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wu_pixel small optimization
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5% faster
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@softhack007
softhack007 committed Sep 29, 2024
1 parent 10d8cfd commit d3c401e
Showing 1 changed file with 5 additions and 2 deletions.
7 changes: 5 additions & 2 deletions wled00/FX_2Dfcn.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -704,11 +704,14 @@ void Segment::wu_pixel(uint32_t x, uint32_t y, CRGB c) { //awesome wu_pixel
WU_WEIGHT(ix, yy), WU_WEIGHT(xx, yy)};
// multiply the intensities by the colour, and saturating-add them to the pixels
for (int i = 0; i < 4; i++) {
CRGB led = getPixelColorXY((x >> 8) + (i & 1), (y >> 8) + ((i >> 1) & 1));
int wu_x = (x >> 8) + (i & 1); // precalculate x
int wu_y = (y >> 8) + ((i >> 1) & 1); // precalculate y
CRGB led = getPixelColorXY(wu_x, wu_y);
CRGB oldLed = led;
led.r = qadd8(led.r, c.r * wu[i] >> 8);
led.g = qadd8(led.g, c.g * wu[i] >> 8);
led.b = qadd8(led.b, c.b * wu[i] >> 8);
setPixelColorXY(int((x >> 8) + (i & 1)), int((y >> 8) + ((i >> 1) & 1)), led);
if (led != oldLed) setPixelColorXY(wu_x, wu_y, led); // don't repaint if same color

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@DedeHai

DedeHai Sep 30, 2024 •
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precalculation is done even if this condition is false. What is the point of the precalculation? the compiler will probably drop those.
edit:
disregard that, I just now realised the value is used twice...
}
}
#undef WU_WEIGHT
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5 comments on commit d3c401e

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@blazoncek, in principle, wu_pixel could be modified to use uint32_t color instead of CRGB. Basically we would simply replicate line 713 for the W channel. 🤔 But not sure if that's worth it ... what do you think?

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@softhack007 softhack007 commented on d3c401e Sep 29, 2024 •
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@DedeHai I've just "rediscovered" this old function, which performs setPixelColor with 256 subpixels very accurately and fast.
I was wondering if that's useful for your particle effect PR #3823 ?

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wu_pixel could be modified to use uint32_t color instead of CRGB

Of course. I just ported it from FastLED examples with as little effort I managed.

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@DedeHai DedeHai commented on d3c401e Sep 30, 2024 •
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I did look at the 'wu algorithm' a while back, need to check my notes for details but IIRC I found it to be ill-suited for the particle system (but it does almost the same thing). With knowledge gained from all the optimization work I did recently I may revisit the topic though.
Regarding white channel: my take on this is still that 2D setups very rarely (at least currently) use RGBW pixels, palettes do not use any white channel either. I still do not fully understand, where the white channel is even used in rendering (before white channel calculation, which is done at bus level if I am not mistaken).
I would be in favour a solution that drops the white channel completely and use an alpha channel instead.
EDIT:
if you want to add white channel support: this would be a good opportunity to use the CRGBW struct I added in the speed improvements PR.

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White channel is only used in one effect if memory serves me well. Not sure in which.
I am in favour of ditching W or replace it with alpha.

If anyone wants to reduce power usage by utilising W channel he/she can do with auto-white calculation.

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