5 ms·

This is an exciting demonstration, but I have one worry that's unaddressed: I'm assuming all the other nitpicky details of hinted font rendering etc is handled

This is an exciting demonstration, but I have one worry that's unaddressed: I'm assuming all the other nitpicky details of hinted font rendering etc is handled correctly by all the renderers compared? I mean, they all provide pixel-identical output? Otherwise the point is mostly useless. A faster rendering implementation is almost useless if the output doesn't look as nice. I wouldn't care if the text I'm reading over 5 minutes takes 200ms vs 800ms to render.

leni536 10y ago
I think one can mix hinters and renderers from different libraries. If it's all about fast vector rendering I don't see why they couldn't just use freetype's hinter (maybe they do).
- a_e_k 10y ago
  You can. For my programming font [0], I provide versions of it that bake in the output from Freetype's hint interpreter applied at different point sizes and display DPIs. This way platforms such as macOS that don't always apply hinting can show it as though they did. [0] http://eastfarthing.com/luculent/ http://eastfarthing.com/luculent/
pcwalton 10y ago
Pathfinder's rendering is best-in-class, equaling or exceeding the quality of the other renderers. FreeType, stb_truetype, font-rs, and Pathfinder all use exact trapezoidal area calculations for antialiasing. Most GPU algorithms use lower-quality multisample antialiasing, but matching the system renderer in quality is one of the key goals of Pathfinder. Regarding hinting, hinting is mostly a transformation applied to the vectors before rasterization, so it's (again, mostly) independent of the actual vector rasterizer. Note that many systems do no hinting at all. To make the benchmarks fair, hinting was disabled for the libraries that support it.
- ComputerGuru 10y ago
  Having done some work that involved comparing a number of text rendering libraries in the past, I'm aware of the minute differences in rendering and hinting (even when the output should be the same). Could you briefly mention how hinting here would compare to ClearType?
  - pcwalton 10y ago
    Hinting and subpixel AA (ClearType) are separate features. Could you elaborate?
    - 21 10y ago
      The parent might mean ClearType in the sense of the Windows ClearType renderer, which is pretty strongly hinted in general.
      - ComputerGuru 10y ago
        Yes, thank you. Is there any other ClearType? On Windows, CT is a combination of both heavy hinting and configurable subpixel aliasing.
- a_e_k 10y ago
  I've been planning lately on writing my own little 2d rasterizer for fun. While I really like the trapezoidal signed-area method, when reading STB's write-up I noticed that it can overestimate coverage when a path self-intersects or when subpaths intersect. Does Pathfinder solve this? Between that and clipping paths, I've been thinking of sticking with multisampling, as nice as the exactness of the trapezoidal algorithm can be.
  - pcwalton 10y ago
    Pathfinder doesn't do anything special in that case; it has the same limitations as stb_truetype. There's probably a way to fix these issues if they come up in practice. I would recommend doing the trapezoidal area approach in spite of these limitations. Having 256 shades of gray instead of 8 or so makes a big difference for all paths, not just pathological ones. It often ends up faster than MSAA, too.
flukus 10y ago
> I mean, they all provide pixel-identical output? I wonder if this is even possible once you move it to the GPU. Reading about some of the fingerprinting methods in browsers lately, many rely on different GPU's doing different things with the same input.
- pcwalton 10y ago
  > I wonder if this is even possible once you move it to the GPU. Different GPUs should produce pixel-identical output. If not, it's a bug either in Pathfinder or the driver.
  - JoshTriplett 10y ago
    Can you provide some rendered screenshots with a few fonts and sizes? (Ideally including a side-by-side comparison with Freetype?)
  - vvanders 10y ago
    In theory yes, in practice that almost never happens. The number of teams I've seen pursue golden-image tests on GPU pipelines and fail has been 100%(4/4).
    - dgfgfdagasdfgfa 10y ago
      What's the source of the image differences? I probably shouldn't find this disturbing, but I do.
      - vvanders 10y ago
        It's a host of things, generally I've seen: - Poorly defined APIs/types that allow vendors to diverge. - Legit driver bugs. - Vendors preferring optimizations to following the spec(including skipping memzero requirements). - Hardware that doesn't behave how it should(fp32 falling back to fp16 silently for instance). Overall you don't really win any points in the market for correctness, instead performance and efficiency are highly valued.

