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我正在使用下面的代碼來關閉紋理。但我不知道如何檢測劃傷紋理的百分比..例如，當用戶劃傷80％時，它應該淡出。誰能幫我這個？cocos2d - 讀取CCRenderTexture的數據
-(id) init
{
if((self=[super init]))
{
CGSize size = [[CCDirector sharedDirector] winSize];
[self setIsTouchEnabled:YES];
reset = YES;
bg = [CCSprite spriteWithFile:@"background.png"];
bg.position = ccp(size.width /2 , size.height/2);
[self addChild:bg z:1];
burnSprite = [CCSprite spriteWithFile:@"fire.png"];
[burnSprite setBlendFunc:(ccBlendFunc) { GL_ZERO, GL_ONE_MINUS_SRC_ALPHA }];
[burnSprite retain];
burnSprite.scale = 0.7f;
// Scratch Background
scratchBg = [[CCSprite spriteWithFile:@"scratchBg.png"] retain];
scratchBg.position = ccp(size.width/2, size.height/2);
// Scratch Layer
scratchLayer = [CCRenderTexture renderTextureWithWidth:size.width height:size.height];
scratchLayer.position = ccp(size.width/2 , size.height/2);
[[scratchLayer sprite] setBlendFunc: (ccBlendFunc) { GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA }];
[self addChild:scratchLayer z:2];
[self schedule: @selector(tick:)];
}
return self;
}
- (void) drawTexture
{
// Update the render texture
[scratchLayer begin];
// Limit drawing to the alpha channel
glColorMask(0.0f, 0.0f, 0.0f, 1.0f);
// Draw
[burnSprite visit];
// Reset color mask
glColorMask(1.0f, 1.0f, 1.0f, 1.0f);
[scratchLayer end];
}