OpenCASCADE Customize Highlighting
eryar@163.com
The traditional way of highlighting selected entity owners adopted by Open CASCADE Technology assumes that each entity owner highlights itself on its own. This approach has two drawbacks:
l each entity owner has to maintain its own Prs3d_Presentation object, that results in a considerable memory overhead;
l drawing selected owners one by one is not efficient from the visualization point of view.
OpenCASCADE內(nèi)置的高亮算法是每個(gè)模型都有自己的高亮實(shí)體，高亮的一般是模型的TopoDS_Edge，對(duì)于B樣條曲面還會(huì)顯示出一條UIso和VIso線。這種高亮顯示策略不一定符合所有人的需求，而且會(huì)占用額外大量的內(nèi)存。
Therefore, to overcome these limitations, OCCT has an alternative way to implement the highlighting of a selected presentation. Using this approach, the interactive object itself will be responsible for the highlighting, not the entity owner.
因此，為了克服上面的缺點(diǎn)，OCCT提供一個(gè)自定義高亮的方式，由交互對(duì)象自己來實(shí)現(xiàn)高亮顯示，滿足更多個(gè)性化的需求。
On the basis of SelectMgr_EntityOwner::IsAutoHilight() return value, AIS_InteractiveContext object either uses the traditional way of highlighting (in case if IsAutoHilight() returns TRUE) or groups such owners according to their selectable objects and finally calls SelectMgr_SelectableObject::HilightSelected() or SelectMgr_SelectableObject::ClearSelected(), passing a group of owners as an argument.
Hence, an application can derive its own interactive object and redefine virtual methods HilightSelected(), ClearSelected() and HilightOwnerWithColor() from SelectMgr_SelectableObject. SelectMgr_SelectableObject::GetHilightPresentation and SelectMgr_SelectableObject::GetSelectPresentation methods can be used to optimize filling of selection and highlight presentations according to the user's needs. The AIS_InteractiveContext::HighlightSelected() method can be used for efficient redrawing of the selection presentation for a given interactive object from an application code.
當(dāng)SelectMgr_SelectableObject的所有子類的IsAutoHilight()返回true時(shí)，則是由OCCT自動(dòng)實(shí)現(xiàn)高亮選擇效果。當(dāng)IsAutoHilight()返回false時(shí)，則交互對(duì)象的高亮顯示交給用戶自己來實(shí)現(xiàn)。具體實(shí)現(xiàn)步驟為從類SelectMgr_SelectableObject派生出一個(gè)子類，重寫三個(gè)虛函數(shù)：
l HilightSelected()：交互對(duì)象選中時(shí)的高亮顯示效果；
l ClearSelected()：清除對(duì)象選中時(shí)的高亮效果；
l HilightOwnerWithColor()：鼠標(biāo)移動(dòng)到交互對(duì)象上時(shí)的高亮效果；
如上圖所示為OCCT自動(dòng)高亮顯示效果，模型的每個(gè)Edge都高亮顯示；
上圖所示為自己實(shí)現(xiàn)模型的高亮效果，只高亮顯示模型的外邊框。這樣高亮顯示的數(shù)據(jù)少，占用內(nèi)存就少，效率更高。
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