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

    // texCoods
    diff = offsetof( ccV3F_C4B_T2F, texCoords);
    glVertexAttribPointer(kCCVertexAttrib_TexCoords, , GL_FLOAT, GL_FALSE, kQuadSize, (void*)(offset + diff));

    // color
    diff = offsetof( ccV3F_C4B_T2F, colors);
    glVertexAttribPointer(kCCVertexAttrib_Color, , GL_UNSIGNED_BYTE, GL_TRUE, kQuadSize, (void*)(offset + diff));

    glDrawArrays(GL_TRIANGLE_STRIP, , );

    CHECK_GL_ERROR_DEBUG();

    CC_INCREMENT_GL_DRAWS();
    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[] > texColor[]?(texColor[] > texColor[] ? texColor[] : texColor[]) :(texColor[] > texColor[]? texColor[] : texColor[]);                                      \n\
if (ratio != 0.0)                                          \n\
{                                                          \n\
    texColor[] = texColor[] /  ratio;                    \n\
    texColor[] = texColor[] /  ratio;                    \n\
    texColor[] = texColor[] /  ratio;                    \n\
    texColor[] = ratio;                                   \n\
}                                                          \n\
else                                                       \n\
{                                                          \n\
    texColor[] = 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。