[FFmpeg-devel] [PATCH] lavfi/testsrc2: fix completely transparent alpha.

Carl Eugen Hoyos ceffmpeg at gmail.com
Tue Jul 25 10:18:34 EEST 2017

2017-07-24 13:02 GMT+02:00 Nicolas George <george at nsup.org>:
> Le sextidi 6 thermidor, an CCXXV, Carl Eugen Hoyos a écrit :
>> > Oh, you mean a gradient on the alpha channel. It is not really possible
>> > without making the code more complex and I think significantly slower.
>> > A coarse gradient between the different vertical bands is easy, but the
>> > alpha must be constant in each band, just like the color.
>> (Why?)
> Because memset() is faster and simpler than anything else that could do
> the work.

I thought that one of my suggestions (alpha_value = y * 255 / height)
would play nice with memset().

> testsrc2 is based on the drawutils functions, which provide a
> few drawing primitives, especially rectangles. They are limited in
> features but are fast and support many pixel formats with little code.
>> Any change that provides different transparency values on one frame is
>> a useful fix for a long-standing bug / missing feature imo.
> Note that with the current patch, while most of the drawing has constant
> alpha, the beating cross and bouncing square ball are fully opaque, so
> there are already two alpha values. It is better than nothing.


> I suggest we apply the patch as is, since it allows the overlay test to
> move forward. And then we can consider how to add an interesting alpha
> channel for better testing.

> Is it ok with you?

I am ok with everything that improves the current situation, I just
wanted to point out a long-standing issue when I saw your patch.

I cannot comment on the Plasma generator.

Carl Eugen

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