[Bf-committers] texture painting blend mode patch

Fredrik hansson fredrikhansson_12345 at yahoo.com
Thu Nov 1 20:33:54 CET 2012

converted the code from 8bit -> float didn't do any of that optimizing should perhaps do that but i preferred to just get it working quickly and without getting any additional errors.

i did notice a few things however while testing out the code.
mainly that it felt like it always were in air brush mode making some of the brushes way to strong unless you had a huge spacing (not overlapping).
as for if the hsv_to_rgb crashes well it did when i originally wrote the patch but just looked at the code and i see no reason at all for it to actually crash as you said its just 2 simple static functions.

 From: Xavier Thomas <xavier.thomas.1980 at gmail.com>
To: Fredrik hansson <fredrikhansson_12345 at yahoo.com>; bf-blender developers <bf-committers at blender.org> 
Sent: Wednesday, October 31, 2012 8:25 PM
Subject: Re: [Bf-committers] texture painting blend mode patch

I a looked at the patch and effectively the code for float images is missing.

Another thing that might need investigating is the rgb_to_hsv and hsv_to_rgb method,  basically duplicated code because the origiginal version crash with threading! I think it might be better to fix the original, it should be basic static methods, I do no see any reason to crash.

Not related to this patch specifically but it seems there is quite a room for optimisation. If I understood well, for each pixel that is painted on, IMB_blend_color() is called, and this function is only a big switch(blend_mode) that then call the method that blend the 2 colors.

One possibly better way to do this is to cache a pointer to the apropriate method each time the blend mode is changed so the huge switch statement is not done for every pixel.
Another way maybe to inline the blend funtions so we do a function call less for each pixel.

For the float version of the blend funtion SSE2 will certainly provide a 20 to 40% gain, and (depending on the compilator and the images used) you might want to avoid code like this:

    temp=big float calculation;
    temp=other big float calc;

which is not pipeline friendly, and prefer:

temp1 = big float calculation;

temp2 = other big float calc;

temp = test ? temp1 : temp2;

but this is not always the case so don't optimise blindly.


2012/10/31 Fredrik hansson <fredrikhansson_12345 at yahoo.com>

> right i think that might have been why it wasn't added before or
>something i guess i could take a look at writing the float versions
>quickly should be the same pretty much.
> From: Antony Riakiotakis <kalast at gmail.com>
>To: Fredrik hansson <fredrikhansson_12345 at yahoo.com>; bf-blender developers <bf-committers at blender.org>
>Sent: Wednesday, October 31, 2012 4:39 PM
>Subject: Re: [Bf-committers] texture painting blend mode patch
>This looks cool! A little remark though, we would also need float
>versions for the functions to support float images properly.
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