一、目的
Cocos2d-x做项目时经常会碰到要对图片进行变色的需求，最常用的就是变灰了，就要让按钮变灰来表示当前的状态是不可点的。 但是Cocos2d-x的Sprite中是没有这个变灰支持的。那么，就要我们自己动手来扩展实现一个。我们让这个带变色功能的Sprite叫做FilterSprite。这个FilterSprite扩展了Sprite的功能：可以方便地变换颜色。
二、原理
对图片进行颜色变换，就是对图片上的每个像素进行变换。要实现这个，要新创建一个fragmentShader，这个fragmentShader 比sprite的那个fragmentShader多了一个颜色变换矩阵。shader会让图片上每个像素与颜色变换矩阵进行相乘，输出新的像素值。
这个shader是这样的：
#ifdef GL_ES
precision mediump float;
#endif
uniform sampler2D u_texture;
varying vec2 v_texCoord;
varying vec4 v_fragmentColor;
uniform mat4 fiterMat;
void main(void)
{
vec4 value = v_fragmentColor*texture2D(u_texture, v_texCoord);
gl_FragColor = fiterMat*value;
};
从shader上我们看到，“filterMat” 就是所谓的颜色变换矩阵，仅仅在原来像素输出前用它处理了一下：与待输出像素相乘。 这个shader是opengl层级的，要应用到coco2dx引擎中，我们要着手实现cocos2dx的FilterSprite类了。
三、实现
实现这个FilterSprite注意几个要点：
引擎中一个shader对应一个GLProgram，所以这个带颜色滤镜的shader（称为filterShader）对应一个GLProgram（称为filterProgram）对象，在实际使用时，是用对GLProgram进行了封装的GLProgramState（称为filterProgramState）对象，FilterSprite对象的_glProgramState要设置成filterProgramState对象，在源码中FilterSprite的initWithTexture进行这个filterShader和filterProgram的关联。
在渲染时要将滤镜传递给shader程序，在源码中就是在onDraw回调时调用：
glProgramState->setUniformMat4( “fiterMat”,m_uSpriteFilter)
四、使用
使用起来非常简单，只需要设置一个颜色矩阵，例如，如果要变灰就设置一个灰度矩阵，如果要恢复原貌就设置一个单位矩阵。
Sprite *_sprite1;
_sprite1 = FilterSprite::create(“Images/background3.png”);
GLfloat filterMat[16]= {
0.3f, 0.3f, 0.3f, 0.0f,
0.59f, 0.59f, 0.59f, 0.59f,
0.11f, 0.11f, 0.11f, 0.0f,
0.0f, 0.0f, 0.0f, 1.0f,
};
dynamic_cast(_sprite1)->setFilterMat(filterMat);
五、源码
FilterSprite.h:
/****************************************************************************
FilterSpirte.h
Created by LiaoYanXuan on 14-10-21.
****************************************************************************/
#ifndef __FilterSpirte_h
#define __FilterSpirte_h
#include “cocos2d.h”
USING_NS_CC;
class FilterSprite : public Sprite{
public:
FilterSprite();
virtual ~FilterSprite();
static FilterSprite* create();
static FilterSprite* create(const std::string& filename);
static FilterSprite* create(const std::string& filename, const Rect& rect);
static FilterSprite* createWithTexture(Texture2D *pTexture);
static FilterSprite* createWithTexture(Texture2D *pTexture, const Rect& rect, bool rotated=false);
static FilterSprite* createWithSpriteFrame(SpriteFrame *pSpriteFrame);
static FilterSprite* createWithSpriteFrameName(const std::string& spriteFrameName);
bool initWithTexture(Texture2D* pTexture, const Rect& tRect);
virtual void draw(Renderer *renderer, const Mat4 &transform, uint32_t flags) override;
void onDraw(const Mat4 &transform, uint32_t flags);
void setFilterMat(cocos2d::Mat4 matrixArray);
//to-do 提供一个设置滤镜的方法
protected:
CustomCommand _customCommand;
private:
cocos2d::Mat4 m_uSpriteFilter;
};
#endif
FilterSprite.cpp:
/****************************************************************************
FilterSpirte.h
Created by LiaoYanXuan on 14-10-21.
