Sparrow Forum

1. 

   finefin
   Member

   hi there! first, let me thank you for this great framework.
   It seems to be exactly what I need now

   I worked through that balloon action game tutorial. everything works fine and fluid. great stuff so far!

   but now I want to animate several objects *without* tweening,
   but in the onEnterFrame method.
   What would be the best approach to have, let's say, 10 balls moving&bouncing around?

   moveX = 1;
   moveY = -1;
   ball.x += moveX;
   ball.y += moveY;

   Do I need to create a Ball-class which contains the onEnterFrame method?
   Could anyone show me an exapmle?
   Or is there another/better way to do this?

   any suggestions would be appreciated

   Posted 1 year ago #
2. 

   finefin
   Member

   okay. I found this thread http://forum.sparrow-framework.org/topic/onenterframe-physics-tweens-blurry-images where my question is anwered (kind of).

   and I took a deeper look into the demo app.
   In the benchmark section the rotation of the sprites inside the onClipEvent method i found this:

   for (SPDisplayObject *child in mContainer)
   child.rotation += 0.05f;

   well, this is very helpful to understand how it works.
   but what should I do to move these childs individually?
   I want every child to have an individual speed
   and bounce off "walls" (screen boundaries).
   can I do something like:

   ball.x += ball.moveX;
   if (ball.x >= 320)
   ball.moveX *= -1;

   ???

   Posted 1 year ago #
3. 

   freerunnering
   Moderator

   If your looking for physics then it might be an idea to look into adding box2d to the project rather then your own physics?

   Posted 1 year ago #
4. 

   finefin
   Member

   hi, thanks for the reply.
   but no. I don't need a physics engine (yet).
   First, i just want to display several sprites moving *individually*.

   As the documentation says: "you can move your enemies, let snowflakes fall down just a little further, etc." - that is nearly what I want to achieve.

   I want every single ball/enemy/snowflake to have it's own enterFrame method, with it's own variables and behaviour.

   EDIT: uh... I'm beginning to think that I am really dumb and asking for something I did a hundred times before...

   Posted 1 year ago #
5. 

   baike
   Moderator

   You can make a Ball class and give it an onEnterFrame method that listens for the corresponding event, but that does introduce a lot of function call overhead that may not be necessary. Instead, you can make a BallController class that contains an array of Balls and just register a single onEnterFrame listener which processes all the Balls. So you'd just do like in your example:
   

   // In BallController class
   - (void)onEnterFrame:(SPEvent *)event {
   	for (Ball *ball in BallCollection) {
   		ball.x += [ball moveX];
   		ball.y += [ball moveY];
   		ball.rotation += [ball spin];
   	}
   }

   Then just move the ball movement logic into the Ball class. So when you call moveY, if the ball is below a certain point (ie the ground), then the Ball class would reverse its velocity and moveY would return a negative number until gravity took over again etc. Each Ball would respond to its move calls based on its current situation.

   Posted 1 year ago #
6. 

   finefin
   Member

   thank you. I'm getting closer to figure that out.
   but still have problems with the "display tree architecture", i guess...

   this is what I did so far:

   I created a BallController and a Ball class.
   In the Game.h the controller is initialized like this:

   -- Game.h:
   #import <Foundation/Foundation.h>
   #import "Sparrow.h"
   @class Ball, BallController;
   @interface Game : SPStage {
   BallController *bController;
   SPSprite *playFieldSprite;
   SPSprite *bContainer;
   }
   @property (nonatomic, retain) BallController *bController;

   -- Game.m:
   // inside the initWithWidth method
   bController = [[BallController alloc] initInSprite:bContainer numberOfBalls:10];

   -- BallController.m:
   -(id) initInSprite:(SPSprite*)theContainer numberOfBalls:(NSInteger)numBall{
   int xPos = 10;
   int yPos = 10;
   int i;
   ballCollection = [NSMutableArray array];
   [ballCollection retain];
   for (i=0; i<numBall;i++){
   NSLog(@"new ball!");
   xPos += 10; // move the new ball a bit...
   yPos += 10;
   Ball *newBall = [[Ball alloc]xPosition:xPos yPosition:yPos inSprite:theContainer];
   [ballCollection addObject: newBall];
   }
   return self;
   }

   -- Ball.m:
   - (Ball *)xPosition:(NSInteger)xPos yPosition:(NSInteger)yPos inSprite:(SPSprite *)container{
   SPImage *image = [SPImage imageWithTexture:[SPTexture textureWithContentsOfFile:@"ball.png"]];
   image.x = xPos;
   image.y = yPos;
   [container addChild:image];
   moveX = 1;
   moveY = 1;
   return self;
   }

   The 10 balls appear on the screen, but I can't access them via onEnterFrame:
   when I try to run the onEnterFrame eventListener
   in the BallController.m or the Ball.m, its not firing at all.
   I only can get it working in the main SPStage class.

   And when I try what you suggested ( ball.x += [ball moveX]; etc.)
   the debugger shows the error "invalid operands to binary + (have 'float' and 'id')"

   oh my... I really wish that someone writes a tutorial on this topic...
   however, any help is welcome

   Posted 1 year ago #
7. 

   Daniel
   Primary Feather

   Hi!

   One thing you have to take care of is that the enter frame event listener will only fire if the object that you add it to must be part of the display list (-> it must be a child, grandchild, etc. of the stage).

   So, if you add the listener like this:

   [someObject addEventListener:@selector(onEnterFrame:) atObject:self
     forType:SP_EVENT_TYPE_ENTER_FRAME];

   then 'someObject' must be a part of the stage.

   Concerning the movement: I think you are expecting this to be more complicated than it is Every display object has x, y, scaleX, scaleY, etc. properties, that define its position on the stage. When you run a code like this:

   object.x += 1;

   then the object will be one pixel further to the right. Thus, if you call this code once per frame, it will move one pixel to the right in every frame. The same can be done with all properties.

   And an enter frame event listener is just a function that is called once per frame. So it's perfect for adding such stuff there.

   I guess in the code from baike ([ball moveX]), 'moveX' is supposed to be a property that returns the number of pixels that the object should be moved per frame, in other words: the x velocity. You have to create that method yourself, if you want to do it that way.

   I hope that helps!

   Posted 1 year ago #
8. 

   finefin
   Member

   okay. thanks for the reply.
   I managed to create some balls on a stage and they are moving around.
   But to me it doesn't seem right. I mean. it does work, but I have the feeling it's a dirty hack and there will be problems when I try to make a game out of it...

   please, could somebody look over it?
   http://dl.dropbox.com/u/4175049/_GotBalls.zip

   btw. I would have the time to write a tutorial about it.
   But first I have to understand it myself

   thanks

   Posted 1 year ago #

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