Something is wrong with colour blending when opacity is involved

d.healey

@tomekslesicki I still don't understand what you're trying to do. Could you provide an image that shows how you want the end result?

tomekslesicki

@d-healey ok, the idea is:

there's a panel that contains some controls: buttons, sliders, whatever
when a button is clicked, I want to make the panel look as though it was semi-transparent

An equivalent of this in any graphics app would be:

there's a background and a group of layers
when a button is pressed, the opacity of the group of layers is changed to 50% or so.

A while ago @Christoph-Hart suggested that if the background is solid (it is), I can achieve the same look by overlying a semi-transparent block of solid colour over the sliders. This is true, because the same look can be achieved like this:

the background has a solid colour
there's a panel put on top of the sliders: the panel has the same colour as the background but opacity of 50%
so if the panel is on top of the sliders, they look as though they were 50%

This is good BUT the problem is that the colours are changing when one of the panels has an opacity other than 1. So if I overlay a panel that has the same colour as the background but an opacity of a value that's not 1, HISE renders it as a different colour, even though it should render as the same colour of the background because in any other graphics app, if you:

have a background of one colour
put a layer of the same colour on top and set it's opacity to 50%
the result is still the same colour - they look as one solid block

Does that make sense now?

Now, the strange this is: if I'll use a .png that looks like one solid block of colour and change the opacity of that, it renders correctly. Hence the bug report.

tomekslesicki

@Christoph-Hart I just tested on Windows and the results are the same so I guess it’s not mac-related after all.

d.healey

@tomekslesicki I'm not seeing a change in colour, I just see the opacity stacking up as you overlay one on top of the other.

HiseSnippet 1127.3ocsW0saaaCElJNJq1qMaEXO.B4JEfLC4jl1ATLTG+2fwZR7h6J1tpfVh1hKxjFRTMwan2rmpc4tcuE6pc8dCxNTT1hxQ1S0aIAHH7vyOe76b3gGMHj6Rhh3gHipuY9LBx3wlCmyD9s8wTFpeGjw9lmiiDjPKknVymgihHdHCiJeiTfQ0cQI+72upEN.ybIYhPn2xotjWSmREYRGz7aoAA8vdj2Pmpo8yZ12kyZyC3w.dpX5flgcuFOgbAVp1NlHi855QE7vgBrfDgL1sE2a9Pe9MLk9ukFQGEPjKZfFBNRItGOvShXoTTaeZf2fEm6HD3kAYrPEEK7ElmS8nKkmwFedxFVYVnyGF6jGdUxAuF5vyQCdE.ICMHsqBRO0bnaHclHaGId9Ty9LH4LFCztNTT5h14OpX1lCZvD0mhulzKDVrzB6m63bjE7mCeYsZ.0GIrdONzpEv5SB4wLOqu1Zg0SHh17oy3LXg8AYpb.XaloWN5mHth0ZlZ6CxGtQK80jPxbvVma6063tvuc.8xhT8HhX.jGDWwiETFwdbLyUP4L6IGV6WpUcR8wPY0YAA148HDsOHinJ3k2KpBwn52PE9mELyGuheOxxo9KN8Pv0UklEIOoRKJkgJ6TA6J.V1BeZjjsdM2EGzRpZj8wNK89l06zxo2Ikzemj3uDRq18RtoEw+K43TsRR00nr.fosVvzVbVNkj9IjGX6tvIGAgKHljjOVj0faQKzSsI.Pv2kBCpbShwswAAxrgcwX3vWpAxK3BxkL6DXT6C0rVcqwiKbuTWEPBKbaYOuvMYnMKd5HRnNIHUDZDju6h456tn27yUwPZJxY8YTwkyHr00RDkRqPmnJonB9OQRen8S6C0JVH3LDEZ27Yl43RTBv0eX.UJmnKpwpNIETE4jgATORXNmnDk2I+428a+0qPee+NXAV1hM8LBm6YjPAURoFcHuGduR0vspYGRz0B9rDRHs1BdfTE7mrncLlQBRh8iMy5UgtUG4y0WbC0S3uTvu+qM8IzI9BcIi3g.5GR+4bmekzqvdz3nbxmr3Iyp6c2c2kHiJHSyjtPyLoGqKVPtUbeWfzNy6U5TeYO2neb0yMHAUFZtlYZcPjdvnMmquXkfQuWvnMWKcVH4WLGsFBsX1un7TtJqOoz2MtUm09XY4Y3PHbZwUiQQqGNa3V1+ojdYgy9qqf3QokfkGFEVN7vbK5i6p7l3BBCCWvRFtCc+oCg4R4dwAXQ9gUkSnmtA7FStIDkSAxhnh45Mp+eaB1xBwmZNfJb8KFi6T.Fg6LODXLct+mX1c7XnVJCf6Z16GdXFxGol.cx4XQHEpcMuHd5Pn7wk.QmAU2x23M1Q1IVs1QtVx.CILujEPU1coa1Pt1HcyFK1DME6Fxem6xKTFOJQBfIVxGUUE95NXs0xmJMMcp6flBejy6bckG+uDFPnXaNdKr4jsvlmsE1b5VXyy2BadwVXyWsQajee4YwB9T00APvftIirXXzUqEv+7UUAAE

