X Window研究笔记(11)
时间：2010-03-31 来源：erlongabc
转载时请注明出处和作者联系方式
作者联系方式：李先静 <xianjimli at hotmail dot com>
11.X Window扩展机制－－对象装饰
Decorator模式是一个非常重要的模式，它在不影响其他对象的情况下，以动态、透 明的方式给单个对象添加职责。X Server是用C开发的，不方便使用正统的装饰模式，但大量使用了类似装饰模式的扩展方式。可以被装饰的对象有：
其实现过程可以这样理解：
其中，用得最多的是对 ScreenRec的装饰，下面我们以sprite模块中对ScreenRec的装饰为例，分析一下它的实现原理：
sprite指像鼠标 指针一类的屏幕精灵，它的特点是，形状可能不规则，可以在屏幕上移动，会覆盖当前位置的图像，当它移动到新的位置时，自动恢复先前位置的图像。
sprite 的初始化是在miSpriteInitialize中完成的：
Bool
miSpriteInitialize (pScreen, cursorFuncs, screenFuncs)
ScreenPtr pScreen;
miSpriteCursorFuncPtr cursorFuncs;
miPointerScreenFuncPtr screenFuncs;
...{
miSpriteScreenPtr pPriv;
VisualPtr pVisual;
#ifdef RENDER
PictureScreenPtr ps = GetPictureScreenIfSet(pScreen);
#endif
if (miSpriteGeneration != serverGeneration)
...{
miSpriteScreenIndex = AllocateScreenPrivateIndex ();
if (miSpriteScreenIndex < 0)
return FALSE;
miSpriteGeneration = serverGeneration;
miSpriteGCIndex = AllocateGCPrivateIndex ();
}
if (!AllocateGCPrivate(pScreen, miSpriteGCIndex, sizeof(miSpriteGCRec)))
return FALSE;
pPriv = (miSpriteScreenPtr) xalloc (sizeof (miSpriteScreenRec));
if (!pPriv)
return FALSE;
if (!miPointerInitialize (pScreen, &miSpritePointerFuncs, screenFuncs,TRUE))
...{
xfree ((pointer) pPriv);
return FALSE;
}
for (pVisual = pScreen->visuals;
pVisual->vid != pScreen->rootVisual;
pVisual++)
;
pPriv->pVisual = pVisual;
pPriv->CloseScreen = pScreen->CloseScreen;
pPriv->GetImage = pScreen->GetImage;
pPriv->GetSpans = pScreen->GetSpans;
pPriv->SourceValidate = pScreen->SourceValidate;
pPriv->CreateGC = pScreen->CreateGC;
pPriv->BlockHandler = pScreen->BlockHandler;
pPriv->InstallColormap = pScreen->InstallColormap;
pPriv->StoreColors = pScreen->StoreColors;
pPriv->PaintWindowBackground = pScreen->PaintWindowBackground;
pPriv->PaintWindowBorder = pScreen->PaintWindowBorder;
pPriv->CopyWindow = pScreen->CopyWindow;
pPriv->ClearToBackground = pScreen->ClearToBackground;
pPriv->SaveDoomedAreas = pScreen->SaveDoomedAreas;
pPriv->RestoreAreas = pScreen->RestoreAreas;
#ifdef RENDER
if (ps)
...{
pPriv->Composite = ps->Composite;
pPriv->Glyphs = ps->Glyphs;
}
#endif
pPriv->pCursor = NULL;
pPriv->x = 0;
pPriv->y = 0;
pPriv->isUp = FALSE;
pPriv->shouldBeUp = FALSE;
pPriv->pCacheWin = NullWindow;
pPriv->isInCacheWin = FALSE;
pPriv->checkPixels = TRUE;
pPriv->pInstalledMap = NULL;
pPriv->pColormap = NULL;
pPriv->funcs = cursorFuncs;
pPriv->colors[SOURCE_COLOR].red = 0;
pPriv->colors[SOURCE_COLOR].green = 0;
pPriv->colors[SOURCE_COLOR].blue = 0;
pPriv->colors[MASK_COLOR].red = 0;
pPriv->colors[MASK_COLOR].green = 0;
pPriv->colors[MASK_COLOR].blue = 0;
pScreen->devPrivates[miSpriteScreenIndex].ptr = (pointer) pPriv;
pScreen->CloseScreen = miSpriteCloseScreen;
pScreen->GetImage = miSpriteGetImage;
pScreen->GetSpans = miSpriteGetSpans;
pScreen->SourceValidate = miSpriteSourceValidate;
pScreen->CreateGC = miSpriteCreateGC;
pScreen->BlockHandler = miSpriteBlockHandler;
pScreen->InstallColormap = miSpriteInstallColormap;
pScreen->StoreColors = miSpriteStoreColors;
pScreen->PaintWindowBackground = miSpritePaintWindowBackground;
pScreen->PaintWindowBorder = miSpritePaintWindowBorder;
pScreen->CopyWindow = miSpriteCopyWindow;
pScreen->ClearToBackground = miSpriteClearToBackground;
