GPU acceleration in Krita

[Andrew Savonichev]

Hi Dmitry,

> Could you try to compare the numbers with our main benchmark?
>
> It is placed in:
> libs/ui/tests/FreehandStrokeBenchmark

Right now, the OpenCL version is 30% slower than the optimized CPU
version. There is also some stability issue when the benchmark runs on 7
cores.

CPU (testDefaultTip):
    Cores: 1 Time: 116407 (ms)
    Cores: 2 Time: 59840 (ms)
    Cores: 3 Time: 40105 (ms)
    Cores: 4 Time: 30475 (ms)
    Cores: 5 Time: 28310 (ms)
    Cores: 6 Time: 29824 (ms)
    Cores: 7 Time: 28373 (ms)
    Cores: 8 Time: 27611 (ms)

GPU (testDefaultTip):

    Cores: 1 Time: 140742 (ms)
    Cores: 2 Time: 88972 (ms)
    Cores: 3 Time: 57054 (ms)
    Cores: 4 Time: 42305 (ms)
    Cores: 5 Time: 39679 (ms)
    Cores: 6 Time: 37384 (ms)
    <out of resources>

--
Andrew