How does cache work with tile based rendering?

Are there any tips on how to improve cache hit ratio for it? (for instance, if tiles are processed horizontally and I have vertical segments of triangles with the same texture, does it work worse for cache than if I had triangles layout out horizontally?)

  • 1
    $\begingroup$ What do you mean by vertical vs horizontal layout of triangles? $\endgroup$
    – Mokosha
    Aug 28, 2015 at 4:04
  • $\begingroup$ @Mokosha sorry, this somehow got unnoticed to me. I just saw it now. This is more a theoretical than pratical question and I don't even know if this makes sense now. Anyway, what I meant was, say a triangle intersect tiles (x, y) and (x+1, y) and that the these two tiles get processed one after another. Would that be a better for texture cache than If I had a triangle intersecting (x, y) and (x, y+1)? (Because of the border pixels and the layout of triangles not being in the same direction the tiles processing is) $\endgroup$ Sep 2, 2015 at 13:06

1 Answer 1


Whether it's a tile based GPU or not doesn't really affect the texture cache architecture. The memory layout of texture will look like some flavor of Morton order or Hilbert curve in all GPUs.

As a result, it's more efficient to render triangles that are close to equilateral triangles because GPU memory system fetches cache lines of texels.

So obviously on tile borders, it may happen that you have to fetch texels twice. This has a small cost as tile borders are only "few" pixels.

Arguably desktop GPUs behave identically to tile based GPUs as experiments such as the following demonstrate: http://www.g-truc.net/post-0597.html

The size of the tiles differ but both architecture actually process fragments into a hierarchy of tiles of different sizes.

When coding for tile based GPUs my recommendation is to always have in mind:

  1. Don't switch framebuffer objects unless you really need to.
  2. When binding a new framebuffer object, if you don't need to save the content of the current framebuffer, discard it. If don't want to load content of the new framebuffer, then you should clear the framebuffer.
  • $\begingroup$ I updated the second item as the edit wasn't what I meant. Otherwise, it looks great! $\endgroup$
    – Christophe
    Sep 1, 2015 at 23:15
  • $\begingroup$ Hi Christophe, did you mean "equilateral" triangles rather than "isosceles"? Rather than "Hilbert" I'd have said "Morton" order as the addressing is much easier in hardware. $\endgroup$
    – Simon F
    Sep 2, 2015 at 11:04
  • $\begingroup$ @Christophe thanks! This is really helpfull. So, for the border pixels, doesn't texture cache matter? That's was kind of what I was wondering. So, If I have a triangle that intersects tiles (x, y) and (x+1, y) and GPU just rasterized tile (x, y). Assuming tile (x+1, y) will be next, even if a different Execution Units processes it, won't I benefit from texture cache when sampling texels for this triangle? $\endgroup$ Sep 2, 2015 at 12:57
  • $\begingroup$ Also, I got curious about the Hilbert pattern. I always assumed this was true for block compressed textures. Is this true for all textures? PS: I also didn't follow the last paragraph. $\endgroup$ Sep 2, 2015 at 13:00
  • $\begingroup$ PVRTC encodes texture blocks in a morton order $\endgroup$ Sep 7, 2015 at 19:09

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