Cocos2d: Working with Sprites

0
268
5 min read

 

(For more resources on Cocos2d, see here.)

 

Drawing sprites

The most fundamental task in 2D game development is drawing a sprite. Cocos2d provides the user with a lot of flexibility in this area. In this recipe we will cover drawing sprites using CCSprite, spritesheets, CCSpriteFrameCache, and CCSpriteBatchNode. We will also go over mipmapping. In this recipe we see a scene with Alice from Through The Looking Glass.

Cocos2d for iPhone 1 Game Development Cookbook

Getting ready

Please refer to the project RecipeCollection01 for the full working code of this recipe.

How to do it…

Execute the following code:

@implementation Ch1_DrawingSprites
-(CCLayer*) runRecipe {
/*** Draw a sprite using CCSprite ***/
CCSprite *tree1 = [CCSprite spriteWithFile:@"tree.png"];

//Position the sprite using the tree base as a guide (y anchor
point = 0)
[tree1 setPosition:ccp(20,20)];
tree1.anchorPoint = ccp(0.5f,0);
[tree1 setScale:1.5f];
[self addChild:tree1 z:2 tag:TAG_TREE_SPRITE_1];

/*** Load a set of spriteframes from a PLIST file and draw one by
name ***/

//Get the sprite frame cache singleton
CCSpriteFrameCache *cache = [CCSpriteFrameCache
sharedSpriteFrameCache];

//Load our scene sprites from a spritesheet
[cache addSpriteFramesWithFile:@"alice_scene_sheet.plist"];

//Specify the sprite frame and load it into a CCSprite
CCSprite *alice = [CCSprite spriteWithSpriteFrameName:@"alice.png"];

//Generate Mip Maps for the sprite
[alice.texture generateMipmap];
ccTexParams texParams = { GL_LINEAR_MIPMAP_LINEAR, GL_LINEAR, GL_
CLAMP_TO_EDGE, GL_CLAMP_TO_EDGE };
[alice.texture setTexParameters:&texParams];

//Set other information.
[alice setPosition:ccp(120,20)];
[alice setScale:0.4f];
alice.anchorPoint = ccp(0.5f,0);

//Add Alice with a zOrder of 2 so she appears in front of other
sprites
[self addChild:alice z:2 tag:TAG_ALICE_SPRITE];

//Make Alice grow and shrink.
[alice runAction: [CCRepeatForever actionWithAction:
[CCSequence actions:[CCScaleTo actionWithDuration:4.0f scale
:0.7f], [CCScaleTo actionWithDuration:4.0f scale:0.1f], nil] ] ];

/*** Draw a sprite CGImageRef ***/
UIImage *uiImage = [UIImage imageNamed: @"cheshire_cat.png"];
CGImageRef imageRef = [uiImage CGImage];
CCSprite *cat = [CCSprite spriteWithCGImage:imageRef key:@
"cheshire_cat.png"];
[cat setPosition:ccp(250,180)];
[cat setScale:0.4f];
[self addChild:cat z:3 tag:TAG_CAT_SPRITE];

/*** Draw a sprite using CCTexture2D ***/
CCTexture2D *texture = [[CCTextureCache sharedTextureCache]addImage:@"tree.png"];
CCSprite *tree2 = [CCSprite spriteWithTexture:texture];
[tree2 setPosition:ccp(300,20)];
tree2.anchorPoint = ccp(0.5f,0);
[tree2 setScale:2.0f];
[self addChild:tree2 z:2 tag:TAG_TREE_SPRITE_2];

/*** Draw a sprite using CCSpriteFrameCache and CCTexture2D ***/
CCSpriteFrame *frame = [CCSpriteFrame frameWithTexture:texture
rect:tree2.textureRect];
[[CCSpriteFrameCache sharedSpriteFrameCache] addSpriteFrame:
frame name:@"tree.png"];
CCSprite *tree3 = [CCSprite spriteWithSpriteFrame:[[CCSpriteFrame
Cache sharedSpriteFrameCache] spriteFrameByName:@"tree.png"]];
[tree3 setPosition:ccp(400,20)];
tree3.anchorPoint = ccp(0.5f,0);
[tree3 setScale:1.25f];
[self addChild:tree3 z:2 tag:TAG_TREE_SPRITE_3];

/*** Draw sprites using CCBatchSpriteNode ***/

//Clouds
CCSpriteBatchNode *cloudBatch = [CCSpriteBatchNode
batchNodeWithFile:@"cloud_01.png" capacity:10];
[self addChild:cloudBatch z:1 tag:TAG_CLOUD_BATCH];
for(int x=0; x<10; x++){
CCSprite *s = [CCSprite spriteWithBatchNode:cloudBatch
rect:CGRectMake(0,0,64,64)];
[s setOpacity:100];
[cloudBatch addChild:s];
[s setPosition:ccp(arc4random()%500-50, arc4random()%150+200)];
}

