# ACMR

I think that the Average Cache Miss Ratio (ACMR) is not the best way of measuring the efficiency of the vertex cache under different mesh optimization algorithms. The ACMR is basically the number of vertex transforms divided by the number of primitives, and greatly depends on the topology of the mesh. For a triangle mesh the theoretical optimal is 0.5, but if the mesh has boundaries, or disconnected triangles, then the optimal value is much higher. So, you have to compare the ACMR against the vertex to triangle ratio of the mesh.

I think that a better way of measuring how well a mesh optimization algorithm or a cache implementation performs is using the average transform to vertex ratio (ATVR), that is, the number of vertex transforms divided by the number of vertices. In the optimal case it’s always 1, independently of the mesh and the primitive type. I think it provides a much more intuitive a much more intuitive idea of the cost of rendering a mesh. For example, if the transform to vertex ratio is 2, it means that each vertex is transformed an average of 2 times.

Here’s another example: In his article about Vertex Cache Optimisation, Tom Forsyth has to clarify that the results for the GrannyRocks mesh (between 0.797 and 0.765) are actually quite good, because the best ACMR possible is 0.732. That clarification would not be necessary when using the metric that I propose. Instead, you would say that the transform to vertex ratio is between 1.09 and 1.05, and it’s instantly obvious that it’s a good result.