leni536 10y ago

I think one can mix hinters and renderers from different libraries. If it's all about fast vector rendering I don't see why they couldn't just use freetype's hinter (maybe they do).

a_e_k 10y ago
You can. For my programming font [0], I provide versions of it that bake in the output from Freetype's hint interpreter applied at different point sizes and display DPIs. This way platforms such as macOS that don't always apply hinting can show it as though they did. [0] http://eastfarthing.com/luculent/ http://eastfarthing.com/luculent/

pcwalton 10y ago

Pathfinder's rendering is best-in-class, equaling or exceeding the quality of the other renderers. FreeType, stb_truetype, font-rs, and Pathfinder all use exact trapezoidal area calculations for antialiasing. Most GPU algorithms use lower-quality multisample antialiasing, but matching the system renderer in quality is one of the key goals of Pathfinder. Regarding hinting, hinting is mostly a transformation applied to the vectors before rasterization, so it's (again, mostly) independent of the actual vector rasterizer. Note that many systems do no hinting at all. To make the benchmarks fair, hinting was disabled for the libraries that support it.

ComputerGuru 10y ago
Having done some work that involved comparing a number of text rendering libraries in the past, I'm aware of the minute differences in rendering and hinting (even when the output should be the same). Could you briefly mention how hinting here would compare to ClearType?
- pcwalton 10y ago
  Hinting and subpixel AA (ClearType) are separate features. Could you elaborate?
  - 21 10y ago
    The parent might mean ClearType in the sense of the Windows ClearType renderer, which is pretty strongly hinted in general.
    - ComputerGuru 10y ago
      Yes, thank you. Is there any other ClearType? On Windows, CT is a combination of both heavy hinting and configurable subpixel aliasing.
a_e_k 10y ago
I've been planning lately on writing my own little 2d rasterizer for fun. While I really like the trapezoidal signed-area method, when reading STB's write-up I noticed that it can overestimate coverage when a path self-intersects or when subpaths intersect. Does Pathfinder solve this? Between that and clipping paths, I've been thinking of sticking with multisampling, as nice as the exactness of the trapezoidal algorithm can be.
- pcwalton 10y ago
  Pathfinder doesn't do anything special in that case; it has the same limitations as stb_truetype. There's probably a way to fix these issues if they come up in practice. I would recommend doing the trapezoidal area approach in spite of these limitations. Having 256 shades of gray instead of 8 or so makes a big difference for all paths, not just pathological ones. It often ends up faster than MSAA, too.

flukus 10y ago

> I mean, they all provide pixel-identical output? I wonder if this is even possible once you move it to the GPU. Reading about some of the fingerprinting methods in browsers lately, many rely on different GPU's doing different things with the same input.

pcwalton 10y ago
> I wonder if this is even possible once you move it to the GPU. Different GPUs should produce pixel-identical output. If not, it's a bug either in Pathfinder or the driver.
- JoshTriplett 10y ago
  Can you provide some rendered screenshots with a few fonts and sizes? (Ideally including a side-by-side comparison with Freetype?)
- vvanders 10y ago
  In theory yes, in practice that almost never happens. The number of teams I've seen pursue golden-image tests on GPU pipelines and fail has been 100%(4/4).
  - dgfgfdagasdfgfa 10y ago
    What's the source of the image differences? I probably shouldn't find this disturbing, but I do.
    - vvanders 10y ago
      It's a host of things, generally I've seen: - Poorly defined APIs/types that allow vendors to diverge. - Legit driver bugs. - Vendors preferring optimizations to following the spec(including skipping memzero requirements). - Hardware that doesn't behave how it should(fp32 falling back to fp16 silently for instance). Overall you don't really win any points in the market for correctness, instead performance and efficiency are highly valued.