3 ms·

Neat. Isn't this akin to 400k triangles on a GPU? So as long as you do instancing it doesn't seem too difficult (performance wise) in itself. Even if there are

by juancn 4y ago

Neat. Isn't this akin to 400k triangles on a GPU? So as long as you do instancing it doesn't seem too difficult (performance wise) in itself. Even if there are many sprites, texture mapping should solve for the taking pixels to the screen part. My guess is that the rendering is not the hardest part, although it's kinda cool.

deleted 4y ago
[deleted]
chrisseaton 4y ago
> Isn't this akin to 400k triangles on a GPU? Is it faster to render two triangles with slightly less area, or one triangle with slightly more area, to draw the same sprite?
- iliketrains 4y ago
  Rendering only one large triangle can be faster than two. First one triangle needs less memory, less vertex processing, etc. Second, modern GPUs render pixels in groups of 2x2 up to 8x8 "tiles". If only one pixel from this group is part of a triangle, the entire group will be rendered. When two triangles form a quad, the entire area along the diagonal "seam" will be rendered twice. The smaller quads you have, the more overhead. Also see https://www.saschawillems.de/blog/2016/08/13/vulkan-tutorial-on-rendering-a-fullscreen-quad-without-buffers/ https://www.saschawillems.de/blog/2016/08/13/vulkan-tutorial...
  - HWR_14 4y ago
    I disagree, with the exception of the case you link to where half the pixels are outside the viewport or maybe where a sufficient percentage are outside the viewport. > When two triangles form a quad, the entire area along the diagonal "seam" will be rendered twice This may be true, but I'm pretty sure that this is more than made up for by the additional pixels in the single triangle circumscribing the quad. In fact, I'm willing to bet that it's a mathematical certainty for any rectangle, although I didn't do enough of the math to prove it. Instead, I would say that most rendering, especially of hundreds of thousands of 2D shapes, are going to be pixel limited. So trading pixels for vertices is a poor trade.
    - gmueckl 4y ago
      It depends on the size of the sprites in this case. Small sprites will benefit from being drawn as single triangles. These "shadow" pixel shader invocations are a very real pain when it comes to rendering highly detailed models. The hardware rasterization pipeline can't cope well with huge amounts of really tiny triangles. That's the reason why UE5 Nanite uses a software GPU rasterizer for the high geometry density sections of a model - it's faster! Large area primitives will be rendered normally AFAIK.
- juancn 4y ago
  Honestly I'm not sure. I don't think that at 200k or 400k level will matter much. Math is probably easier on humans if you think about the sprites as rectangular (so two triangles), but you could in principle make each sprite a triangle, and texture map in a shader a rectangular area of the triangle.
- quadcore 4y ago
  Pretty sure overdraw / fillrate bottlenecks before vertex processing. Also you could draw that quad using strips which would then amount for only one more processed vertex compared to triangle. Edit: okay surely with modern architecture there is no pixel write because of some early alpha cut but you still have to fetch the texture to make it so texture fetch (memory) will bottleneck first. I guess.
  - chrisseaton 4y ago
    By this argument you should higher performance from higher-poly models... which clearly isn't the case?
    - quadcore 4y ago
      Oh, let me clear that for you. The trick discussed here is that you can draw a sprite (a quad) using one large triangle. The sprite is just inside it but the triangle has quite some "wasted" surface.
      - chrisseaton 4y ago
        Right, so if you're rendering a sphere, it'd make sense to use lots of triangles to get a smoother surface and less overdraw in order to render more quickly, but that doesn't seem to be the case in reality as people use lower-poly meshes (with more overdraw) if they want it to be quicker.
        quadcore 4y ago
        Well there is a specific tradeoff involved in this particular case, i.e. one more processed vertex versus something like +100% added surface, if my triangle maths are still what they were.
  - Jasper_ 4y ago
    You shouldn't use strips, they're slower than triangle lists on most GPUs. If by alpha cut you mean "discard", that's going to be much slower than two triangles. Two triangles will have a tiny bit of quad overshading on the seam, compared to a full extra triangle's worth in the alpha cut case.

by juancn 4y ago

deleted 4y ago

[deleted]

chrisseaton 4y ago

> Isn't this akin to 400k triangles on a GPU? Is it faster to render two triangles with slightly less area, or one triangle with slightly more area, to draw the same sprite?

iliketrains 4y ago
Rendering only one large triangle can be faster than two. First one triangle needs less memory, less vertex processing, etc. Second, modern GPUs render pixels in groups of 2x2 up to 8x8 "tiles". If only one pixel from this group is part of a triangle, the entire group will be rendered. When two triangles form a quad, the entire area along the diagonal "seam" will be rendered twice. The smaller quads you have, the more overhead. Also see https://www.saschawillems.de/blog/2016/08/13/vulkan-tutorial-on-rendering-a-fullscreen-quad-without-buffers/ https://www.saschawillems.de/blog/2016/08/13/vulkan-tutorial...
- HWR_14 4y ago
  I disagree, with the exception of the case you link to where half the pixels are outside the viewport or maybe where a sufficient percentage are outside the viewport. > When two triangles form a quad, the entire area along the diagonal "seam" will be rendered twice This may be true, but I'm pretty sure that this is more than made up for by the additional pixels in the single triangle circumscribing the quad. In fact, I'm willing to bet that it's a mathematical certainty for any rectangle, although I didn't do enough of the math to prove it. Instead, I would say that most rendering, especially of hundreds of thousands of 2D shapes, are going to be pixel limited. So trading pixels for vertices is a poor trade.
  - gmueckl 4y ago
    It depends on the size of the sprites in this case. Small sprites will benefit from being drawn as single triangles. These "shadow" pixel shader invocations are a very real pain when it comes to rendering highly detailed models. The hardware rasterization pipeline can't cope well with huge amounts of really tiny triangles. That's the reason why UE5 Nanite uses a software GPU rasterizer for the high geometry density sections of a model - it's faster! Large area primitives will be rendered normally AFAIK.
juancn 4y ago
Honestly I'm not sure. I don't think that at 200k or 400k level will matter much. Math is probably easier on humans if you think about the sprites as rectangular (so two triangles), but you could in principle make each sprite a triangle, and texture map in a shader a rectangular area of the triangle.
quadcore 4y ago
Pretty sure overdraw / fillrate bottlenecks before vertex processing. Also you could draw that quad using strips which would then amount for only one more processed vertex compared to triangle. Edit: okay surely with modern architecture there is no pixel write because of some early alpha cut but you still have to fetch the texture to make it so texture fetch (memory) will bottleneck first. I guess.
- chrisseaton 4y ago
  By this argument you should higher performance from higher-poly models... which clearly isn't the case?
  - quadcore 4y ago
    Oh, let me clear that for you. The trick discussed here is that you can draw a sprite (a quad) using one large triangle. The sprite is just inside it but the triangle has quite some "wasted" surface.
    - chrisseaton 4y ago
      Right, so if you're rendering a sphere, it'd make sense to use lots of triangles to get a smoother surface and less overdraw in order to render more quickly, but that doesn't seem to be the case in reality as people use lower-poly meshes (with more overdraw) if they want it to be quicker.
      - quadcore 4y ago
        Well there is a specific tradeoff involved in this particular case, i.e. one more processed vertex versus something like +100% added surface, if my triangle maths are still what they were.
- Jasper_ 4y ago
  You shouldn't use strips, they're slower than triangle lists on most GPUs. If by alpha cut you mean "discard", that's going to be much slower than two triangles. Two triangles will have a tiny bit of quad overshading on the seam, compared to a full extra triangle's worth in the alpha cut case.