7 replies to this topic

[Citizen666]

Hi all.

I'm trying to do something very simple as part of my learning XNA and am making a hash of it as usual.

Any help would be greatly appreciated.

So I've got a player controlled sprite that can move around the screen using the KB. All good.
I've now drawn a second stationary sprite on the right hand side of the screen.

What I'm trying to do is display a text message when the player controlled sprite moves over the stationary sprite.

I'm fine with the actual drawing of the text (I think) I just need to work out how to register that moveable Sprite A has indeed moved over stationary sprite B.

Thanks in advance,

Gigi.

[JTippetts]

After reading your title, I now have that Powerman 5000 song When Worlds Collide in my head.

You need to first check for intersection between the bounding boxes of A and B. Each sprite can be envisioned to be enclosed by a box, that it fits tightly inside. Each time a sprite moves, you can use an algorithm such as the separating axis test to determine if the boxes overlap, and if they do then you can return a true value and in your main loop if this true value is returned you can display the text.

[Citizen666]

yeh, I kind of understand the principle and logic behind the test etc - I just don't know the commands and the correct syntax to use....

Edited by Citizen666, 25 September 2012 - 07:45 AM.

[BCullis]

I just don't know the commands and the correct syntax to use....

I'll try to not read that as "please write my code for me" ;p

There isn't a specific command. You implement the algorithm in c#. The separating axis theorem is pretty heavy for what you're talking about though if you're still in an early learning stage. XNA has built in "Bounding_______" structures, you probably just want to create a BoundingBox for each sprite, and then use the built-in BoundingBox.Intersects() method to check for collision/overlap. This can result in some wierd effects if the sprite has a detailed or convex shape that leaves a lot of space in the BoundingBox, but it's a start, and the size of the box can always be tweaked.

Just remember to update the bounding boxes' locations in addition to the sprites' locations when you do your update logic.

[Haps]

These examples from the education catalog are a good place to start, they should show you what you're looking for:

Rectangle collision

Per-Pixel collision

[Zolomon]

After reading your title, I now have that Powerman 5000 song When Worlds Collide in my head.

Sorry, just have to share that I also got the song in my head immediately after reading the title.

[superman3275]

Well, in SFML you set floatrects (Rectangles that can have coordinates that are floating point values) up around the sprite.
Something along the lines of:

sf::floatrect floatrect1;
sf::floatrect floatrect2;
//
// SET FLOATRECTS COORDS TO SPRITES
//
if (floatrect1.Intersects(floatrect2))
{
	  //COLLISION
}

if there isn't an intersect function for bounding boxes, write your own using the coordinates of the floatrects.
(I didn't write down the specific code because I didn't have time, also you might not know SFML/C++)

Edited by superman3275, 25 September 2012 - 10:07 AM.

[Citizen666]

Thanks for the replies all!!

Will now spend time trying to actually implement.