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Copy file name to clipboardExpand all lines: en/04_Vertex_buffers/00_Vertex_input_description.adoc
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@@ -58,7 +58,8 @@ Create a new structure called `Vertex` with the two attributes that we're going
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[,c++]
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----
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struct Vertex {
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struct Vertex
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{
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glm::vec2 pos;
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glm::vec3 color;
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};
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The next step is to tell Vulkan how to pass this data format to the vertex shader once it's been uploaded into GPU memory.
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There are two types of structures needed to convey this information.
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The first structure is `VkVertexInputBindingDescription` and we'll add a member function to the `Vertex` struct to populate it with the right data.
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The first structure is `vk::VertexInputBindingDescription` and we'll add a member function to the `Vertex` struct to populate it with the right data.
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[,c++]
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----
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The `binding` parameter specifies the index of the binding in the array of bindings.
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The `stride` parameter specifies the number of bytes from one entry to the next, and the `inputRate` parameter can have one of the following values:
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* `VK_VERTEX_INPUT_RATE_VERTEX`: Move to the next data entry after each vertex
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* `VK_VERTEX_INPUT_RATE_INSTANCE`: Move to the next data entry after each instance
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* `vk::VertexInputRate::eVertex` : Move to the next data entry after each vertex
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* `vk::VertexInputRate::eInstance`: Move to the next data entry after each instance
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We're not going to use instanced rendering, so we'll stick to per-vertex data.
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== Attribute descriptions
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The second structure that describes how to handle vertex input is `VkVertexInputAttributeDescription`.
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The second structure that describes how to handle vertex input is `vk::VertexInputAttributeDescription`.
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We're going to add another helper function to `Vertex` to fill in these structs.
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A bit confusingly, the formats are specified using the same enumeration as color formats.
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The following shader types and formats are commonly used together:
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* `float`: `VK_FORMAT_R32_SFLOAT`
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* `float2`: `VK_FORMAT_R32G32_SFLOAT`
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* `float3`: `VK_FORMAT_R32G32B32_SFLOAT`
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* `float4`: `VK_FORMAT_R32G32B32A32_SFLOAT`
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* `float`: `vk::Format::eR32Sfloat`
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* `float2`: `vk::Format::eR32G32Sfloat`
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* `float3`: `vk::Format::eR32G32B32Sfloat`
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* `float4`: `vk::Format::eR32G32B32A32Sfloat`
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As you can see, you should use the format where the amount of color channels matches the number of components in the shader data type.
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It is allowed to use more channels than the number of components in the shader, but they will be silently discarded.
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If the number of channels is lower than the number of components, then the BGA components will use default values of `(0, 0, 1)`.
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The color type (`SFLOAT`, `UINT`, `SINT`) and bit width should also match the type of the shader input.
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The color type (`Sfloat`, `Uint`, `Sint`) and bit width should also match the type of the shader input.
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See the following examples:
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* `int2`: `VK_FORMAT_R32G32_SINT`, a 2-component vector of 32-bit signed
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integers
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* `uint4`: `VK_FORMAT_R32G32B32A32_UINT`, a 4-component vector of 32-bit
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unsigned integers
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* `double`: `VK_FORMAT_R64_SFLOAT`, a double-precision (64-bit) float
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* `int2` : `vk::Format::eR32G32Sint`, a 2-component vector of 32-bit signed integers
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* `uint4` : `vk::Format::eR32G32B32A32Uint`, a 4-component vector of 32-bit unsigned integers
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* `double`: `vk::Format::eR64Sfloat`, a double-precision (64-bit) float
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The `format` parameter implicitly defines the byte size of attribute data and the `offset` parameter has specified the number of bytes since the start of the per-vertex data to read from.
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The binding is loading one `Vertex` at a time and the position attribute (`pos`) is at an offset of `0` bytes from the beginning of this struct.
@@ -171,17 +170,18 @@ Find the `vertexInputInfo` struct and modify it to reference the two description
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----
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auto bindingDescription = Vertex::getBindingDescription();
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auto attributeDescriptions = Vertex::getAttributeDescriptions();
In the xref:./02_Staging_buffer.adoc[next chapter,] we'll look at a different way to copy vertex data to a vertex buffer that results in better performance, but takes some more work.
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