//Middleground Grass
int capacity = 10;
CCSpriteBatchNode *grassBatch1 = [CCSpriteBatchNode
batchNodeWithFile:@"grass_01.png" capacity:capacity];
[self addChild:grassBatch1 z:1 tag:TAG_GRASS_BATCH_1];
for(int x=0; x<capacity; x++){
CCSprite *s = [CCSprite spriteWithBatchNode:grassBatch1
rect:CGRectMake(0,0,64,64)];
[s setOpacity:255];
[grassBatch1 addChild:s];
[s setPosition:ccp(arc4random()%500-50, arc4random()%20+70)];
}

//Foreground Grass
CCSpriteBatchNode *grassBatch2 = [CCSpriteBatchNode
batchNodeWithFile:@"grass_01.png" capacity:10];
[self addChild:grassBatch2 z:3 tag:TAG_GRASS_BATCH_2];
for(int x=0; x<30; x++){
CCSprite *s = [CCSprite spriteWithBatchNode:grassBatch2
rect:CGRectMake(0,0,64,64)];
[s setOpacity:255];
[grassBatch2 addChild:s];
[s setPosition:ccp(arc4random()%500-50, arc4random()%40-10)];
}

/*** Draw colored rectangles using a 1px x 1px white texture ***/

//Draw the sky using blank.png
[self drawColoredSpriteAt:ccp(240,190) withRect:CGRectMa
ke(0,0,480,260) withColor:ccc3(150,200,200) withZ:0];

//Draw the ground using blank.png
[self drawColoredSpriteAt:ccp(240,30)
withRect:CGRectMake(0,0,480,60) withColor:ccc3(80,50,25) withZ:0];

return self;
}

-(void) drawColoredSpriteAt:(CGPoint)position withRect:(CGRect)rect
withColor:(ccColor3B)color withZ:(float)z {
CCSprite *sprite = [CCSprite spriteWithFile:@"blank.png"];
[sprite setPosition:position];
[sprite setTextureRect:rect];
[sprite setColor:color];
[self addChild:sprite];

//Set Z Order
[self reorderChild:sprite z:z];
}

@end

How it works…

This recipe takes us through most of the common ways of drawing sprites:

  • Creating a CCSprite from a file:
    First, we have the simplest way to draw a sprite. This involves using the CCSprite class method as follows:
    +(id)spriteWithFile:(NSString*)filename;

    This is the most straightforward way to initialize a sprite and is adequate for many situations.

  • Other ways to load a sprite from a file:
    After this, we will see examples of CCSprite creation using UIImage/CGImageRef, CCTexture2D, and a CCSpriteFrame instantiated using a CCTexture2D object. CGImageRef support allows you to tie Cocos2d into other frameworks and toolsets. CCTexture2D is the underlying mechanism for texture creation.
  • Loading spritesheets using CCSpriteFrameCache:
    Next, we will see the most powerful way to use sprites, the CCSpriteFrameCache class. Introduced in Cocos2d-iPhone v0.99, the CCSpriteFrameCache singleton is a cache of all sprite frames. Using a spritesheet and its associated PLIST file we can load multiple sprites into the cache. From here we can create CCSprite objects with sprites from the cache:
    +(id)spriteWithSpriteFrameName:(NSString*)filename;
  • Mipmapping:
    Mipmapping allows you to scale a texture or to zoom in or out of a scene without aliasing your sprites. When we scale Alice down to a small size, aliasing will inevitably occur. With mipmapping turned on, Cocos2d dynamically generates lower resolution textures to smooth out any pixelation at smaller scales. Go ahead and comment out the following lines:

    [alice.texture generateMipmap];
    ccTexParams texParams = { GL_LINEAR_MIPMAP_LINEAR, GL_LINEAR,
    GL_CLAMP_TO_EDGE, GL_CLAMP_TO_EDGE };
    [alice.texture setTexParameters:&texParams];

    Now you should see this pixelation as Alice gets smaller.

  • Drawing many derivative sprites with CCSpriteBatchNode:
    The CCSpriteBatchNode class, added in v0.99.5, introduces an efficient way to draw and re-draw the same sprite over and over again. A batch node is created with the following method:
    CCSpriteBatchNode *cloudBatch = [CCSpriteBatchNode
    batchNodeWithFile:@"cloud_01.png" capacity:10];

    Then, you create as many sprites as you want using the follow code:

    CCSprite *s = [CCSprite spriteWithBatchNode:cloudBatch
    rect:CGRectMake(0,0,64,64)];
    [cloudBatch addChild:s];

    Setting the capacity to the number of sprites you plan to draw tells Cocos2d to allocate that much space. This is yet another tweak for extra efficiency, though it is not absolutely necessary that you do this. In these three examples we draw 10 randomly placed clouds and 60 randomly placed bits of grass.

  • Drawing colored rectangles:
    Finally, we have a fairly simple technique that has a variety of uses. By drawing a sprite with a blank 1px by 1px white texture and then coloring it and setting its textureRect property we can create very useful colored bars:
    CCSprite *sprite = [CCSprite spriteWithFile:@"blank.png"];
    [sprite setTextureRect:CGRectMake(0,0,480,320)];
    [sprite setColor:ccc3(255,128,0)];

    In this example we have used this technique to create very simple ground and sky backgrounds.

 


Subscribe to the weekly Packt Hub newsletter

* indicates required

LEAVE A REPLY

Please enter your comment!
Please enter your name here