bool RenderTexture::initWithWidthAndHeight(int w, int h, Texture2D::PixelFormat format, GLuint depthStencilFormat){ CCASSERT(format != Texture2D::PixelFormat::A8, “only RGB and RGBA formats are valid for a render texture”); bool ret = false; void data = nullptr; do { _fullRect = _rtTextureRect = Rect(0,0,w,h); //Size size = Director::getInstance()->getWinSizeInPixels(); //_fullviewPort = Rect(0,0,size.width,size.height); w = (int)(w * CC_CONTENT_SCALE_FACTOR()); h = (int)(h * CC_CONTENT_SCALE_FACTOR()); _fullviewPort = Rect(0,0,w,h); glGetIntegerv(GL_FRAMEBUFFER_BINDING, &_oldFBO); // textures must be power of two squared int powW = 0; int powH = 0; if (Configuration::getInstance()->supportsNPOT()) { powW = w; powH = h; } else { powW = ccNextPOT(w); powH = ccNextPOT(h); } auto dataLen = powW * powH * 4;
//这里为什么要4 data = malloc(dataLen); CC_BREAK_IF(! data); memset(data, 0, dataLen); _pixelFormat = format; _texture = new Texture2D(); if (_texture) { _texture->initWithData(data, dataLen, (Texture2D::PixelFormat)_pixelFormat, powW, powH, Size((float)w, (float)h)); } else { break; } GLint oldRBO; glGetIntegerv(GL_RENDERBUFFER_BINDING, &oldRBO); if (Configuration::getInstance()->checkForGLExtension(“GL_QCOM”)) { _textureCopy = new Texture2D(); if (_textureCopy) { _textureCopy->initWithData(data, dataLen, (Texture2D::PixelFormat)_pixelFormat, powW, powH, Size((float)w, (float)h)); } else { break; } } // generate FBO glGenFramebuffers(1, &_FBO); glBindFramebuffer(GL_FRAMEBUFFER, _FBO); // associate texture with FBO glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, _texture->getName(), 0); if (depthStencilFormat != 0) { //create and attach depth buffer glGenRenderbuffers(1, &_depthRenderBufffer); glBindRenderbuffer(GL_RENDERBUFFER, _depthRenderBufffer); glRenderbufferStorage(GL_RENDERBUFFER, depthStencilFormat, (GLsizei)powW, (GLsizei)powH); glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, _depthRenderBufffer); // if depth format is the one with stencil part, bind same render buffer as stencil attachment if (depthStencilFormat == GL_DEPTH24_STENCIL8) { glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_STENCIL_ATTACHMENT, GL_RENDERBUFFER, _depthRenderBufffer); } } // check if it worked (probably worth doing 
) CCASSERT(glCheckFramebufferStatus(GL_FRAMEBUFFER) == GL_FRAMEBUFFER_COMPLETE, “Could not attach texture to framebuffer”); _texture->setAliasTexParameters(); // retained setSprite(Sprite::createWithTexture(_texture)); _texture->release(); _sprite->setFlippedY(true); _sprite->setBlendFunc( BlendFunc::ALPHA_PREMULTIPLIED ); glBindRenderbuffer(GL_RENDERBUFFER, oldRBO); glBindFramebuffer(GL_FRAMEBUFFER, _oldFBO); // Diabled by default. _autoDraw = false; // add sprite for backward compatibility addChild(_sprite); ret = true; } while (0); CC_SAFE_FREE(data); return ret;}
如上面代码中标明红色的地方，取到纹理宽高后为什么还要*4呢
powW * powH * 4
rgba四个字节