这里用shader处理了像素，使黑色背景透明，直接上代码
ShaderSprite.h
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#ifndef __TestShader__ShaderSprite__
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#define __TestShader__ShaderSprite__
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#include "cocos2d.h"
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USING_NS_CC;
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class ShaderSprite : public CCSprite {
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public:
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static ShaderSprite* create(const char* pszFileName);
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virtual bool initWithTexture(CCTexture2D *pTexture, const CCRect& rect);
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virtual void draw(void);
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};
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#endif /* defined(__TestShader__ShaderSprite__) */
ShaderSprite.cpp
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#include "ShaderSprite.h"
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static CC_DLL const GLchar *transparentshader =
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#include "tansparentshader.h"
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ShaderSprite* ShaderSprite::create(const char *pszFileName)
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{
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ShaderSprite *pRet = new ShaderSprite();
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if (pRet && pRet->initWithFile(pszFileName)) {
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pRet->autorelease();
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return pRet;
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}
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else
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{
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delete pRet;
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pRet = NULL;
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return NULL;
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}
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}
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bool ShaderSprite::initWithTexture(CCTexture2D *pTexture, const CCRect& rect)
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{
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do{
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CC_BREAK_IF(!CCSprite::initWithTexture(pTexture, rect));
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m_pShaderProgram = new CCGLProgram();
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m_pShaderProgram ->initWithVertexShaderByteArray(ccPositionTextureA8Color_vert, transparentshader);
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CHECK_GL_ERROR_DEBUG();
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m_pShaderProgram->addAttribute(kCCAttributeNamePosition, kCCVertexAttrib_Position);
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m_pShaderProgram->addAttribute(kCCAttributeNameColor, kCCVertexAttrib_Color);
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m_pShaderProgram->addAttribute(kCCAttributeNameTexCoord, kCCVertexAttrib_TexCoords);
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CHECK_GL_ERROR_DEBUG();
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m_pShaderProgram->link();
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CHECK_GL_ERROR_DEBUG();
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m_pShaderProgram->updateUniforms();
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CHECK_GL_ERROR_DEBUG();
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return true;
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}while(0);
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return false;
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}
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void ShaderSprite::draw(void)
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{
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CC_PROFILER_START_CATEGORY(kCCProfilerCategorySprite, "CCSprite - draw");
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CCAssert(!m_pobBatchNode, "If CCSprite is being rendered by CCSpriteBatchNode, CCSprite#draw SHOULD NOT be called");
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CC_NODE_DRAW_SETUP();
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ccGLEnableVertexAttribs( kCCVertexAttribFlag_PosColorTex );
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ccGLBlendFunc(m_sBlendFunc.src, m_sBlendFunc.dst);
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m_pShaderProgram->use();
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m_pShaderProgram->setUniformsForBuiltins();
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ccGLBindTexture2D(m_pobTexture->getName());
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#define kQuadSize sizeof(m_sQuad.bl)
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long offset = (long)&m_sQuad;
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int diff = offsetof( ccV3F_C4B_T2F, vertices);
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glVertexAttribPointer(kCCVertexAttrib_Position, 3, GL_FLOAT, GL_FALSE, kQuadSize, (void*) (offset + diff));
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diff = offsetof( ccV3F_C4B_T2F, texCoords);
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glVertexAttribPointer(kCCVertexAttrib_TexCoords, 2, GL_FLOAT, GL_FALSE, kQuadSize, (void*)(offset + diff));
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diff = offsetof( ccV3F_C4B_T2F, colors);
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glVertexAttribPointer(kCCVertexAttrib_Color, 4, GL_UNSIGNED_BYTE, GL_TRUE, kQuadSize, (void*)(offset + diff));
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glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
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CHECK_GL_ERROR_DEBUG();
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CC_INCREMENT_GL_DRAWS(1);
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CC_PROFILER_STOP_CATEGORY(kCCProfilerCategorySprite, "CCSprite - draw");
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}
片段着色器代码
tansparentshader.h
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" \n\
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#ifdef GL_ES \n\
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precision lowp float; \n\
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#endif \n\
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varying vec4 v_fragmentColor; \n\
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varying vec2 v_texCoord; \n\
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uniform sampler2D u_texture; \n\
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void main() \n\
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{ \n\
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float ratio=0.0; \n\
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vec4 texColor = texture2D(u_texture, v_texCoord); \n\
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ratio = texColor[0] > texColor[1]?(texColor[0] > texColor[2] ? texColor[0] : texColor[2]) :(texColor[1] > texColor[2]? texColor[1] : texColor[2]); \n\
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if (ratio != 0.0) \n\
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{ \n\
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texColor[0] = texColor[0] / ratio; \n\
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texColor[1] = texColor[1] / ratio; \n\
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texColor[2] = texColor[2] / ratio; \n\
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texColor[3] = ratio; \n\
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} \n\
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else \n\
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{ \n\
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texColor[3] = 0.0; \n\
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} \n\
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gl_FragColor = v_fragmentColor*texColor; \n\
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}";
注意shader编程没有隐士数据类型转换，所以都显示为float了。
然后ratio是指在rgb中找最大的，假设ratio为0直接将alpha设为0，否则alpha设为ratio，然后各rgb除以ratio，这里是为了做渐变，否则变化太生硬。
上图：
好了，上面两张图是一样的。仅仅是屏幕背景一个是白色，一个是黑色。图片背景透明了。
