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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

what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
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
what is the stm
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
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
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
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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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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