pScreen->SaveDoomedAreas = miSpriteSaveDoomedAreas;
pScreen->RestoreAreas = miSpriteRestoreAreas;
#ifdef RENDER
if (ps)
...{
ps->Composite = miSpriteComposite;
ps->Glyphs = miSpriteGlyphs;
}
#endif
return TRUE;
}
这个函数有点长，但我 们只需要理解关键几点：
这里要特别说明的是，所谓的原始函数指针，并非一定是原装正品，可能已经是被别的模块装饰之后的函数。
下面 我们继续看函数调用的实现：
static void
miSpritePaintWindowBackground (pWin, pRegion, what)
WindowPtr pWin;
RegionPtr pRegion;
int what;
...{
ScreenPtr pScreen;
miSpriteScreenPtr pScreenPriv;
pScreen = pWin->drawable.pScreen;
SCREEN_PROLOGUE (pScreen, PaintWindowBackground);
pScreenPriv = (miSpriteScreenPtr) pScreen->devPrivates[miSpriteScreenIndex].ptr;
if (pScreenPriv->isUp)
...{
/**//*
* If the cursor is on the same screen as the window, check the
* region to paint for the cursor and remove it as necessary
*/
if (RECT_IN_REGION( pScreen, pRegion, &pScreenPriv->saved) != rgnOUT)
miSpriteRemoveCursor (pScreen);
}
(*pScreen->PaintWindowBackground) (pWin, pRegion, what);
SCREEN_EPILOGUE (pScreen, PaintWindowBackground, miSpritePaintWindowBackground);
}
为了看明白这段程序， 先得弄清楚两个宏：
SCREEN_PROLOGUE： 用于取出原始的函数指针，后面可以调用原始函数。
#define SCREEN_PROLOGUE(pScreen, field)\
((pScreen)->field = \
((miSpriteScreenPtr) (pScreen)->devPrivates[miSpriteScreenIndex].ptr)->field)
SCREEN_EPILOGUE： 重新把装饰过的放回去，以便于下次再调。
#define SCREEN_EPILOGUE(pScreen, field, wrapper)\
((pScreen)->field = wrapper)
弄清楚了这两个宏，上面的程序不难理解了。这种扩展方式的好处在于， 运行时动态为对象添加功能，同时又避免了扩展功能与框架的耦合，这是通过子类继承父类，然后重载部分虚函数无法实现的。
（待续）
作者联系方式：李先静 <xianjimli at hotmail dot com>
11.X Window扩展机制－－对象装饰
Decorator模式是一个非常重要的模式，它在不影响其他对象的情况下，以动态、透 明的方式给单个对象添加职责。X Server是用C开发的，不方便使用正统的装饰模式，但大量使用了类似装饰模式的扩展方式。可以被装饰的对象有：
- 屏幕: ScreenRec
- 窗口：WindowRec
- 图片: PixmapRec
- 绘图上下文: GC
- 颜色映射: Colormap
- 客户端：ClientRec
其实现过程可以这样理解：
- 初始化时，把原始对象的部 分函数指针保存下来，并用自己的函数去替代它。
- 调用时，装饰之后的函数被调用，在该函数 中，完成一些装饰性功能，并适当的位置调用原始的函数。
其中，用得最多的是对 ScreenRec的装饰，下面我们以sprite模块中对ScreenRec的装饰为例，分析一下它的实现原理：
sprite指像鼠标 指针一类的屏幕精灵，它的特点是，形状可能不规则，可以在屏幕上移动，会覆盖当前位置的图像，当它移动到新的位置时，自动恢复先前位置的图像。
sprite 的初始化是在miSpriteInitialize中完成的：
BoolmiSpriteInitialize (pScreen, cursorFuncs, screenFuncs) ScreenPtr pScreen; miSpriteCursorFuncPtr cursorFuncs; miPointerScreenFuncPtr screenFuncs;...{
...{ miSpriteScreenPtr pPriv; VisualPtr pVisual;#ifdef RENDER PictureScreenPtr ps = GetPictureScreenIfSet(pScreen);#endif if (miSpriteGeneration != serverGeneration) ...{
...{ miSpriteScreenIndex = AllocateScreenPrivateIndex (); if (miSpriteScreenIndex < 0) return FALSE; miSpriteGeneration = serverGeneration; miSpriteGCIndex = AllocateGCPrivateIndex (); } if (!AllocateGCPrivate(pScreen, miSpriteGCIndex, sizeof(miSpriteGCRec))) return FALSE; pPriv = (miSpriteScreenPtr) xalloc (sizeof (miSpriteScreenRec)); if (!pPriv) return FALSE; if (!miPointerInitialize (pScreen, &miSpritePointerFuncs, screenFuncs,TRUE)) ...{ xfree ((pointer) pPriv); return FALSE;}for (pVisual = pScreen->visuals; pVisual->vid != pScreen->rootVisual; pVisual++) ; pPriv->pVisual = pVisual; pPriv->CloseScreen = pScreen->CloseScreen; pPriv->GetImage = pScreen->GetImage; pPriv->GetSpans = pScreen->GetSpans; pPriv->SourceValidate = pScreen->SourceValidate; pPriv->CreateGC = pScreen->CreateGC; pPriv->BlockHandler = pScreen->BlockHandler; pPriv->InstallColormap = pScreen->InstallColormap; pPriv->StoreColors = pScreen->StoreColors; pPriv->PaintWindowBackground = pScreen->PaintWindowBackground; pPriv->PaintWindowBorder = pScreen->PaintWindowBorder; pPriv->CopyWindow = pScreen->CopyWindow; pPriv->ClearToBackground = pScreen->ClearToBackground; pPriv->SaveDoomedAreas = pScreen->SaveDoomedAreas; pPriv->RestoreAreas = pScreen->RestoreAreas;#ifdef RENDER if (ps) ...