[gameprogrammer] Re: RES: RES: Re: RES: Re: DirectX Line and Triangle
- From: "Alan Wolfe" <alan.wolfe@xxxxxxxxx>
- To: gameprogrammer@xxxxxxxxxxxxx
- Date: Tue, 15 Jul 2008 10:10:21 -0700
Well in your case i think going w/ a pyramid might be easier because if you
use a flat triangle you might want to make it billboarded (or partially
billboarded) where it is always perpendicular to how the person is looking
at it which involves a lot more math!
Since you are in 3d and not 2d what you might have better luck with is
making a pyramid "model" that has a center of 0,0 and is pointing to the
right (like you would see on a regular horizontal line).
Then what you do is when you want to render one of these pyramids on a line,
you calculate how much you should rotate the pyramid on the Y and Z axis to
point along the line (by finding the angles of the line), then render the
pyramid rotated that amount at the midpoint of the line.
you could store this pyramid in a vertex buffer if you wanted to and it
should render really quickly.
You could also make these pyramids rotate on the X axis over time so that
they were slowly spinning when the player was looking at them which might be
a cool effect for your purposes (:
to calculate how much to rotate the pyramid you are going to have to use
something like arc tangent (make sure and use atan2 instead of atan, check
the docs on those to find out why).
On 7/14/08, Edilson Vasconcelos de Melo Junior <dirso@xxxxxxxxxxxxxxxxxx>
wrote:
>
> BTW: The flat triangle was just an idea. It could be a cone or a pyramid
> or anything else that could indicate the driving way. Anything easy and of
> course that DirectX could draw 5,000 on screen without drastically reducing
> de frame rate.
>
>
>
> Thanks,
>
> Dirso
>
>
>
> *De:* gameprogrammer-bounce@xxxxxxxxxxxxx [mailto:
> gameprogrammer-bounce@xxxxxxxxxxxxx] *Em nome de *Edilson Vasconcelos de
> Melo Junior
> *Enviada em:* segunda-feira, 14 de julho de 2008 20:41
> *Para:* gameprogrammer@xxxxxxxxxxxxx
> *Assunto:* [gameprogrammer] RES: Re: RES: Re: DirectX Line and Triangle
>
>
>
> The triangle is really a flat triangle, it's just something to indicate a
> path. And the line segments do have x,y and z values. I work on this project
> like google earth 3d client and my task is to draw lines representing
> streets and make triangles over them pointing the allowed driving way.
>
>
>
> Thanks,
>
> Dirso
>
>
>
> *De:* gameprogrammer-bounce@xxxxxxxxxxxxx [mailto:
> gameprogrammer-bounce@xxxxxxxxxxxxx] *Em nome de *Alan Wolfe
> *Enviada em:* segunda-feira, 14 de julho de 2008 19:22
> *Para:* gameprogrammer@xxxxxxxxxxxxx
> *Assunto:* [gameprogrammer] Re: RES: Re: DirectX Line and Triangle
>
>
>
> the triangle you want to put on the lines, do you want it to be 3
> dimensional (ie a pyramid, not a triangle?) or do you want it to just really
> be a triangle.
>
>
>
> also, when you say you are in 3d do you mean that your line segments all
> have different X,Y and Z values? or are they all on the same Z value?
>
>
>
> On 7/14/08, *Edilson Vasconcelos de Melo Junior* <dirso@xxxxxxxxxxxxxxxxxx>
> wrote:
>
> Hi,
>
>
>
> I'm in 3d… can you help me a little more?
>
>
>
> Thank you very much for your help,
>
> Dirso
>
>
>
> *De:* gameprogrammer-bounce@xxxxxxxxxxxxx [mailto:
> gameprogrammer-bounce@xxxxxxxxxxxxx] *Em nome de *Alan Wolfe
> *Enviada em:* segunda-feira, 14 de julho de 2008 17:38
> *Para:* gameprogrammer@xxxxxxxxxxxxx
> *Assunto:* [gameprogrammer] Re: DirectX Line and Triangle
>
>
>
> Hey Dirso,
>
>
>
> Here's a plan of attack (assuming you are in 2d)
>
>
>
> Calculate the normal of the line segment to get a normalized vector
> perpendicular to the line, this will be useful to figure out the vertices
> for the flat back side of the triangle. Call this NX and NY.
>
>
>
> Calculate the normalized vector of the line, call this LX and LY.
>
>
>
> Find the midpoint of the line call this MX and MY.
>
>
>
> Figure out how wide and how tall you want the triangle to be, call this
> TWidth and THeight.
>
>
>
> If you do the above, here's how to find each of the 3 vertices for the
> triangle for each line:
>
>
>
> Vertex 1:
>
> *start at the midpoint
>
> *subtract LX,LY multiplied by TWidth/2
>
> *add NX,NY * THeight/2
>
>
>
> Vertex 2:
>
> *start at the midpoint
>
> *add LX,LY * TWidth/2
>
>
>
> Vertex 3:
>
> *start at the midpoint
>
> *subtract LX,LY multiplied by TWidth/2
>
> *subtract NX,NY * THeight/2
>
>
>
> That will give you the vertices in a clockwise order, so watch out for back
> face culling if you have clockwise culled (:
>
>
>
>
> On 7/14/08, *Edilson Vasconcelos de Melo Junior* <dirso@xxxxxxxxxxxxxxxxxx>
> wrote:
>
> Hi,
>
>
>
> I have a CustomVertex.PositionColored[] object that represents a line and
> I use the DrawUserPrimitives(PrimitiveType.LineStrip, this.linePoints.Length
> - 1, this.linePoints); to draw it on screen
>
> Now I need to draw a small triangle aligned to each line segment and one of
> each vertex must "pointy" to the finish point of the segment. How can I do
> that?
>
> Something like the attached picture, but not that ugly.
>
>
>
> Thanks,
>
> Dirso.
>
>
>
>
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>
>
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