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看了下实现，基本有了办法。CCSprite是在initWithTexture的时候渲染的贴图，如果在这里面设置一个一个灰度Shader，也许可以将图片改成灰白色。

GL Shader脚本代码：

#ifdef GL_ES
precision mediump float;
#endif
uniform sampler2D u_texture;
varying vec2 v_texCoord;
varying vec4 v_fragmentColor;
void main(void)
{
// Convert to greyscale using NTSC weightings
float alpha = texture2D(u_texture, v_texCoord).a;
float grey = dot(texture2D(u_texture, v_texCoord).rgb, vec3(0.299, 0.587, 0.114));
gl_FragColor = vec4(grey, grey, grey, alpha);
}

Google了下，vec3(0.299, 0.587, 0.114) 是RGB转YUV的参数值。

计算完了之后根据原来的纹理alpha值，输出我们处理后的颜色到gl_FragColor，就可以让shader去渲染黑白图。

里面主要是在光栅化后的片段进行颜色处理，最后输出的是像素，它不会产生额外纹理，所以不会卡。

注意：GLSL1.0的可能有些函数不支持，会crash。不过目前基本可以不考虑。

下面就是我写好的类，加入自己的工程就可以了。

头文件

//
// BYGraySprite.h
// Demo
//
// Created by Yanghui Liu on 12-11-2.
// Copyright (c) 2012年 BoyoJoy. All rights reserved.
//#ifndef Demo_BYGraySprite_h
#define Demo_BYGraySprite_h#include "cocoa/CCGeometry.h"
#include "cocos2d.h"
USING_NS_CC;class BYGraySprite : public CCSprite{public:BYGraySprite();virtual ~BYGraySprite();static BYGraySprite* create(const char* pszFileName);bool initWithTexture(CCTexture2D* pTexture, const CCRect& tRect);virtual void draw();};#endif

//
// BYGraySprite.cpp
// Demo
//
// Created by Yanghui Liu on 12-11-2.
// Copyright (c) 2012年 BoyoJoy. All rights reserved.
//#include "BYGraySprite.h"BYGraySprite::BYGraySprite(){}BYGraySprite::~BYGraySprite(){}BYGraySprite* BYGraySprite::create( const char* pszFileName ){BYGraySprite* graySprite = new BYGraySprite;if (graySprite && graySprite->initWithFile(pszFileName)){graySprite->autorelease();return graySprite;}else{CC_SAFE_RELEASE(graySprite);return NULL;}
}bool BYGraySprite::initWithTexture(CCTexture2D* pTexture, const CCRect& tRect ){do{CC_BREAK_IF(!CCSprite::initWithTexture(pTexture, tRect));GLchar* pszFragSource ="#ifdef GL_ES \n \precision mediump float; \n \#endif \n \uniform sampler2D u_texture; \n \varying vec2 v_texCoord; \n \varying vec4 v_fragmentColor; \n \void main(void) \n \{ \n \// Convert to greyscale using NTSC weightings \n \float grey = dot(texture2D(u_texture, v_texCoord).rgb, vec3(0.299, 0.587, 0.114)); \n \gl_FragColor = vec4(grey, grey, grey, 1.0); \n \}";CCGLProgram* pProgram = new CCGLProgram();pProgram->initWithVertexShaderByteArray(ccPositionTextureColor_vert, pszFragSource);this->setShaderProgram(pProgram);pProgram->release();CHECK_GL_ERROR_DEBUG();this->getShaderProgram()->addAttribute(kCCAttributeNamePosition, kCCVertexAttrib_Position);this->getShaderProgram()->addAttribute(kCCAttributeNameColor, kCCVertexAttrib_Color);this->getShaderProgram()->addAttribute(kCCAttributeNameTexCoord, kCCVertexAttrib_TexCoords);CHECK_GL_ERROR_DEBUG();this->getShaderProgram()->link();CHECK_GL_ERROR_DEBUG();this->getShaderProgram()->updateUniforms();CHECK_GL_ERROR_DEBUG();return true;} while (0);return false;
}void BYGraySprite::draw(){ccGLEnableVertexAttribs(kCCVertexAttribFlag_PosColorTex );ccGLBlendFunc( m_sBlendFunc.src, m_sBlendFunc.dst );this->getShaderProgram()->use();this->getShaderProgram()->setUniformForModelViewProjectionMatrix();ccGLBindTexture2D( this->getTexture()->getName() );#define kQuadSize sizeof(m_sQuad.bl)long offset = (long)&m_sQuad;// vertexint diff = offsetof( ccV3F_C4B_T2F, vertices);glVertexAttribPointer(kCCVertexAttrib_Position, 3, GL_FLOAT, GL_FALSE, kQuadSize, (void*) (offset + diff));// texCoodsdiff = offsetof( ccV3F_C4B_T2F, texCoords);glVertexAttribPointer(kCCVertexAttrib_TexCoords, 2, GL_FLOAT, GL_FALSE, kQuadSize, (void*)(offset + diff));// colordiff = offsetof( ccV3F_C4B_T2F, colors);glVertexAttribPointer(kCCVertexAttrib_Color, 4, GL_UNSIGNED_BYTE, GL_TRUE, kQuadSize, (void*)(offset + diff));glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);CC_INCREMENT_GL_DRAWS(1);
}

BYGraySprite* graySprite = BYGraySprite::create("Icon.png");graySprite->setPosition( ccp(size.width/2, size.height/2) );this->addChild(graySprite);

2012.11.14更新

二、之前alpha值是直接用的1，所以透明图会渲染成黑色。把原来纹理的alpha取出来并使用。就可以避免该问题。

也就是将GL脚本代码中的

float grey = dot(texture2D(u_texture, v_texCoord).rgb, vec3(0.299, 0.587, 0.114)); \n \

gl_FragColor = vec4(grey, grey, grey, 1.0); \n \

改成:

vec4 col = texture2D(u_texture, v_texCoord); \n \

float grey = dot(col.rgb, vec3(0.299, 0.587, 0.114)); \n \

gl_FragColor = vec4(grey, grey, grey, col.a); \n \

这里感谢网友whitespace，发现该问题。并留言提供方法。