legend for transparent patch object is opaque ?

6 vues (au cours des 30 derniers jours)
Matilda
Matilda le 20 Juin 2018
Commenté : Matilda le 25 Juin 2018
Hello,
I create a simple figure with 2 patch objects where one of the patch is opaque and the other one is transparent (with facealpha set to 0.1) :
figure
x = [0 1 1 0];
y = [0 0 1 1];
patch(x,y,'red')
x2 = [3 6 6 3];
y2 = [3 3 6 6];
patch(x2,y2,'green','facealpha',0.1)
legend('red opaque -> OK','green is opaque instead of transparent -> WHY ?')
The legend does not reflect the fact that the green patch is transparent. I really need my legend to show if the patch is transparent or opaque. Is there a work around ?
Thanks !

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Ameer Hamza
Ameer Hamza le 23 Juin 2018
The problem is actually caused by the Rendrer of the figure object. In R2018a opengl seems to make the legend entries transparent, but in prior versions, you need to switch to 'painters' renderer to get this behavior. For example, try the following
f = figure;
f.Renderer = 'painters';
x = [0 1 1 0];
y = [0 0 1 1];
patch(x,y,'red')
x2 = [3 6 6 3];
y2 = [3 3 6 6];
patch(x2,y2,'green','facealpha',0.1)
legend({'red opaque -> OK','green is opaque instead of transparent -> WHY ?'}, 'Box', 'off')
  2 commentaires
Walter Roberson
Walter Roberson le 23 Juin 2018
Traditionally only opengl supported transparency, but R2014b added transparency for painters
Matilda
Matilda le 25 Juin 2018
Yes this works !
Thanks !

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Plus de réponses (1)

Yun Guo
Yun Guo le 22 Juin 2018
It is not very clear if you want green patch to be transparent, legend to be transparent, or both.
'facealpha' does work as expected. See example below.
  1. I changed the green patch's size so it overlaps with red patch to show transpareny works.
  2. I also removed legend box, so legend looks transparent.
figure
x = [0 1 1 0];
y = [0 0 1 1];
patch(x,y,'red');
x2 = [0.5 2 2 0.5];
y2 = [0.5 0.5 2 2];
patch(x2,y2,'green','facealpha',0.3)
l = legend('red opaque -> OK','green is opaque instead of transparent -> WHY ?');
set(l, 'Box', 'off')
  5 commentaires
Ameer Hamza
Ameer Hamza le 22 Juin 2018
I am trying on R2018a. Since you have R2017b, which I cannot try at the moment. But to correctly check the opacity move the legend over the red portion like this
Matilda
Matilda le 22 Juin 2018
Yes, I had already done that and it's definitely opaque (The forum won't let me insert an image anymore, says I am limited to 10 daily uploads, although how I reached that limit, I am not sure ....).
Anyways, it's definitely 100% opaque. I have both R2017b and R2015a installed on my computer and I get the same problem on both. This is so weird ... I think one of the default setting might have been changed or something similar. I might try to reinstall matlab, see what happens.
If you know of any setting that might cause this behavior, let me know! Thanks !
Mathilde

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