Will you be using LAF to draw your controls?

DanH

@d-healey I might have understood this wrong but can’t you simply hide the solid coloured panel and show a 50% opacity panel when you click the button?

Matt_SF

@tomekslesicki this way works :

HiseSnippet 1056.3ocsWstaaaCElxNLq1qWVA5CfP9kCPWfcVW2JJFlquMXrkDi5thseUPKQKyEIRCJpT6Nz+rmr9Tzmi8FjcntXQkHmo3sj.DDd34xG+34b3QSjBGZXnPhrZ7l0KoHq6imtlqVzeAgwQiGfrdH9DRnhJsSD0a8RRXH0EYYU+mzBrZrGJ9m+9G6Q7IbGZtHD5sBlC8WXALUtzIc+Ylu+HhK8Mr.CseV2wNBdeguHBvScbazRhy4DO5oDsZ0vHq8G5xTB4TEQQCQV60S3td5Bw64I5+VVHalOUunCZJ3nDwiD9tZDqkh5uf46NI6bGh.uLImEpmvBOAeByksQdNa7UwaXmagIeXUqH7pW.dcLgWaC3UBjrLfzdIP5w3oNR1RU9NZ77k3wb3xYNAncSnjnKp1mqg6K.M3piBHmSGIgEarn0ya29o1veN7kMaBTenx9BhztGv5dRQD209Gryr1ip5KBVJ3vhVGjqxAfs4ld1r+f5n1pYIaePwvMaiu7jz0fssWMZzwCgeG.5kGoiBopIv8f50hHEiSaMOh6nXBdKuCa9mMa3czbHs5U99sJ5QHZeTGwjfWcuzd0KdQBLx7PyqcRSuQ+WNvoZEetax39PXsyBqsfWPIsejB+VNYN4oP37inwfK6H.oTY5krI.Pv2UBCZBH039DeeMW0pbLb3KM.4oBE8LdqXXz7iMsu5VymW5dotxmJKcacC.4MYXKdTvLpzjDzJBUEEK0vauTyrSfSBCYnnfOlyTmsjx2V+ATJsBkk0SQE7ep3hxGlVT1KRoDbDCp8dDt.WhhAtYKQTkbhonN2BmL0m4RkEbRhnxbxuNd.QQz8aROiv4dIUpXZJ0Z.8Bn4cR2mF3AzvyUhkwjPZtE7ZQRvePVuIBm5GG66iyKbQqLC5ZyEum4pVrQvm9qtKnLuEJSIyDR.8SYen.zSj9ZhKKJrfbur2OZr+kWdYrLlhFjKMSyboGaJVQWottKPFm48q7UeUO2ne+pmaPBpJzbSbZdPnYvXcWat3JAicsfw5tU5rTxubNZKDZ4reY2SExr9hJWarxj0tsr7RhDBmQbMXTz1gyMTk8e5Rupv4QaKg3doofUGFklNb2TEc6JkuItfxIPAV7jNWj0o2pN55SMAyqIbi7IphCwombMcC34lBSNomNhGxTqMmr8+sI6pJDeLdBS4rnbLVqDLBkO2EXLcd3GfGNeNjVkCv8vi9s6lgeQISl4cBQIYPZL9znfoPljCEhNGRz0O2aUS2TNYca8ZMCLkxciW.IbWltYG8ZqzM6jsIJf3HEuyYSsk08hk.XhG+wFMfu5AVau4USLt8QsQAvv+uywQe7+ZXVgxs43cvluYGr4Y6fMe6NXyy2Aa9tcvlu+FsQ+cWuJRIBRJG.ASFFO8hk0v7tAn+AvMm79H

