Custom interface for rendering subtitles on an RGBA texture(s) | (XySubFilter for madVR) [Part 1]

[GoogleCodeExporter]

This is a kind of feature request. Fot the info you better see the link beliw, 
since I don't feel like past all conversation here.
http://forum.doom9.org/showthread.php?p=1535165#post1535165

Original issue reported on code.google.com by yakits...@gmail.com on 30 Oct 2011 at 6:08

• Merged into: #91

[GoogleCodeExporter]

And further more, I found something like this:

DXPMSAMPLE — A structure with red, green, blue, and alpha components, each 
having 8 bits. The color channels are premultiplied by the alpha component for 
this type.

http://msdn.microsoft.com/en-us/library/aa753543%28v=vs.85%29.aspx

Does it help for using pre-multiplied alpha on GPU?

Original comment by YuZhuoHu...@gmail.com on 29 Nov 2011 at 1:27

[GoogleCodeExporter]

I fixed my code, its only one division (per pixel), and not one per iteration, 
however for precision it should be calculated in floating point or at least 
16-bit integer, and not in 8-bit integer, of course.

 RGBbig = Abig = 0
 foreach(subpic)
   RGBbig = (RGBbig * (1-Asub) + RGBsub * Asub)
   Abig = (1 - ((1-Abig) * (1-Asub))
 end
 RGBbig = RGBbig / Abig

> I do no serious test, but I am quite positive that do A1*B1+A2 using MMX/SSE2 
would be faster than A1*B1+A2*B2.

A1*B1+A2*B2 is one SSE2 instruction, and processes up to 4 16-bit pixels at the 
same time. Implementing A1*B1+A2 would probably end up being A1*B1+A2*1, just 
so that the same instruction could be used.

I'm not sure why you insist on pre-multiplied alpha, i'm still not convinced of 
any advantages, if anything i see a complexity there which could just be 
avoided. Handing around normal ARGB32 bitmaps is easier to understand and 
handle. I still have my use-case of blending it onto a YUV video, where i would 
have to un-multiply the alpha before conversion, or it might end up being 
rather weird.

> So the reason why using a maxNumBitmaps option not combineBitmaps, is we 
won't lose anything by using maxNumBitmaps.

We also don't gain anything. Why would a renderer support rendering 100 small 
bitmaps, but not 101? I just don't see the advantage. Either you can process 
multiple small bitmaps, or you cannot. If you want to make the Alpha topic 
easier, just remove the ability for the sub-renderer to merge the images 
completely, and always let the consumer do that - that way there are no 
misunderstandings.

Original comment by h.lepp...@gmail.com on 29 Nov 2011 at 1:39