[PATCH 5/5] d2d1: Implement initial support for quadratic bezier outlines.

[Henri Verbeet]

On 21 May 2017 at 18:23, Dmitry Timoshkov <dmitry at baikal.ru> wrote:
> Henri Verbeet <hverbeet at codeweavers.com> wrote:
>
>> +static void d2d_point_lerp(D2D1_POINT_2F *out,
>> +        const D2D1_POINT_2F *a, const D2D1_POINT_2F *b, float t)
>> +{
>> +    out->x = a->x * (1.0f - t) + b->x * t;
>> +    out->y = a->y * (1.0f - t) + b->y * t;
>> +}
>
> According to my investigation of a better bilinear blending (lerp)
> implementation the above formula is better to explicitely simplify
> to
>
> out->x = a->x + (b->x - a->x) * t;
> out->y = a->y + (b->y - a->y) * t;
>
For performance, quite possibly. This isn't particularly performance
sensitive code though, and I'd be surprised if that variant had better
accuracy.

> or even better to avoid floating point operations at all by replacing
> them either by fixed point math or a mmx/sse helper, which is able
> to considerably (x10) improve performance.
>
Yes, for performance sensitive code we'd want to use SSE intrinsics.
There are places in d3dx9 where that would certainly be worthwhile.