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‘tis a beautiful summer’s day...
All is well, every bird is singing, and three venerable old gentlemen are gathered in the splendid garden of their retirement home. And, a question pops up:
“What is the fastest thing in Universe?”
“But everybody knows the answer to that! It is light. Nothing can travel faster than light. Einstein even provided mathematical proof.”
“Delusions, delusions! It is thought. My thought can travel from this hammock, to the Andromeda galaxy – millions of light years away – in a blink. That is countless of magnitudes faster.”
“Ah my dearest friends... have you learnt nothing? The fastest thing, in Universe, is crap.”
“Crap?”
“Crap??”
“But yes of course! I can can crap meself, before even thinking at all.”
.Coat? Oh! Dear Heavens, where on Earth did I leave my coat?
"If we don't change direction, we'll end up where we're going"
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For this one, you will not even have time to grab your coat.
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megaadam wrote: Coat? Oh! Dear Heavens, where on Earth did I leave my coat?
Your coate (and yourselfe) were deposited in the streete before you started telling your olde joke. 
Freedom is the freedom to say that two plus two make four. If that is granted, all else follows.
-- 6079 Smith W.
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Wordle 1,209 3/6
⬜🟩⬜🟨⬜
⬜🟩⬜🟩🟩
🟩🟩🟩🟩🟩
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Wordle 1,209 4/6*
⬜⬜🟨⬜🟩
🟨🟨⬜⬜🟩
⬜🟩🟩⬜🟩
🟩🟩🟩🟩🟩
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Wordle 1,209 2/6
🟩🟨🟨⬜🟩
🟩🟩🟩🟩🟩
In a closed society where everybody's guilty, the only crime is getting caught. In a world of thieves, the only final sin is stupidity. - Hunter S Thompson - RIP
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Wordle 1,209 4/6*
🟨🟨⬜⬜🟩
⬜⬜🟨🟨🟩
🟨🟩⬜⬜🟩
🟩🟩🟩🟩🟩
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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Wordle 1,209 2/6
🟨🟩⬜🟨⬜
🟩🟩🟩🟩🟩
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Wordle 1,209 4/6
🟨⬛⬛🟨🟩
⬛⬛🟩🟨🟩
🟩🟩🟩⬛🟩
🟩🟩🟩🟩🟩
Ok, I have had my coffee, so you can all come out now!
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I'm not sure if this will bear any fruit, but I'm asking on the off chance someone might know what I am going on about below.
I understand alpha-blending (pixels w/ opacity)
I don't understand compositing modes
They are something like these, but in my codebase they are not called this.
Blend modes - Wikipedia[^]
static const composition_function_t composition_solid_table[] = {
composition_solid_source,
composition_solid_source_over,
composition_solid_destination_in,
composition_solid_destination_out,
};
static const composition_function_t composition_table[] = {
composition_source,
composition_source_over,
composition_destination_in,
composition_destination_out,
};
These are the blend/compositing modes as they appear in my codebase.
The implementation of those functions is here, in case anyone's interested
plutovg/source/plutovg-blend.c at main · sammycage/plutovg · GitHub[^]
I need to adapt them so I need to understand them. I've tried following the code, but obviously I'm not doing it right because when I try to adapt it to do read/writes to RGB565 bitmaps some of my colors are coming back wrong.
For the most part I am using "composition_solid_source" and composition_solid_source_over" and the "source over" is what is confusing to me. I don't know what that means.
Any graphics afficionados/nadas be able to explain this to me in high level terms?
Check out my IoT graphics library here:
https://honeythecodewitch.com/gfx
And my IoT UI/User Experience library here:
https://honeythecodewitch.com/uix
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I use Photoshop v7 (2002) and only in the simplest of ways really, so I don't think I can help you. Though I will if I can.
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I think I grok Photoshop quite well. I think the Wiki does a fine job of explaining the plethora of blend modes.
All PS blend modes produce one resulting RGBA layer, from two RGBA layers in.
It seems to me, after (possibly too) quick glance, that the functions you point to, take one RGBA in.
I assume you know this: The multiplication of R * R is not a direct integer MUL. It is a "normalised" MUL.
i.e. 0x80 * 0x80 is not 0x4000 it must be seen as 0.5 * 0.5 == 0.25
"If we don't change direction, we'll end up where we're going"
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Sorry if this sounds dumb but, how can 0x80 become 0.5 ?
In a closed society where everybody's guilty, the only crime is getting caught. In a world of thieves, the only final sin is stupidity. - Hunter S Thompson - RIP
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0x80 is 128 which is half of 256, which is a byte.
I have a function called BYTE_MUL() in my code that does multiplication by 1/255 of a value, in which case 0x80 is about half.
Check out my IoT graphics library here:
https://honeythecodewitch.com/gfx
And my IoT UI/User Experience library here:
https://honeythecodewitch.com/uix
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That's what I assumed was happening but didn't know for sure - thanks for clarifying
In a closed society where everybody's guilty, the only crime is getting caught. In a world of thieves, the only final sin is stupidity. - Hunter S Thompson - RIP
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The important bit was the first part "two input layers for Photoshop blending". I saw a function with only one input layer.
The 0x80 was just a safety check. I assumed you knew, and you did, so yes:
0xff == 255/255, 0x80 == 128/255 ≈ 1/2, 0x01 == 1/255
"If we don't change direction, we'll end up where we're going"
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In photoshop, you can superpose different layers, and decide for each how it will "blend" with the layers below.
