[Gambas-user] more trigonometry fun (not)

[Kevin Fishburne]

On 05/24/2011 12:16 AM, Bruce Bruen wrote:
> On 24/05/11 13:14, Kevin Fishburne wrote:
>> I was already helped graciously in figuring out how to translate a point
>> in a plane along its local axes at a given orientation, but now need a
>> bit of the inverse of the equation.
>>
>> I need to know the (x, y) offset of a point at a given orientation and
>> velocity. For example if a point is moving at an angle of 45 degrees (or
>> radians, take your pick), what would its x and y coordinate be
>> increased/decreased by? The variables I can think of would be:
>>
>> x1 (point's current x coordinate)
>> y1 (point's current y coordinate)
>> a (point's angle/orientation in degrees/radians)
>> v (point's velocity)
>> x2 (x coordinate offset of point's new position)
>> y2 (y coordinate offset of point's new position)
>>
>> The calculation would take x1, y1 a and v as inputs and produce x2 and
>> y2 as offsets (x1 + x2, y1 + y2 = point's new position).
>>
>> There really should be a list of basic things like this for graphics
>> programmers. I've searched for years and found practically nothing.
>> Weird, considering this has probably been done thousands of times since
>> the days of DOS. :/
>>
>> In case anyone's wondering why I need this, the equation will allow
>> particles and projectiles to follow logical paths. Currently they're
>> bound to local coordinates and ignore player orientation. Digging,
>> shooting arrows, throwing objects, etc. can't work without it.
>>
>>
> 1) Need to include i being the time increment in the same units as velocity
> 2) Basic physics says point will move d units in i time increments according
> to distance=velocity * time . So point will have a deltaXY of v*i.
> Basic trig converts this to deltaX and deltaY using the old "Sign On
> Here 'Coz Alf Has Tan OverAlls"
> deltaX = deltaXY * sin(a)
> deltaY=deltaXY *cos(a)
>
> Bobs, yer uncle, return deltaX and deltaY!

Very true. I didn't want to include time because I didn't want to 
complicate the issue. Time is basically whatever number I multiply the 
velocity by in the mystical and unknown equation. In my case time is a 
single rendering frame, so it's not currently tied to any real sense of 
the word "time".

While I appreciate the hint, what's the equation for DeltaX/Y using 
Sin/Cos/Tan if that is what's being used? I think you may be a bit more 
under the weather than I. :) And it's not even Friday... Fortunately 
when I cross the threshold I stop programming and write music for the 
game. A much more forgiving medium for sure.

-- 
Kevin Fishburne
Eight Virtues
www: http://sales.eightvirtues.com
e-mail: sales at ...1887...
phone: (770) 853-6271