Just change the hex alpha value of the backgroundgrey "manually"

d.healey

@Matt_SF I don't see a difference.

@tomekslesicki's is on the left, yours is on the right

Matt_SF

@d-healey ah, that's odd... here's what I get

tomekslesicki

Thanks guys, I'm getting the same problem with Matt's snippet, unfortunately.

@d-healey maybe you're right about the opacity stack, but then if 1 is 100%, isn't it a bug that if a semi-transparent layer is overlayed on top of a layer that already is fully visible, the opacity can go above 100%?

d.healey

@tomekslesicki Yes it does seem a little strange

Christoph Hart

Alright, either my monitor is not calibrated correctly or I'm getting blind, but I don't see any difference and this entire topic looks like a big prank to me :)

Can somebody make a clear example that shows the difference like night and day type (and not a colour that is 0xFF292929 but should be 0xFF292928.

tomekslesicki

@Christoph-Hart it's not about night and day, it's just that if it's about creating an impression of a half-opaque panel with controls, it doesn't look good if there's suddenly a rectangle overlaid on top of the panel.

Christoph Hart

@tomekslesicki But where is the rectangle? I don't see a rectangle.

d.healey

@Christoph-Hart

But where is the rectangle? I don't see a rectangle.

Must be a monitor (or eyeball) setting issue :p the rectangle is subtle. I'll see if I can make a clearer example.

d.healey

This post is deleted!

d.healey

Ok here's something interesting.

Alpha values

0.1 = No rectangle
0.2 = No rectangle
0.3 = Rectangle
0.4 = No rectangle
0.5 = Rectangle
0.6 = No rectangle @tomekslesicki Maybe just use this value
0.7 = Rectangle
0.8 = No rectangle
0.9 = Rectangle

Here I have taken the same snippet as before and adjusted the contrast in an image editor

tomekslesicki

@d-healey thanks, David, you're way better at explaining things than I am!

Christoph Hart

@tomekslesicki Ah finally - actually I think that the PNG compression of the screenshot makes the differences even more subtle, but now I have finally proof that you aren't executing an elaborated prank :)

Alright, the minimal use case to demonstrate this issue is:

const var Background = Content.getComponent("Background");

const var backgroundgrey = 0xFF333333;

Background.setPaintRoutine(function(g)
{
	g.fillAll(backgroundgrey);
	g.setColour(Colours.withAlpha(backgroundgrey, 0.6));
	g.fillRect(this.getLocalBounds(50));
});

I've deliberately used a pure grey in order to rule out rounding errors. For me, 0.6 creates the most visible rectangle. Curiously, in a raw JUCE component, it doesn't show that rectangle, so I'll try to check where the error comes from.

Christoph Hart

Curiously, in a raw JUCE component, it doesn't show that rectangle

Nope, my weak eyes struck again, it's actually the same when using raw JUCE.

auto grey = Colour(0xFF333333);

g.fillAll(grey);
g.setColour(grey.withAlpha(0.6f));
g.fillRect(getLocalBounds().reduced(50));

Also shows up that box. Now it gets complicated :)

Christoph Hart

I've posted it in the JUCE forum, let's see how it goes.

Subtle colour error

Hi everybody, it seems that the graphics renderer behaves a bit weird when drawing the same colour over itself with a different alpha value. The best way to reproduce this is this example code: auto grey = Colour(0xFF3…

JUCE (forum.juce.com)

I wouldn't hold my breath that there is an easy solution for this though...

Something is wrong with colour blending when opacity is involved

Subtle colour error

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