Cocos2D: Gap in scrolling background

Question

I´ve seen tons of people having this problem but I can´t seem to find a solution for my case. Like the title explains I have a scrolling background, using two sprites containing the same image. I´ve set the height to 321 (321x480) believing that would fix the problem, boy, it did not.

Well, this is my setup in the init:

 background = [CCSprite spriteWithFile:@"level1BG.png"];
        background.position = ccp(background.contentSize.width/2, background.contentSize.height/2);
        [self addChild:background];

        background2 = [CCSprite spriteWithFile:@"level1BG.png"];
        background2.position = ccp(background2.contentSize.width/2, -background2.contentSize.height/2);
        [self addChild:background2];

Nothing fancy here, just an setup.

And this is my schedule scroll(with has a ccTime parameter of course): Oh, the background scrolls upwards, increasing the y-value.

-(void)scroll:(ccTime)dt{
    background.position = ccp(background.position.x, background.position.y + GAME_SPEED*dt);
    background2.position = ccp(background2.position.x, background2.position.y + GAME_SPEED*dt);

    if(background.position.y >= background.contentSize.width){
        background.position = ccp(background.position.x, -background.contentSize.height/2 + 1);
    }else if(background2.position.y >= background2.contentSize.width){
        background2.position = ccp(background2.position.x, -background2.contentSize.height/2 + 1);

    }
}

GAME_SPEED is defined to 50.0. I´ve added the "+ 1" believing THAT would fix the problem, wrong again though!

So, to the question, does anyone know a way to remove the gap in this case? Would be forever grateful!

Regards

Did you try with actions? I do something similar with move actions and works without problems. — Sebastián Castro
as @Setrio, i have no issues with this. Did you stop the scroll with the seam mid-screen to see if it exists in the absence of motion ? — YvesLeBorg
@Setrio Hmm, I not that good with actions actually, could you paste some sample code? It is the same principle? — Alouette
I've had this problem before and never managed to fix it. I moved my sprites using both actions and position updating - none worked. — Voldemort

Sebastián Castro Sebastián Castro · Accepted Answer · 2012-02-14T17:01:42

Here is some old code that i use to make clouds appears over an scene

Clouds.h

#import <Foundation/Foundation.h>
#import "cocos2d.h"

@interface Clouds : CCLayer {
    CCSprite *first;
    CCSprite *second;
    float firstX0;
    float secondX0;
    float firstXf;
    float secondXf;
    float height;
    float firstWidth;
    float secondWidth;
    float Yvalue;
    float duration;
    id moveFirstDone;
    id moveSecondDone;  
}

@end

Clouds.m

#import "Clouds.h"

@implementation Clouds
-(id) init{
    if( (self=[super init] )) {
        first = [CCSprite spriteWithFile:@"clouds_1.png"];
        firstWidth = first.contentSize.width;
        height = first.contentSize.height;
        second = [CCSprite spriteWithFile:@"clouds_2.png"];
        secondWidth = second.contentSize.width;
        Yvalue = 220.0f;
        duration = 200.0f;
        CGSize size = [[CCDirector sharedDirector] winSize];
        firstXf = -1 * (secondWidth - size.width + firstWidth/2);
        secondXf = -1 * (firstWidth + secondWidth/2);
        firstX0 = size.width + firstWidth/2;
        secondX0 = size.width + secondWidth/2;

        moveFirstDone = [CCCallFuncN actionWithTarget:self selector:@selector(callFirstDone:)];
        moveSecondDone = [CCCallFuncN actionWithTarget:self selector:@selector(callSecondDone:)];

        first.position = ccp(firstX0 + -1*firstX0,Yvalue);
        second.position = ccp(secondX0,Yvalue);
        [self addChild:first];
        [self addChild:second];
        [first runAction:[CCSequence actions:[CCMoveTo actionWithDuration:duration position:ccp(firstXf,Yvalue)],moveFirstDone,nil]];
        [second runAction:[CCSequence actions:[CCMoveTo actionWithDuration:duration*2 position:ccp(secondXf,Yvalue)],moveSecondDone,nil]];
    }
    return self;
}

-(void)callSecondDone:(id)sender{
    second.position = ccp(secondX0,Yvalue);
    [second runAction:[CCSequence actions:[CCMoveTo actionWithDuration:duration*2 position:ccp(secondXf,Yvalue)],moveSecondDone,nil]];
}

-(void)callFirstDone:(id)sender{
    first.position = ccp(firstX0,Yvalue);
    [first runAction:[CCSequence actions:[CCMoveTo actionWithDuration:duration*2 position:ccp(firstXf,Yvalue)],moveFirstDone,nil]];
}
@end

Using

    Clouds *clouds = [Clouds node];
    [self addChild: clouds z:0];

you add the node to your main layer/scene

I don't know if this is exactly what you need but maybe it helps. See a video of the effect that i get using this approach https://rapidshare.com/files/3478655240/2012-02-14_1458.swf

Cocos2D: Gap in scrolling background

2 Answers