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The description in the documentation doesn't make a lot of sense to me. I believe it is safe to say, however, that in this XNA program, the viewport is synonymous with the gamewindow. However, that is not always the case. A game window can contain more than one viewport. See How To: Use Viewports for Split Screen Gaming for an example.

Compute the position of the UFO relative to the game window

The code in Listing 4 computes a position vector which, when applied during the drawing of the UFO, will cause the UFO to occupy a position approximatelylike that shown in Figure 4 .

Listing 4 . Compute the position of the UFO relative to the game window.

ufoPosition.X = viewport.Width / 2; ufoPosition.Y = viewport.Height - 70;

I say approximately because one additional adjustment to the position of the UFO will be made later using the origin parameter of the SpriteBatch.Draw method. If that adjustment were not made, the upper left corner of the rectangle that contains the UFO would beplaced at the position computed in Listing 4 . The origin property will be used to center the UFO on the position that is computed in Listing 4 .

Compute the base scale factor for the background image

Listing 5 computes a scale factor which, when applied to the background image during the drawing process, will cause the 640x480 background image to just fitthe game window. Recall that the size of the game window was set in the constructor of Listing 2 taking the aspect ratio of the background image into account.

Listing 5 . Compute the base scale factor for the background image.

backgroundBaseScale = (float)(450.0 / 640.0); }//end LoadContent

Not the only scale factor

The scale factor computed in Listing 5 will be applied to the background image when the program first starts running. However, during most of the runningof the program, a different scale factor will be applied to the background image and the scale factor computed in Listing 5 will be only one component of that overall scale factor.

An optical illusion

The application of a scale factor to the background image that changes with time is what causes the planet to grow in size giving the illusion that the UFOis approaching the surface of the planet.

Listing 5 signals the end of the LoadContent method.

The overridden Update method

The overridden Update method begins in Listing 6 .

Listing 6 . Beginning of the overridden Update method.

protected override void Update(GameTime gameTime) { //Compute the elapsed time since the last update.// Draw new data only if this time exceeds the // desired frame interval given by msPerFramemsElapsed += gameTime.ElapsedGameTime.Milliseconds; if(msElapsed>msPerFrame) { //Reset the elapsed time and draw the frame with// new data. msElapsed = 0;

Controlling the animation speed

The code in Listing 6 is not new to this module. I explained code like this in an earlier module.

Briefly, the Update method is called sixty times per second by default (I didn't change the default). That is too fast to produce ananimation that looks the way I wanted it to look.

Questions & Answers

how can chip be made from sand
Eke Reply
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Almas
are nano particles real
Missy Reply
yeah
Joseph
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
Lale Reply
no can't
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William
currently
William
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Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
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There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
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Bhagvanji
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Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
has a lot of application modern world
Kamaluddeen
yes
narayan
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ya I also want to know the raman spectra
Bhagvanji
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Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
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Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
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Santosh
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Rafiq
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Mahi
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Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
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analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
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Source:  OpenStax, Xna game studio. OpenStax CNX. Feb 28, 2014 Download for free at https://legacy.cnx.org/content/col11634/1.6
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