If we had a descriptor set that had binding 0, 2 and 3 using static uniform buffer, and bindings 1,4,5 using dynamic descriptors, we would need to send 3 uint32_t to the bind function.ĭynamic uniform buffer bindings can be slightly slower in the GPU than hardcoded ones, but in general is such a low difference that it’s hard to measure. Because the binding number 0 has no dynamic offset, sending 1 offset to the function will affect the second binding, where we do have the dynamic descriptor. We need to send the offset to the vkCmdBindDescriptorSets() call. binding for camera data at 0 VkDescriptorSetLayoutBinding cameraBind = vkinit :: descriptorset_layout_binding ( VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER, VK_SHADER_STAGE_VERTEX_BIT, 0 ) //binding for scene data at 1 VkDescriptorSetLayoutBinding sceneBind = vkinit :: descriptorset_layout_binding ( VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER, VK_SHADER_STAGE_VERTEX_BIT | VK_SHADER_STAGE_FRAGMENT_BIT, 1 ) VkDescriptorSetLayoutBinding bindings = The struct will contain most GPU properties, so it’s useful to keep it around. We are going to add a VkPhysicalDeviceProperties member to the VulkanEngine class, and make Vulkan fill it. To do that, we are going to add some code to init_vulkan() where we are going to request GPU information and store the minimum alignment that we need. We can see that all GPUs at least support an alignment of 256 bytes, but we are going to check it at runtime anyway. You can look at said limit in the vulkaninfo page Link The limit we are looking for is called minUniformBufferOffsetAlignment.
To know what is the minimum alignment size for buffers, we need to query it from the GPU. The GPUs often can’t read from an arbitrary address, and your buffer offsets have to be aligned into a certain minimum size. The main complication that comes from sub allocating data on a buffer, is that you need to be very mindful of alignment. There are some very nice techniques that can be done with that, like dynamic descriptors, that allow to reuse the same descriptor set over and over again but every time with a different offset into the buffer. But instead of holding it as 2 buffers, we will store it on one buffer.Īllocating multiple things into the same buffer is generally a good idea in Vulkan. We will add a “environment data” buffer, holding information like ambient tint and fog settings. We can have multiple descriptors point into different parts of the same buffer.
But we don’t need to have 1 descriptor point to 1 buffer. Each of them points into a different VkBuffer, and we hold the camera information there.
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