[2016.10] Sprite:setBlendMode(src, dst)

n1cke · November 2016

In Gideros 2016.10 `setBlendMode` has extended version with 2 parameters (blend functions): `src` and `dst`. They define how top sprite colors (`src`) will be blended with bottom sprite colors (`dst`). If you are familiar with image editors like Gimp or Photoshop you know they have many ready blend modes to mix layers in various ways for great effects. Those blend modes are just combinations of aforementioned blend functions so we have added direct support of those functions to Gideros.
There are 11 of them: Sprite.ZERO, Sprite.ONE, Sprite.SRC_COLOR, Sprite.ONE_MINUS_SRC_COLOR, Sprite.DST_COLOR, Sprite.ONE_MINUS_DST_COLOR, Sprite.SRC_ALPHA, Sprite.ONE_MINUS_SRC_ALPHA, Sprite.DST_ALPHA, Sprite.ONE_MINUS_DST_ALPHA, Sprite.SRC_ALPHA_SATURATE. This constants are represented in Lua as integers from 1 to 11. Therefore in Gideros we have 11 * 11 = 121 way to mix colors

To test extended `setBlendMode` you can use following snippet:

local topTex = Texture.new("top.png",true)
local btmTex = Texture.new("btm.png",true)
 
lh @ 10 -- label height
 
local w = (application:getDeviceWidth() - lh) / 11
local h = (application:getDeviceHeight() - lh) / 11
local s = math.min(w, h)
 
for x = 1, 11 do
	for y = 1, 11 do
		local top = Pixel.new(topTex, s, s)
		local btm = Pixel.new(btmTex, s, s)
		stage:addChild(btm)
		btm:addChild(top)
		btm:setBlendMode(x, y)
		btm:setPosition(lh + s * (x-1), lh + s * (y-1))
	end
end
 
local t = {}
for k,v in pairs(Sprite) do
	if tonumber(v) == v then t[v] = k end
end
 
for n = 1, 11 do
	local label = TextField.new(nil, t[n], "|")
	label:setX(lh + (n-1) * s + 2)
	label:setY(1)
	label:setClip(0, 0, s - 2, lh)
	stage:addChild(label)
	local line = Pixel.new(0x666666, 1, 1, lh + 11*s)
	line:setX(lh + n * s)
	stage:addChild(line)
end
 
for n = 1, 11 do
	local label = TextField.new(nil, t[n], "|")
	label:setY(lh + (n-0) * s - 2)
	label:setX(1)
	label:setRotation(-90)
	label:setClip(0, 0, s - 2, lh)
	stage:addChild(label)
	local line = Pixel.new(0x666666, 1, lh + 11*s, 1)
	line:setY(lh + n * s)
	stage:addChild(line)
end

Source images and screenshot are attached below but I suggest you to also experiment with other images to better understand how blend functions work.

totebo · November 2016

AWESOME!

Greywine · November 2016

Hi. I'm trying to understand your example. It uses a lot of the newer features of Giderosmobile so it's really cool, but at the same time, slightly confusing for me.

I can grasp the @ macro, Pixel and setBlendMode. What I don't get is the little bit in the middle.

for k,v in pairs(Sprite) do
if tonumber(v) == v then t[v] = k end
end

I don't think I've ever seen someone iterate over Sprite before. What exactly are you doing (besides generating the 11-item table)? Can you iterate over other classes/objects? Why does it show the BlendModes when you do this?

Thanks in advance.

John

n1cke · November 2016

@Greywine: I am just building reverse table: a table where keys are swapped with values.
Since I know Sprite contains numeric constants (1 to 11) only for blend functions I can iterate over Sprite class and when value is a number I am adding it to reverse table: that number becomes a key and that Sprite key becomes a value. In the end I have following table:
t = {
[1] = "ZERO",
[2] = "ONE",
[3] = "SRC_COLOR"
.....
}
And I use that strings as labels on the top and on the left side of the example app.
In Gideros each Sprite class and subclass is represented as a Lua table. Try to iterate over some class with `for k,v in pairs(some_class) do print(k,v) end` and you will see it's methods, constants, etc. That's why we can easily create new subclasses: we are using usual Lua tables and we can store anything we want in them.

Greywine · November 2016

Iterating over classes: good stuff!

I just wasn't sure why the Sprite class returns the blend constants, but once you know, it's definitely an elegant way to display everything.

Great example and thanks for the explanation.

Xman · November 2016

isn't the current setBlendMode function the combination of original setBlendMode and setBlendFunc?

At the beginning, only setBlendFunc is available, setBlendMode is just a simplified function for setBlendFunc most use case.

If we need more blend modes, it's better to just make the setBlendFunc available for advanced users, and keep the setBlendMode simple .

atilim discussed the idea here
http://giderosmobile.com/forum/discussion/406/setblendfunc-help-/p1

n1cke · November 2016

@Xman: `setBlendMode` is overloaded method: one argument to set blend modes as before, two arguments to set blend functions.
Do you mean it's better to create`setBlendFunc` method for this and avoid overloading?

