OGRE渲染物体,可以把物体作为InstancedGeometry,StaticGeometry,Entity实例来渲染。
区别:
InstancedGeometry:Pre-transforms and batches up meshes for efficient use as instanced geometry in a scene。也就是说,把所有网格作为一个instance geometry。
this shader instancing implementation stores only 80 times the object, and then re-uses the vertex data with different shader parameter.只可以存储同一物体80次,然后重用顶点数据使用不同的渲染参数。
可以每帧调整位置,方向,大小等
StaticGeometry:把所有网格作为一个静态几何体,这样每个材质就是一次批次。但是,看到一小部分,整个StaticGeometry也会全部都渲染的。
Entity:每个Entity包含一个Mesh。
每次渲染操作都是相当的耗费资源的。所以应该减少对DIP的调用。
OGRE的渲染流程
void SceneManager::renderSingleObject(Renderable* rend, const Pass* pass, ...)
{
//...
static RenderOperation ro;
ro.srcRenderable = rend;
//...
mDestRenderSystem->_render(ro);
//...
}
void SceneManager::SceneMgrQueuedRenderableVisitor::visit(Renderable* r)
{
// Give SM a chance to eliminate
if (targetSceneMgr->validateRenderableForRendering(mUsedPass, r))
{
// Render a single object, this will set up auto params if required
targetSceneMgr->renderSingleObject(r, mUsedPass, scissoring, autoLights, manualLightList);
}
}
void QueuedRenderableCollection::acceptVisitorGrouped(
QueuedRenderableVisitor* visitor) const
{
PassGroupRenderableMap::const_iterator ipass, ipassend;
ipassend = mGrouped.end();
for (ipass = mGrouped.begin(); ipass != ipassend; ++ipass)
{
// Fast bypass if this group is now empty
if (ipass->second->empty()) continue;
// Visit Pass - allow skip
if (!visitor->visit(ipass->first))
continue;
RenderableList* rendList = ipass->second;
RenderableList::const_iterator irend, irendend;
irendend = rendList->end();
for (irend = rendList->begin(); irend != irendend; ++irend)
{
// Visit Renderable
visitor->visit(const_cast<Renderable*>(*irend));
}
}
}
for (ipass = mGrouped.begin(); ipass != ipassend; ++ipass)
{
________//....
________RenderableList* rendList = ipass->second;
________for (irend = rendList->begin(); irend != irendend; ++irend)
______________ {
_________________visitor->visit(const_cast<Renderable*>(*irend));
______________ }
}
也就是说每个Rendable都会调用一次DIP。当把有相同的Pass的Rendable合并成一次时,可以减少对DIP的调用。