The simplest blend way is to simply superpose the layer content, so you see at first what is on the layer on top, then what is on the layer below it but for what is on the first layer, and so on. Like a pile of cards that are not aligned, you'll see the top card and bits of the cards below it if you look from above.
And then you can apply a formula for each layer blending, that can be different for each. For the pile of cards, you can say that you want to merge only the red colors in the final rendering, or the pixels that are above a certain saturation value, or below a certain brightness, and ignore all other, or multiply the pixel values. If you have a pile of blue and red cards, and only merge red, you'll end up with a solid big chunk of merge red cards surrounded by bits of untouched blue cards below (assuming the top card is red).
As you pointed out, each of the layers have an opacity value (alpha-blending) which is independent from the blending mode.
It is quite easy to grasp if you can get in touch with a photoshop version : simply create a bunch of layers with different geometrical shapes on them, and play with the predefined blending/compistion mode for each layer.
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In essence:
This function works, but it uses callbacks, and does the alpha blending during the callback's destination call:
static void composition_solid_source_over(const composition_params& params)
{
uint32_t color=params.color;
if(params.const_alpha != 255) color = BYTE_MUL(params.color, params.const_alpha);
uint32_t ialpha = 255 - plutovg_alpha(color);
for(int i = 0; i < params.length; i++) {
uint32_t col;
if(params.canvas->read_callback!=nullptr) {
::gfx::vector_pixel c;
params.canvas->read_callback(::gfx::point16(params.x+i,params.y),&c,params.canvas->callback_state);
col = color + BYTE_MUL(c.native_value, ialpha);
} else {
col = color;
}
if(params.canvas->write_callback!=nullptr) {
params.canvas->write_callback(::gfx::rect16(params.x+i,params.y,params.x+i,params.y),::gfx::vector_pixel(col,true),params.canvas->callback_state);
}
}
}
This one works too, even though it could be more efficient if I updated BYTE_MUL() to handle RGBA instead of ARGB:
static void direct_rgba32_composition_solid_source_over(const composition_params& params)
{
uint32_t* dest = (uint32_t*)(((uint8_t*)params.direct_rgba32) + (params.y * params.stride)) + params.x;
uint32_t color = params.color;
if(params.const_alpha != 255) color = BYTE_MUL(params.color, params.const_alpha);
uint32_t ialpha = 255 - plutovg_alpha(color);
for(int i = 0; i < params.length; i++) {
dest[i] = vector_to_rgba32(color + BYTE_MUL(rgba32_to_vector(dest[i]), ialpha));
}
}
This does not:
static void direct_rgb16_composition_solid_source_over(const composition_params& params)
{
uint16_t* dest = (uint16_t*)(((uint8_t*)params.direct_rgb16) + (params.y * params.stride)) + params.x;
uint32_t color=params.color;
if(params.const_alpha != 255) color = BYTE_MUL(params.color, params.const_alpha);
uint32_t ialpha = 255 - plutovg_alpha(color);
for(int i = 0; i < params.length; i++) {
uint32_t read_col=rgb16_to_vector(dest[i]);
uint32_t col = color + BYTE_MUL(read_col, ialpha);
dest[i]=vector_to_rgb16(col);
}
}
Check out my IoT graphics library here:
https://honeythecodewitch.com/gfx
And my IoT UI/User Experience library here:
https://honeythecodewitch.com/uix
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honey the codewitch wrote: This does not:
Yes, because uint32_t read_col=rgb16_to_vector(dest[i]); probably causes information loss.
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Do not bother with Adobes monster portals. Get GIMP, free, it has the same-ish blend modes, even if naming might vary.
"If we don't change direction, we'll end up where we're going"
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Nah, it is like all these MSOffice clones : good, but does not top the real thing.
Actually, I am still using Photshop 7 - No online licensing required, and just enough features for me to be able to know most of them.
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Thoughts and prayers for our programmer friends from the Sunshine State (Florida), as Hurricane Milton will be making landfall this evening.
![Rose | [Rose]](https://codeproject.freetls.fastly.net/script/Forums/Images/rose.gif)
The difficult we do right away...
...the impossible takes slightly longer.
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We're still recovering from Helene!
Luckily this one is going south of us and will have minimal impact.
A home without books is a body without soul. Marcus Tullius Cicero
PartsBin an Electronics Part Organizer - Release Version 1.4.0 (Many new features) JaxCoder.com
Latest Article: EventAggregator
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Perspective is everything. I know someone in south Tampa and she's freaking out right now. Can't say I blame her.
Did you get through Helene ok? And of course, did all your computers survive?
Jeremy Falcon
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Jeremy Falcon wrote: I know someone in south Tampa and she's freaking out right now. Can't say I blame her.
Ditto, they're fixin to get hit hard, hope she stays safe.
We got though without any damage but we had about 30 trees down. We think the way some are twisted off that we had at least one tornado come through our area. There's a swath through our neighborhood were it is obvious something bad went through by the amount of damage and we are the worst hit. We bought the house because of all the beautiful trees and now there are hardly any left, turns out they were all end-of-life water oaks.
We have 3 acres with a frontage of about 300 yards and we have enough debris stacked along the road to fill an estimated 10 large dump trucks.
Luckily we had family and friends help with cleanup.
Funny while we were cleaning up we had people drive by, slowly gawking and taking pictures.
A home without books is a body without soul. Marcus Tullius Cicero
PartsBin an Electronics Part Organizer - Release Version 1.4.0 (Many new features) JaxCoder.com
Latest Article: EventAggregator
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