LETTERS

GAME OUT OF CONTROL
When running the code from Philip McBride's article "Game Controls for QuickDraw
3D" in Issue 27 of develop, I noticed in MySetCameraData that the call to
Q3Camera_SetPlacement gets fouled up after a while. The fix shown below was needed.
void MyGetCameraData(
    DocumentPtr theDocument,
    TQ3CameraObject theCamera)
{
    TQ3CameraPlacement cameraPlacement;
    ...
    Q3Vector3D_Cross(
        &theDocument->zVector,
        &theDocument->yVector,
        &theDocument->zVector);

    // I added this:
    Q3Vector3D_Normalize(
        &theDocument->xVector,
        &theDocument->xVector);
}

 

-- Flip Phillips

You made the right call. QuickDraw 3D requires all vectors to be of unit length
(normalized). So any changes to  vectors that could make them not normalized should
be followed by a call to normalize  those vectors (using Q3Vector3D_Normalize as
you've done). If QuickDraw 3D didn' t have this requirement, it would have to
normalize vectors itself internally, which would take away from its efficiency.
-- Philip McBride

A SIDE ISSUE
In Steve Falkenburg's article "Planning for Mac OS 8 Compatibility" in develop Issue
26, I read the following:

After some poking around, we figured out that it was assuming that InitWindows called
InitMenus as a side effect. The completely new Mac OS 8 implementations of windows
and menus no longer have this behavior.

However, Inside Macintosh Volume V states, under the heading "InitWindows" on page
208:

Since the menu bar definition procedure ('MBDF') actually performs these
calculations, InitWindows now calls InitMenus directly. InitMenus has been modified
so that it can be called twice  in a program without ill effect.

I advise the Mac OS 8 engineers to read the "You're never too smart to read the manual"
section of the Veteran Neophyte column in the same issue of develop ;-).
-- Reinder Verlinde

Your point is well taken. However, it's  worth mentioning that Inside Macintosh:
Macintosh Toolbox Essentials (the more current documentation) says no such thing,
and in fact says explicitly that InitMenus should always be called after InitWindows.
As always, depending on a side effect, even  a documented one, is dangerous.
-- Dave Johnson

MORE GOOD STUFF

Look on this issue's CD and develop's Web site for Martin Minow's article, "Timing on
the Macintosh," which was recently updated to include a few Java timing techniques.
You'll also find some scripting vocabulary advice from Cal Simone.

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