****************************************************************************/
#include “FilterSprite.h”
FilterSprite::FilterSprite(void)
{
m_uSpriteFilter=Mat4::IDENTITY;
}
FilterSprite::~FilterSprite()
{
}
FilterSprite* FilterSprite::create()
{
FilterSprite *sprite = new (std::nothrow) FilterSprite();
if (sprite && sprite->init())
{
sprite->autorelease();
return sprite;
}
CC_SAFE_DELETE(sprite);
return nullptr;
}
FilterSprite* FilterSprite::create(const std::string& filename)
{
FilterSprite *sprite = new (std::nothrow) FilterSprite();
if (sprite && sprite->initWithFile(filename))
{
sprite->autorelease();
return sprite;
}
CC_SAFE_DELETE(sprite);
return nullptr;
}
FilterSprite* FilterSprite::create(const std::string& filename, const Rect& rect)
{
FilterSprite *sprite = new (std::nothrow) FilterSprite();
if (sprite && sprite->initWithFile(filename, rect))
{
sprite->autorelease();
return sprite;
}
CC_SAFE_DELETE(sprite);
return nullptr;
}
FilterSprite* FilterSprite::createWithTexture(Texture2D *pTexture)
{
FilterSprite *sprite = new (std::nothrow) FilterSprite();
Rect rect = Rect::ZERO;
rect.size = pTexture->getContentSize();
if (sprite && sprite->initWithTexture(pTexture,rect))
{
sprite->autorelease();
return sprite;
}
CC_SAFE_DELETE(sprite);
return nullptr;
}
FilterSprite* FilterSprite::createWithTexture(Texture2D *texture, const Rect& rect, bool rotated)
{
FilterSprite *sprite = new (std::nothrow) FilterSprite();
if (sprite && sprite->initWithTexture(texture, rect))
{
sprite->autorelease();
return sprite;
}
CC_SAFE_DELETE(sprite);
return nullptr;
}
FilterSprite* FilterSprite::createWithSpriteFrame(SpriteFrame *spriteFrame)
{
FilterSprite *sprite = new (std::nothrow) FilterSprite();
if (sprite && spriteFrame && sprite->initWithSpriteFrame(spriteFrame))
{
sprite->autorelease();
return sprite;
}
CC_SAFE_DELETE(sprite);
return nullptr;
}
FilterSprite* FilterSprite::createWithSpriteFrameName(const std::string& spriteFrameName)
{
SpriteFrame *frame = SpriteFrameCache::getInstance()->getSpriteFrameByName(spriteFrameName);
#if COCOS2D_DEBUG > 0
char msg[256] = {0};
sprintf(msg, “Invalid spriteFrameName: %s”, spriteFrameName.c_str());
CCASSERT(frame != nullptr, msg);
#endif
return createWithSpriteFrame(frame);
}
bool FilterSprite::initWithTexture(Texture2D* pTexture, const Rect& tRect){
do{
CC_BREAK_IF(!Sprite::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 \
uniform mat4 fiterMat; \n \
void main(void) \n \
{ \n \
vec4 value = v_fragmentColor*texture2D(u_texture, v_texCoord); \n \
gl_FragColor = fiterMat*value; \n \
}”;
auto glprogram = GLProgram::createWithByteArrays(ccPositionTextureColor_vert, pszFragSource);
auto glprogramstate = GLProgramState::getOrCreateWithGLProgram(glprogram);
setGLProgramState(glprogramstate);
CHECK_GL_ERROR_DEBUG();
return true;
} while (0);
return false;
}
void FilterSprite::setFilterMat(cocos2d::Mat4 matrixArray)
{
m_uSpriteFilter=matrixArray;
}
void FilterSprite::draw(Renderer *renderer, const Mat4 &transform, uint32_t flags)
{
_customCommand.init(_globalZOrder);
_customCommand.func = CC_CALLBACK_0(FilterSprite::onDraw, this, transform, flags);
renderer->addCommand(&_customCommand);
}
void FilterSprite::onDraw(const Mat4 &transform, uint32_t flags)
{
auto glProgramState = getGLProgramState();
glProgramState->setUniformMat4(“fiterMat”,m_uSpriteFilter);
glProgramState->apply(transform);
GL::blendFunc( _blendFunc.src, _blendFunc.dst );
GL::bindTexture2D( _texture->getName() );
GL::enableVertexAttribs( GL::VERTEX_ATTRIB_FLAG_POS_COLOR_TEX );
#define kQuadSize sizeof(_quad.bl)
size_t offset = (size_t)&_quad;
// vertex
int diff = offsetof( V3F_C4B_T2F, vertices);
glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_POSITION, 3, GL_FLOAT, GL_FALSE, kQuadSize, (void*) (offset + diff));
// texCoods
diff = offsetof( V3F_C4B_T2F, texCoords);
glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_TEX_COORD, 2, GL_FLOAT, GL_FALSE, kQuadSize, (void*)(offset + diff));
// color
diff = offsetof( V3F_C4B_T2F, colors);
glVertexAttribPointer(GLProgram::VERTEX_ATTRIB_COLOR, 4, GL_UNSIGNED_BYTE, GL_TRUE, kQuadSize, (void*)(offset + diff));
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
CHECK_GL_ERROR_DEBUG();
CC_INCREMENT_GL_DRAWN_BATCHES_AND_VERTICES(1,4);
}