This sample attempts to re-create an image's alpha channel by drawing it
one pixel at a time and timing how long each pixel takes to draw.
The "abc" text should appear twice normally, and the third and fourth
versions are reconstructed from timing, one by timing 1:1 pixel draws,
the other by timing 1x1:1024x1024 upscale into an offscreen. It's not
meant to be an exact reconstruction, but you can easily see the shapes,
particularly at -O0, -O1, and -Os. Auto-vectorization from -O2/-O3 do
a good amount to cover up the problem.
The legacy CPU backend is the main place to look. I haven't been able
to reconstruct any images using SkRasterPipelineBlitter or SkVMBlitter,
and while on the GPU I do see non-random patterns in the timing, it
appears to be the same single pattern across devices, OSes, GPUs, GPU
APIs and content... I assume it's something like our resource caching
policy.
This can't really be a GM, given how it draws non-deterministically.
Bug: chromium:1088224
Change-Id: I2ec79c8dd407ecb104fd9bf0c8039cb6dd1fe436
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/313466
Commit-Queue: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Reed <reed@google.com>
5c612ade3b