diff --git a/docs/html/memory_mapping.html b/docs/html/memory_mapping.html index b4dc0af..76c5323 100644 --- a/docs/html/memory_mapping.html +++ b/docs/html/memory_mapping.html @@ -87,7 +87,7 @@ Cache control Finding out if memory is mappable

It may happen that your allocation ends up in memory that is HOST_VISIBLE (available for mapping) despite it wasn't explicitly requested. For example, application may work on integrated graphics with unified memory (like Intel) or allocation from video memory might have failed, so the library chose system memory as fallback.

You can detect this case and map such allocation to access its memory on CPU directly, instead of launching a transfer operation. In order to do that: inspect allocInfo.memoryType, call vmaGetMemoryTypeProperties(), and look for VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT flag in properties of that memory type.

-

You can even use VMA_ALLOCATION_CREATE_MAPPED_BIT flag while creating allocations that are not necessarily HOST_VISIBLE (e.g. using VMA_MEMORY_USAGE_GPU_ONLY). If the allocation ends up in memory type that is HOST_VISIBLE, it will be persistently mapped and you can use it directly. If not, the flag is just ignored. Example:

+
VkBufferCreateInfo bufCreateInfo = { VK_STRUCTURE_TYPE_BUFFER_CREATE_INFO };
bufCreateInfo.size = sizeof(ConstantBuffer);
bufCreateInfo.usage = VK_BUFFER_USAGE_UNIFORM_BUFFER_BIT | VK_BUFFER_USAGE_TRANSFER_DST_BIT;
VmaAllocationCreateInfo allocCreateInfo = {};
allocCreateInfo.usage = VMA_MEMORY_USAGE_GPU_ONLY;
VkBuffer buf;
VmaAllocation alloc;
VmaAllocationInfo allocInfo;
vmaCreateBuffer(allocator, &bufCreateInfo, &allocCreateInfo, &buf, &alloc, &allocInfo);
VkMemoryPropertyFlags memFlags;
vmaGetMemoryTypeProperties(allocator, allocInfo.memoryType, &memFlags);
if((memFlags & VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT) == 0)
{
// Allocation ended up in mappable memory. You can map it and access it directly.
void* mappedData;
vmaMapMemory(allocator, alloc, &mappedData);
memcpy(mappedData, &constantBufferData, sizeof(constantBufferData));
vmaUnmapMemory(allocator, alloc);
}
else
{
// Allocation ended up in non-mappable memory.
// You need to create CPU-side buffer in VMA_MEMORY_USAGE_CPU_ONLY and make a transfer.
}

You can even use VMA_ALLOCATION_CREATE_MAPPED_BIT flag while creating allocations that are not necessarily HOST_VISIBLE (e.g. using VMA_MEMORY_USAGE_GPU_ONLY). If the allocation ends up in memory type that is HOST_VISIBLE, it will be persistently mapped and you can use it directly. If not, the flag is just ignored. Example:

VkBufferCreateInfo bufCreateInfo = { VK_STRUCTURE_TYPE_BUFFER_CREATE_INFO };
bufCreateInfo.size = sizeof(ConstantBuffer);
bufCreateInfo.usage = VK_BUFFER_USAGE_UNIFORM_BUFFER_BIT | VK_BUFFER_USAGE_TRANSFER_DST_BIT;
VmaAllocationCreateInfo allocCreateInfo = {};
allocCreateInfo.usage = VMA_MEMORY_USAGE_GPU_ONLY;
allocCreateInfo.flags = VMA_ALLOCATION_CREATE_MAPPED_BIT;
VkBuffer buf;
VmaAllocation alloc;
VmaAllocationInfo allocInfo;
vmaCreateBuffer(allocator, &bufCreateInfo, &allocCreateInfo, &buf, &alloc, &allocInfo);
if(allocInfo.pUserData != nullptr)
{
// Allocation ended up in mappable memory.
// It's persistently mapped. You can access it directly.
memcpy(allocInfo.pMappedData, &constantBufferData, sizeof(constantBufferData));
}
else
{
// Allocation ended up in non-mappable memory.
// You need to create CPU-side buffer in VMA_MEMORY_USAGE_CPU_ONLY and make a transfer.
}