Multiple Vulkan buffer binding points

vk.cpp

Shader

layout (location = 0) in vec3 inPos;
layout (location = 1) in vec3 inColor;
layout (location = 2) in vec3 inPosB;
layout (location = 3) in vec3 inColorB;

...

Application

// Input state
std::array<VkVertexInputBindingDescription,2> vertexInputBinding = {};
vertexInputBinding[0].binding = 0;
vertexInputBinding[0].stride = sizeof(Vertex);
vertexInputBinding[0].inputRate = VK_VERTEX_INPUT_RATE_VERTEX;
vertexInputBinding[1].binding = 1;
vertexInputBinding[1].stride = sizeof(Vertex);
vertexInputBinding[1].inputRate = VK_VERTEX_INPUT_RATE_VERTEX;

// Inpute attribute bindings describe shader attribute locations and memory layouts
std::array<VkVertexInputAttributeDescription, 4> vertexInputAttributs;
vertexInputAttributs[0].binding = 0;
vertexInputAttributs[0].location = 0;
vertexInputAttributs[0].format = VK_FORMAT_R32G32B32_SFLOAT;
vertexInputAttributs[0].offset = offsetof(Vertex, position);
vertexInputAttributs[1].binding = 0;
vertexInputAttributs[1].location = 1;
vertexInputAttributs[1].format = VK_FORMAT_R32G32B32_SFLOAT;
vertexInputAttributs[1].offset = offsetof(Vertex, color);

vertexInputAttributs[2].binding = 1;
vertexInputAttributs[2].location = 2;
vertexInputAttributs[2].format = VK_FORMAT_R32G32B32_SFLOAT;
vertexInputAttributs[2].offset = offsetof(Vertex, position);
vertexInputAttributs[3].binding = 1;
vertexInputAttributs[3].location = 3;
vertexInputAttributs[3].format = VK_FORMAT_R32G32B32_SFLOAT;
vertexInputAttributs[3].offset = offsetof(Vertex, color);

// Vertex input state used for pipeline creation
VkPipelineVertexInputStateCreateInfo vertexInputState = {};
vertexInputState.sType = VK_STRUCTURE_TYPE_PIPELINE_VERTEX_INPUT_STATE_CREATE_INFO;
vertexInputState.vertexBindingDescriptionCount = 2;
vertexInputState.pVertexBindingDescriptions = vertexInputBinding.data();
vertexInputState.vertexAttributeDescriptionCount = 4;
vertexInputState.pVertexAttributeDescriptions = vertexInputAttributs.data();

// Bind
vkCmdBindVertexBuffers(drawCmdBuffers[i], 0, 1, &vertices.buffer, offsets);
vkCmdBindVertexBuffers(drawCmdBuffers[i], 1, 1, &verticesB.buffer, offsets);

why not put both of vertex datas into the same buffer?It seems that they will be handled within the same shader?

Because there are usages where you might want to modify one of the attributes but not the other? For example, texture map coordinates. You could have a texture 'slide' across an object.
For that, though the 3D coordinates and the normals of the vertices would not change, you would need to change the texture coordinates. Probably cheaper to have two separate buffers, one with coordinates and normals and the other with the texture coordinates. It's less work than re-building a full interleaved data and copying a larger buffer from your CPU to your GPU.

why not put both of vertex datas into the same buffer?It seems that they will be handled within the same shader?

I am under the impression that this is an example that teaches us how to properly use vertex input attributes and not an example that is meant to demonstrate optimal usage of buffers. I believe the you are right and using the same buffer would have been a great idea. :)