
><PRE
CLASS="PROGRAMLISTING"
>    int number_of_buttons;
    SDL_Joystick *joystick;

    joystick = SDL_JoystickOpen(0);
    number_of_buttons = SDL_JoystickNumButtons(joystick);</PRE
></DIV
><P
>This block of code would get the number of buttons on the first joystick in the system.	</P
></DIV
></DIV
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="guidevideoopengl.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="guideinputkeyboard.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Using OpenGL With SDL</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="guide.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Handling the Keyboard</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>