{ pPriv->Composite = ps->Composite; pPriv->Glyphs = ps->Glyphs; }#endif pPriv->pCursor = NULL; pPriv->x = 0; pPriv->y = 0; pPriv->isUp = FALSE; pPriv->shouldBeUp = FALSE; pPriv->pCacheWin = NullWindow; pPriv->isInCacheWin = FALSE; pPriv->checkPixels = TRUE;pPriv->pInstalledMap = NULL; pPriv->pColormap = NULL; pPriv->funcs = cursorFuncs; pPriv->colors[SOURCE_COLOR].red = 0; pPriv->colors[SOURCE_COLOR].green = 0; pPriv->colors[SOURCE_COLOR].blue = 0; pPriv->colors[MASK_COLOR].red = 0; pPriv->colors[MASK_COLOR].green = 0; pPriv->colors[MASK_COLOR].blue = 0; pScreen->devPrivates[miSpriteScreenIndex].ptr = (pointer) pPriv; pScreen->CloseScreen = miSpriteCloseScreen; pScreen->GetImage = miSpriteGetImage; pScreen->GetSpans = miSpriteGetSpans; pScreen->SourceValidate = miSpriteSourceValidate; pScreen->CreateGC = miSpriteCreateGC; pScreen->BlockHandler = miSpriteBlockHandler; pScreen->InstallColormap = miSpriteInstallColormap; pScreen->StoreColors = miSpriteStoreColors; pScreen->PaintWindowBackground = miSpritePaintWindowBackground; pScreen->PaintWindowBorder = miSpritePaintWindowBorder; pScreen->CopyWindow = miSpriteCopyWindow; pScreen->ClearToBackground = miSpriteClearToBackground; pScreen->SaveDoomedAreas = miSpriteSaveDoomedAreas; pScreen->RestoreAreas = miSpriteRestoreAreas;#ifdef RENDER if (ps) ...{ ps->Composite = miSpriteComposite; ps->Glyphs = miSpriteGlyphs; }#endif return TRUE;}
这个函数有点长，但我 们只需要理解关键几点：
- AllocateScreenPrivateIndex分 配私有数据空间，用于保存原始函数指针等信息。
- pPriv->PaintWindowBackground = pScreen->PaintWindowBackground; 之类的语句用于保存原始的函数指针。
- pScreen->PaintWindowBackground = miSpritePaintWindowBackground; 之类的语句用于把原始的函数指针替换为装饰之后的函数。
这里要特别说明的是，所谓的原始函数指针，并非一定是原装正品，可能已经是被别的模块装饰之后的函数。
下面 我们继续看函数调用的实现：
static voidmiSpritePaintWindowBackground (pWin, pRegion, what) WindowPtr pWin; RegionPtr pRegion; int what;...{ ScreenPtr pScreen; miSpriteScreenPtr pScreenPriv; pScreen = pWin->drawable.pScreen; SCREEN_PROLOGUE (pScreen, PaintWindowBackground); pScreenPriv = (miSpriteScreenPtr) pScreen->devPrivates[miSpriteScreenIndex].ptr; if (pScreenPriv->isUp) ...{ /**//* * If the cursor is on the same screen as the window, check the * region to paint for the cursor and remove it as necessary */ if (RECT_IN_REGION( pScreen, pRegion, &pScreenPriv->saved) != rgnOUT) miSpriteRemoveCursor (pScreen); } (*pScreen->PaintWindowBackground) (pWin, pRegion, what); SCREEN_EPILOGUE (pScreen, PaintWindowBackground, miSpritePaintWindowBackground);}
为了看明白这段程序， 先得弄清楚两个宏：
SCREEN_PROLOGUE： 用于取出原始的函数指针，后面可以调用原始函数。
#define SCREEN_PROLOGUE(pScreen, field)\
((pScreen)->field = \
((miSpriteScreenPtr) (pScreen)->devPrivates[miSpriteScreenIndex].ptr)->field)
SCREEN_EPILOGUE： 重新把装饰过的放回去，以便于下次再调。
#define SCREEN_EPILOGUE(pScreen, field, wrapper)\
((pScreen)->field = wrapper)
弄清楚了这两个宏，上面的程序不难理解了。这种扩展方式的好处在于， 运行时动态为对象添加功能，同时又避免了扩展功能与框架的耦合，这是通过子类继承父类，然后重载部分虚函数无法实现的。
（待续）
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