vkCmdDrawIndirectCount

vkCmdDrawIndirectCount is a Vulkan command that allows for indirect drawing calls. Unlike a standard vkCmdDraw command where the vertex count, instance count, and offsets are provided directly, vkCmdDrawIndirectCount retrieves these parameters from a buffer. This buffer, known as the indirect buffer, contains structured data that specifies how many vertices, instances, and the offsets to use for the draw call.

The primary advantage of vkCmdDrawIndirectCount is its ability to dynamically control drawing parameters on the GPU without requiring CPU intervention for every draw. This is particularly useful for scenarios such as instanced rendering where the number of instances might change frequently based on GPU-driven logic, or for culling operations that determine which objects to draw.

The indirect buffer can be populated by the CPU or, more powerfully, by other GPU commands. For example, a compute shader could perform culling or generate an indirect buffer containing the draw parameters for visible objects. This enables complex, GPU-driven rendering pipelines.

The command takes several arguments, including the command buffer to record the command into, a buffer containing the draw parameters, an offset into that buffer, the buffer containing the count of draw calls, an offset into the count buffer, and the stride between draw parameter structures. Using vkCmdDrawIndirectCount can significantly improve performance by reducing CPU overhead and enabling more efficient GPU utilization.