imageproc | Image processing operations | Computer Vision library

The rusttype repo contains an example (examples/image.rs), which measures the bounds of a line of text and renders it to an image. Basically what you're searching, besides the centering part.

I was able to get all of the drawing (creating the grid and the text) down to 4-5ms by:

• Caching values where possible (Random, StringFormat, Math.Pow)
• Using ArrayPool for scratch buffer
• Using the DrawString overload accepting a StringFormat with the following options:
  • Alignment and LineAlignment for centering (in lieu of manually calculating)
  • FormatFlags and Trimming options that disable things like overflow/wrapping since we are just writing small numbers (this had an impact, though negligible)
• Using a custom Font from the GenericMonospace font family instead of SystemFonts.DefaultFont
  • This shaved off ~15ms
• Fiddling with various Graphics options, such as TextRenderingHint and SmoothingMode
  • I got varying results so you may want to fiddle some more
• An array of Color and the ToArgb function to create an int representing the 4x bytes of the pixel's color
• Using LockBits, (semi-)unsafe code and Span to
  • Fill a buffer representing 1px high and size * countpx wide (the entire image width) with the int representing the ARGB values of the random colors
  • Copy that buffer size times (now representing an entire square in height)
  • Rinse/Repeat
  • unsafe was required to create a Span<> from the locked bit's Scan0 pointer
• Finally, using GDI/native to draw the text over the graphic

I was then able to shave a little bit of time off of the actual saving process by using the Image.Save(Stream) overload. I used a FileStream with a custom buffer-size of 16kb (over the default 4kb) which seemed to be the sweet spot. This brought the total end-to-end time down to around 40ms (on my machine).

I think the best way is to know where pixels are not black