Xman · November 2016

Exactly!
setBlendFunc was set to nil after setBlendMode is created.
It can be made available easily.

n1cke · November 2016

@Xman: see this commit:
https://github.com/gideros/gideros/commit/0bfc155d7f1cb30598f4c9c4a7c6e71bf9bc2c33
As you can see I have refactored Gideros blending source to make it much more clean and simple, without the need of extra utils like `bin2c` and lua-files. Also in this particular case overloading makes sense because setBlendMode(src, dst) still means you set blend mode, only composed from 2 blend functions. Compare it for example with overloaded `Sprite:setScale` where you can use both simplified 1-arg and more complex 2-arg versions.

Xman · November 2016

sprite.lua is not only a "complicated way" for the blending function, we can easily extends the api for Sprite without polluting the C++ code. It should not be deleted.
The creator of the engine atilim won't do such a lot of work to just add a setBlendMode function instead of make the binder code complicated like this.

n1cke · November 2016

C++ code was not polluted because Lua C API is natural way for Lua to interact with lower level languages like C/C++

It is easy to write, it is loaded faster and it doesnt need external convertors to load Lua scripts. And 99% of Gideros source uses Lua C API so it is bin2c-scripts are polluting C++ code, not Lua C API

Xman · November 2016

You may ask @atilim why some Lua functions are implemented in this way.
I think @atilim won't make this modification according to the this thread:
http://giderosmobile.com/forum/discussion/406/setblendfunc-help-/p1
setBlendMode accept two parameters for blendfunc really NOT make sense.

I think you can make the setBlendFunc be available in any way as you like, but just leave anything else as it was.

n1cke · November 2016

Apollo14 · August 2018

Hi guys!
I'm trying to understand Blend Modes.
How to choose blendmode{5,8}? (I've marked it on attached picture)
I've tried

local top = Bitmap.new(Texture.new("top.png",true))
local btm = Bitmap.new(Texture.new("btm.png",true))
stage:addChild(btm)
stage:addChild(top)
 
btm:setBlendMode(5,8)

It doesn't give expected result.

Btw, I've iterated through Sprite class, like in @n1cke 's first post:

for k,v in pairs(Sprite) do
	if tonumber(v) == v then print(k) end
end

I'm getting not 11, but 27 values (new values are STENCIL-related)
Did these values break blendmode order of numbers?

STENCIL_GEQUAL
SRC_ALPHA_SATURATE
DST_COLOR
SRC_ALPHA
STENCIL_EQUAL
STENCIL_ZERO
STENCIL_REPLACE
STENCIL_NOTEQUAL
STENCIL_LESS
STENCIL_NEVER
STENCIL_LEQUAL
STENCIL_INVERT
STENCIL_INCR_WRAP
SRC_COLOR
STENCIL_INCR
ONE_MINUS_DST_ALPHA
STENCIL_DECR_WRAP
STENCIL_DECR
ONE_MINUS_SRC_ALPHA
ONE_MINUS_DST_COLOR
ONE
ZERO
STENCIL_DISABLE
DST_ALPHA
ONE_MINUS_SRC_COLOR
STENCIL_ALWAYS
STENCIL_KEEP

keszegh · March 2020

With default blending, putting a red thing with ~50% opacity on blue background gives me a color which is darker than any of the original colors. I'd prefer it to have an effect of the red dissolving on the blue. Is there a blending mode that can achieve that? (i'm sad and surprised that this is not how it behaves with the standard blending mode)

see the attached image what happens now, the middle of the curve is 100% opacity and it is fading out gradually towards its ends. i hope you understand the effect i want to achieve instead of how it looks now.

you can also notice that there is a boundary of the curve which tries to emulate anti-alias and that's also darker than both the curve's red color and the background's blue color, which is not the desired outcome.

EDIT: i've checked and e.g. in Krita if i paint with this red on this blue then it also gives dark blue boundary instead of proper anti-aliasing, strange. yet i hope there is some combination of blend modes that gives what i'd like to achieve.

keszegh · March 2020

i don't believe that none of you have any ideas how to improve the blending on my figure, please help. (or should i make a separate topic for this?) thanks

MoKaLux · March 2020

keszegh said:
EDIT: i've checked and e.g. in Krita if i paint with this red on this blue then it also gives dark blue boundary instead of proper anti-aliasing, strange. yet i hope there is some combination of blend modes that gives what i'd like to achieve.

