Fix buffer usages, stylistic choice and magic number usages.

Author: kevyuu

include/nbl/asset/utils/CPolygonGeometryManipulator.h

@@ -87,16 +87,23 @@ class NBL_API2 CPolygonGeometryManipulator
 			if (!indexing) return nullptr;
 			if (indexing->degree() != 3) return nullptr;
 
+			const auto originalView = geo->getIndexView();
 			const auto primCount = geo->getPrimitiveCount();
 			const auto maxIndex = geo->getPositionView().getElementCount() - 1;
 			const uint8_t indexSize = maxIndex <= std::numeric_limits<uint16_t>::max() ? sizeof(uint16_t) : sizeof(uint32_t);
-      const auto outGeometry = core::move_and_static_cast<ICPUPolygonGeometry>(geo->clone(0u));
+			const auto outGeometry = core::move_and_static_cast<ICPUPolygonGeometry>(geo->clone(0u));
 
 			if (indexing && indexing->knownTopology() == EPT_TRIANGLE_LIST) 
 				return outGeometry;
 
+			
 			auto* outGeo = outGeometry.get();
-			auto indexBuffer = ICPUBuffer::create({ primCount * 3 * indexSize, IBuffer::EUF_INDEX_BUFFER_BIT });
+			const auto indexBufferUsages = [&]
+			{
+					if (originalView) return originalView.src.buffer->getUsageFlags();
+					return IBuffer::EUF_INDEX_BUFFER_BIT;
+			}();
+			auto indexBuffer = ICPUBuffer::create({ primCount * indexing->degree() * indexSize, indexBufferUsages });
 			auto indexBufferPtr = indexBuffer->getPointer();
 			auto indexView = ICPUPolygonGeometry::SDataView{
 				.composed = {
@@ -109,42 +116,49 @@ class NBL_API2 CPolygonGeometryManipulator
 				}
 			};
 
-			if (indexSize == 2)
+			switch (indexSize)
 			{
-				IPolygonGeometryBase::IIndexingCallback::SContext<uint16_t> context{
-					.indexBuffer = outGeo->getIndexView().getPointer(),
-					.indexSize = indexSize,
-					.beginPrimitive = 0,
-					.endPrimitive = primCount,
-					.out = indexBufferPtr,
-				};
-				indexing->operator()(context);
-
-				indexView.composed.encodedDataRange.u16.minVx[0] = 0;
-				indexView.composed.encodedDataRange.u16.maxVx[0] = maxIndex;
-				indexView.composed.format = EF_R16_UINT;
-				indexView.composed.rangeFormat = IGeometryBase::EAABBFormat::U16;
-
-			} else
-			{
-				IPolygonGeometryBase::IIndexingCallback::SContext<uint32_t> context{
-					.indexBuffer = outGeo->getIndexView().getPointer(),
-					.indexSize = indexSize,
-					.beginPrimitive = 0,
-					.endPrimitive = primCount,
-					.out = indexBufferPtr,
-				};
-				indexing->operator()(context);
-
-				indexView.composed.encodedDataRange.u32.minVx[0] = 0;
-				indexView.composed.encodedDataRange.u32.maxVx[0] = maxIndex;
-				indexView.composed.format = EF_R32_UINT;
-				indexView.composed.rangeFormat = IGeometryBase::EAABBFormat::U32;
+				case 2:
+				{
+					IPolygonGeometryBase::IIndexingCallback::SContext<uint16_t> context{
+						.indexBuffer = geo->getIndexView().getPointer(),
+						.indexSize = indexSize,
+						.beginPrimitive = 0,
+						.endPrimitive = primCount,
+						.out = indexBufferPtr,
+					};
+					indexing->operator()(context);
+
+					indexView.composed.encodedDataRange.u16.minVx[0] = 0;
+					indexView.composed.encodedDataRange.u16.maxVx[0] = maxIndex;
+					indexView.composed.format = EF_R16_UINT;
+					indexView.composed.rangeFormat = IGeometryBase::EAABBFormat::U16;
+					break;
+				}
+				case 4:
+				{
+					IPolygonGeometryBase::IIndexingCallback::SContext<uint32_t> context{
+						.indexBuffer = geo->getIndexView().getPointer(),
+						.indexSize = indexSize,
+						.beginPrimitive = 0,
+						.endPrimitive = primCount,
+						.out = indexBufferPtr,
+					};
+					indexing->operator()(context);
+
+					indexView.composed.encodedDataRange.u32.minVx[0] = 0;
+					indexView.composed.encodedDataRange.u32.maxVx[0] = maxIndex;
+					indexView.composed.format = EF_R32_UINT;
+					indexView.composed.rangeFormat = IGeometryBase::EAABBFormat::U32;
+					break;
+				}
+				default:
+					assert(false);
 			}
 
 			outGeo->setIndexing(IPolygonGeometryBase::TriangleList());
 			outGeo->setIndexView(std::move(indexView));
-			recomputeContentHashes(outGeo);
+			CGeometryManipulator::recomputeContentHash(outGeo->getIndexView());
 
 			return outGeometry;
 		}