I've written a class which makes masking in Cocos2D fairly easy.
You just have to define an object and a mask. And that's it!
Insert this class into your project:
The h file
//
// CCMask.h
// Masking
//
// Created by Gilles Lesire on 22/04/11.
// Copyright 2011 iCapps. All rights reserved.
//
#import "cocos2d.h"
@interface CCMask : CCSprite {
// Some screen information
CGSize size;
CGPoint screenMid;
// The given sprites
CCSprite *maskSprite;
CCSprite *objectSprite;
// RenderTextures use for masking
CCRenderTexture *maskNegative;
CCRenderTexture *masked;
}
// Initialize a masked object based on an object sprite and a mask sprite
+ (id) createMaskForObject: (CCSprite *) object withMask: (CCSprite *) mask;
// Redraw the masked image
- (void) redrawMasked;
// When dynamic masking is active, you have the ability to change the masked object or the mask itself
- (void) setObject: (CCSprite *) object;
- (void) setMask: (CCSprite *) mask;
// Return the masked object as a sprite
- (CCSprite *) getMaskedSprite;
@endThe m file
//
// CCMask.m
// Masking
//
// Created by Gilles Lesire on 22/04/11.
// Copyright 2011 iCapps. All rights reserved.
//
#import "CCMask.h"
@interface CCMask(Private)
- (id) initWithObject: (CCSprite *) object mask: (CCSprite *) mask;
- (void) resetObject;
- (void) mask;
@end
@implementation CCMask
+ (id) createMaskForObject: (CCSprite *) object withMask: (CCSprite *) mask {
return [[[self alloc] initWithObject: object mask: mask] autorelease];
}
- (id) initWithObject: (CCSprite *) object mask: (CCSprite *) mask {
NSAssert(object != nil, @"Invalid sprite for object");
NSAssert(mask != nil, @"Invalid sprite for mask");
if((self = [super init])) {
[self setObject: object];
[self setMask: mask];
// Get window size, we want masking over entire screen don't we?
size = [[CCDirector sharedDirector] winSize];
// Create point with middle of screen
screenMid = ccp(size.width * 0.5f, size.height * 0.5f);
// Create the rendureTextures to create cut outs
maskNegative = [CCRenderTexture renderTextureWithWidth: size.width height: size.height];
masked = [CCRenderTexture renderTextureWithWidth: size.width height: size.height];
// Set render textures at middle of screen
maskNegative.position = screenMid;
masked.position = screenMid;
// Set correct alpha channel for textures
[[maskNegative sprite] setBlendFunc: (ccBlendFunc) { GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA }];
[[masked sprite] setBlendFunc: (ccBlendFunc) { GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA }];
// Load object into RenderTextures
[self resetObject];
// Mask the object
[self mask];
// Add the masked object to the screen
[self addChild: masked];
}
return self;
}
- (void) resetObject {
// Clear textures first
[maskNegative clear:0 g:0 b:0 a:1.0];
[masked clear:0 g:0 b:0 a:1.0];
// Begin action for cut out
[maskNegative begin];
// Load sprite
[objectSprite visit];
// End loading sprites
[maskNegative end];
// Begin action for masked
[masked begin];
// Load sprite
[objectSprite visit];
// End loading sprites
[masked end];
}
- (void) redrawMasked {
// Put object back on the screen
[self resetObject];
// Cut out the parts we don't want to see
[self mask];
}
- (void) mask {
// Set up the burn sprite that will "knock out" parts of the darkness layer depending on the alpha value of the pixels in the image.
[maskSprite setBlendFunc: (ccBlendFunc) { GL_ZERO, GL_ONE_MINUS_SRC_ALPHA }];
[maskSprite retain];
// Start cutting out the parts we want to show
[maskNegative begin];
// Limit drawing to the alpha channel
glColorMask(0.0f, 0.0f, 0.0f, 1.0f);
// Draw
[maskSprite visit];
// Reset color mask
glColorMask(1.0f, 1.0f, 1.0f, 1.0f);
[maskNegative end];
[self addChild: maskNegative];
// Create a temporary mask of the left cut out
CCSprite *maskCut = maskNegative.sprite;
maskCut.position = screenMid;
// Set up the burn sprite that will "knock out" parts of the darkness layer depending on the alpha value of the pixels in the image.
[maskCut setBlendFunc: (ccBlendFunc) { GL_ZERO, GL_ONE_MINUS_SRC_ALPHA }];
[maskCut retain];
[masked begin];
// Limit drawing to the alpha channel
glColorMask(0.0f, 0.0f, 0.0f, 1.0f);
// Draw
[maskCut visit];
// Reset color mask
glColorMask(1.0f, 1.0f, 1.0f, 1.0f);
[masked end];
}
- (void) setObject: (CCSprite *) object {
objectSprite = object;
}
- (void) setMask: (CCSprite *) mask {
maskSprite = mask;
}
- (CCSprite *) getMaskedSprite {
return masked.sprite;
}
- (void) dealloc {
[super dealloc];
}
@endHow to use it
Import the CCMask in the file (of course)
// Ask director the the window size
CGSize size = [[CCDirector sharedDirector] winSize];
// Create an object and a mask
object = [CCSprite spriteWithFile:@"Ball.png"];
mask = [CCSprite spriteWithFile:@"star.png"];
// Set their positions
object.position = ccp(size.width * 0.5f, size.height * 0.5f + 310);
mask.position = ccp(size.width * 0.5f, size.height * 0.5f + 310);
// Create a masked image based on the object and the mask and add it to the screen
CCMask *masked = [CCMask createMaskForObject: object withMask: mask];
[self addChild: masked];You can also use redrawMasked is you feel the urge to rerender the mask, for example after you moved it.
[masked redrawMasked];