If krita does it this way then I think you are stuck!?

rrraptor · March 2020

@keszegh I did a quick test:

stage:addChild(Pixel.new(0x0000ff,1,128,128))
stage:addChild(Pixel.new(0xff0000,0.5,128,64))
local rt = RenderTarget.new(128,128,false)
rt:draw(stage)
rt:save("|D|test.png")

The result color is (127,0,128) in 255 RGB format which is correct. So, maybe the problem is that it seems to you that the color is wrong?)

hgy29 · March 2020

@keszegh, I tried to reproduce your issue with a simple code:

local bg=Pixel.new(0xB0FF,1,300,100)
stage:addChild(bg)
local steps=20
local stsz=300/steps
for k=1,steps do
	local s=Pixel.new(0xFF4000,1,stsz,100)
	stage:addChild(s) s:setX((k-1)*stsz)
	s:setAlpha((steps+1-k)/steps)
end

But it doesn't give the same results as you:

keszegh · March 2020

@hgy29 , i'm not sure it's not the same result, the middle seems to be 'darker' in your case too.
i use meshes though, so there may be a difference with a very low chance. i will try to make an example with both pixels and meshes.
the issue is that i don't really know which would be the 'right' color halfway, but in any case something that does not give an antialias outline which feels darker, whatever this implies.

keszegh · March 2020

i've tried both pixels and meshes with the colors from my above example, it has the same result:

i think the issue is that while this gradient is 'correct', it has darker colors in the middle than in the two endpoints. i've found some texts that seem to be somewhat related to this (perceived) brightness issue:
https://medium.com/the-mvp/finally-a-definitive-way-to-make-gradients-beautiful-6b27af88f5f
https://graphicdesign.stackexchange.com/questions/6246/if-these-colors-all-have-the-same-lightness-then-why-does-my-brain-tell-me-some
but i did not find any solution to the issue using blend modes. neither do i know which would be a 'visually right' 'middle' color.

rrraptor · March 2020

@keszegh probably what you are looking for is this:
https://blog.johnnovak.net/2016/09/21/what-every-coder-should-know-about-gamma/#gradients

keszegh · March 2020

@rrraptor , many thanks, that's it, explained clearly. now browsing through it quickly the only thing i doubt is that there is a non-resource heavy solution (i.e. using blending or something like this) to create antialias border with gamma correction.

rrraptor · March 2020

@keszegh

keszegh said:
create antialias border

apply shader?
Made an example: https://github.com/MultiPain/Gideros_examples/tree/master/FXAA_shader

keszegh · March 2020

thanks @rrraptor, i will try these shaders, as i'm anyhow not happy that i need 3x as many meshes for smooth borders, although it's not clear which is more taxing on hardware, an aa shader or +20000 meshes.

another issue with the shader solution is that in my initial image you can see that strokes can fade out towards their end in my animation app, here also the non-correct gamma issue is apparent, and that won't be solved by an aa shader.

it would be nice to be able to set what color mixing scheme (what is gamma) is used by the app, but i don't know if opengl can do something like this.

ps: i am happy to be on this forum, lot's of knowledge here.

rrraptor · March 2020

Also, added gamma correction shader:
https://github.com/MultiPain/Gideros_examples/tree/master/GammaCorrection
Its super simple

Hm, the problem is that you cant apply shader to a Mesh :P

keszegh · March 2020

@rrraptor , thanks for the gamma correction code as well, it helps to understand this. but in my case i cannot use it as i can't know from the final image (overlays of meshes) if a color of a pixel is intentionally dark or it is an overlay of two meshes with <100% opacity and so needs to be corrected.

keszegh · March 2020

finally having read the enlightening article recommended by @rrraptor and looking for a solution i've found this article: https://learnopengl.com/Advanced-Lighting/Gamma-Correction
so wouldn't this little change help?:
glEnable(GL_FRAMEBUFFER_SRGB);
can you test it somehow, @hgy29 ?
thanks guys

keszegh · March 2020

basically what we need is that every sprite etc is converted to linear space from srgb, then compositing should be done in linear space and at the end only the final composite should be converted back to srgb before sending it to the screen. that would give gamma-correct results.
for reference i attach a gradient between the two above colors which i think is the 'correct' one.

keszegh · March 2020

as a sidenote i vaguely remember that there was a way to change the default shader (the one which all sprites etc.s use). can you tell me if there is such a thing?

hgy29 · March 2020

keszegh said:
finally having read the enlightening article recommended by @rrraptor and looking for a solution i've found this article: https://learnopengl.com/Advanced-Lighting/Gamma-Correction
so wouldn't this little change help?:
glEnable(GL_FRAMEBUFFER_SRGB);
can you test it somehow, @hgy29 ?
thanks guys

Tried, but no effect on my PC.

For the Sprite's default shader: there is not one default shader but severals, nine I think. Gideros selects the appropriate shader depending n the sprite type and settings, but you can override the shader to use with a custom one on a sprite by sprite basis.

Howdy, Stranger!

Categories

In this Discussion

Top Posters

[2016.10] Sprite:setBlendMode(src, dst)

Comments

Howdy, Stranger!

Quick Links

Categories

In this Discussion

Top Posters

[2016.10] Sprite:setBlendMode(src, dst)

Comments