用shader使图片背景透明

转自：http://blog.csdn.net/dawn_moon/article/details/8631783

好吧，终于抽时间写这篇文章了。

手头上有很多人物行走图，技能特效图等，但这些图都有个纯黑色背景，怎么样将内容显示出来，让背景透明呢？前段时间搞了一下，感谢群里的童鞋们，提供了思路和方法。

 

这里用shader处理了像素，使黑色背景透明，直接上代码

ShaderSprite.h

#ifndef __TestShader__ShaderSprite__

#define __TestShader__ShaderSprite__



#include "cocos2d.h"

USING_NS_CC;



class ShaderSprite : public CCSprite {

    

public:

    static ShaderSprite* create(const char* pszFileName);

    virtual bool initWithTexture(CCTexture2D *pTexture, const CCRect& rect);

    virtual void draw(void);

};



#endif /* defined(__TestShader__ShaderSprite__) */

ShaderSprite.cpp

#include "ShaderSprite.h"



static CC_DLL const GLchar *transparentshader =

#include "tansparentshader.h"



ShaderSprite* ShaderSprite::create(const char *pszFileName)

{

    ShaderSprite *pRet = new ShaderSprite();

    if (pRet && pRet->initWithFile(pszFileName)) {

        pRet->autorelease();

        return pRet;

    }

    else

    {

        delete pRet;

        pRet = NULL;

        return NULL;

    }

}



bool ShaderSprite::initWithTexture(CCTexture2D *pTexture, const CCRect& rect)

{

    do{

//        CCLog("override initWithTexture!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!");

        CC_BREAK_IF(!CCSprite::initWithTexture(pTexture, rect));

        

        // 加载顶点着色器和片元着色器

        m_pShaderProgram = new  CCGLProgram();

        m_pShaderProgram ->initWithVertexShaderByteArray(ccPositionTextureA8Color_vert, transparentshader);

        

        CHECK_GL_ERROR_DEBUG();

        

        // 启用顶点着色器的attribute变量，坐标、纹理坐标、颜色

        m_pShaderProgram->addAttribute(kCCAttributeNamePosition, kCCVertexAttrib_Position);

        m_pShaderProgram->addAttribute(kCCAttributeNameColor, kCCVertexAttrib_Color);

        m_pShaderProgram->addAttribute(kCCAttributeNameTexCoord, kCCVertexAttrib_TexCoords);

        

        CHECK_GL_ERROR_DEBUG();

        

        // 自定义着色器链接

        m_pShaderProgram->link();

        

        CHECK_GL_ERROR_DEBUG();

        

        // 设置移动、缩放、旋转矩阵

        m_pShaderProgram->updateUniforms();

        

        CHECK_GL_ERROR_DEBUG();

        

        return true;

        

    }while(0);

    return false;

}



void ShaderSprite::draw(void)

{

//    CCLog("override draw!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!");

    CC_PROFILER_START_CATEGORY(kCCProfilerCategorySprite, "CCSprite - draw");

    

    CCAssert(!m_pobBatchNode, "If CCSprite is being rendered by CCSpriteBatchNode, CCSprite#draw SHOULD NOT be called");

    

    CC_NODE_DRAW_SETUP();

    

    //

    // 启用attributes变量输入，顶点坐标，纹理坐标，颜色

    //

    ccGLEnableVertexAttribs( kCCVertexAttribFlag_PosColorTex );

    ccGLBlendFunc(m_sBlendFunc.src, m_sBlendFunc.dst);

    

    m_pShaderProgram->use();

    m_pShaderProgram->setUniformsForBuiltins();

    

    // 绑定纹理到纹理槽0

    ccGLBindTexture2D(m_pobTexture->getName());





    

#define kQuadSize sizeof(m_sQuad.bl)

    long offset = (long)&m_sQuad;

    

    // vertex

    int diff = offsetof( ccV3F_C4B_T2F, vertices);

    glVertexAttribPointer(kCCVertexAttrib_Position, 3, GL_FLOAT, GL_FALSE, kQuadSize, (void*) (offset + diff));

    

    // texCoods

    diff = offsetof( ccV3F_C4B_T2F, texCoords);

    glVertexAttribPointer(kCCVertexAttrib_TexCoords, 2, GL_FLOAT, GL_FALSE, kQuadSize, (void*)(offset + diff));

    

    // color

    diff = offsetof( ccV3F_C4B_T2F, colors);

    glVertexAttribPointer(kCCVertexAttrib_Color, 4, GL_UNSIGNED_BYTE, GL_TRUE, kQuadSize, (void*)(offset + diff));

    

    

    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

    

    CHECK_GL_ERROR_DEBUG();



    CC_INCREMENT_GL_DRAWS(1);

    CC_PROFILER_STOP_CATEGORY(kCCProfilerCategorySprite, "CCSprite - draw");

}

片段着色器代码

 

tansparentshader.h

"                                                       \n\

#ifdef GL_ES                                            \n\

precision lowp float;                                   \n\

#endif                                                  \n\

varying vec4 v_fragmentColor;                           \n\

varying vec2 v_texCoord;                                \n\

uniform sampler2D u_texture;                            \n\

void main()                                             \n\

{                                                       \n\

    float ratio=0.0;                                    \n\

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

    ratio = texColor[0] > texColor[1]?(texColor[0] > texColor[2] ? texColor[0] : texColor[2]) :(texColor[1] > texColor[2]? texColor[1] : texColor[2]);                                      \n\

if (ratio != 0.0)                                          \n\

{                                                          \n\

    texColor[0] = texColor[0] /  ratio;                    \n\

    texColor[1] = texColor[1] /  ratio;                    \n\

    texColor[2] = texColor[2] /  ratio;                    \n\

    texColor[3] = ratio;                                   \n\

}                                                          \n\

else                                                       \n\

{                                                          \n\

    texColor[3] = 0.0;                                     \n\

}                                                          \n\

gl_FragColor = v_fragmentColor*texColor;                   \n\

}";

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，如果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。只是屏幕背景一个是白色，一个是黑色。图片背景透明了。