Vertex Buffer

Data conversion

Blender can use a GPU_COMP_I32/GPU_COMP_U32 and use GPU_FETCH_INT_TO_FLOAT to bind it to a float attribute. Vulkan doesn't support this because it adds no benefit to the GPU.

Note

GPU_COMP_U8/I8/U16/I16 with GPU_FETCH_INT_TO_FLOAT are natively supported as they trade in a bit of work to reduce memory bandwidth.

Although we should remove these cases in the code-base, we should still add the data conversion as add-ons might use them.

vk_data_conversion.hh

bool conversion_needed(const GPUVertFormat &vertex_format);
void convert_in_place(void *data, const GPUVertFormat &vertex_format, const uint vertex_len);

Based on a GPUVertFormat it can be checked if there are some attributes that requires conversion on the host side.

convert_in_place only changes the buffer (data) the vertex_format is still the original.

When binding the vertex buffers to the shader the VkFormat of those attributes are also changed.

vk_common.hh

VkFormat to_vk_format(const GPUVertCompType type,
                      const uint32_t size,
                      const GPUVertFetchMode fetch_mode);

GPU_COMP_I32/GPU_COMP_U32 with GPU_FETCH_INT_TO_FLOAT would return a VK_FORMAT_*_SFLOAT as the data should already be converted to floats by calling convert_in_place.

GPUVertCompType	GPUVertFetchMode	VkFormat
GPU_COMP_I8	GPU_FETCH_INT_TO_FLOAT	VK_FORMAT_R8_SSCALED
GPU_COMP_U8	GPU_FETCH_INT_TO_FLOAT	VK_FORMAT_R8_USCALED
GPU_COMP_I16	GPU_FETCH_INT_TO_FLOAT	VK_FORMAT_R16_SSCALED
GPU_COMP_U16	GPU_FETCH_INT_TO_FLOAT	VK_FORMAT_R16_USCALED
GPU_COMP_I32	GPU_FETCH_INT_TO_FLOAT	VK_FORMAT_R32_SFLOAT
GPU_COMP_U32	GPU_FETCH_INT_TO_FLOAT	VK_FORMAT_R32_SFLOAT
GPU_COMP_F32	GPU_FETCH_FLOAT	VK_FORMAT_R32_SFLOAT