Hi everyone! I am trying to render textured quads in a 3D scene to draw some texts. The bitmaps I’m using behaves as alpha maps, with A=0 for the backgound, A=1 for the glyphs and in-between values at the boundaries between the glyphs and the background. Since those texts are actually part of the…

[image] leoner: I am trying to render textured quads in a 3D scene to draw some texts. The bitmaps I’m using behaves as alpha maps, … The problem is that I don’t know how to blend the semitransparent pixels of the textured quads with the rest of the scene: setting an alpha treshold such that …

Thanks @Dark_Photon , I’m afraid I didn’t provide a clear explanation of the problem, which is not (I think) related to blended color computation itself: The problem is that I need to draw those texts “inside the scene” and since they are fully opaque I need to draw them with depth testing and writ…

[image] leoner: They are fully-opaque except for some portions Then they’re not “fully-opaque,” are they? An object either is opaque or it isn’t. If it’s only partially opaque, then it’s not opaque. You have to do blending if you want this to work.

You are right, however I don’t know how to do that. I can’t disable depth writing and draw my texts with blending (also, they are arbitrarily oriented so a simple back to front sorting wouldn’t work), and I also can’t keep writing and testing depth while drawing them (see example above, the text, b…

[image] leoner: they are arbitrarily oriented so a simple back to front sorting wouldn’t work It’s text; you can figure out a back-to-front order of the quads. It’s not trivial, but so long as they don’t intersect, you can do it. And unless overlapping, transformed text is super-important to…

[image] Alfonse_Reinheart: It’s text; you can figure out a back-to-front order of the quads. It’s not trivial, but so long as they don’t intersect, you can do it. Thanks, I guess sorting is another option to solve my problem. [image] Alfonse_Reinheart: I don’t see why not. Draw all opaqu…

[image] leoner: But texts are not transparent in this case, they have fully-opaque sections and semitransparent ones That’s what “being transparent” is. You cannot treat an object as partially opaque. It either is opaque in its entirety or it must be treated as transparent. [image] leoner…

[image] Alfonse_Reinheart: [image] leoner: (assuming no view direction sorting) Yes, you will get bad results if you start with bad assumptions. Transparency requires sorting. Well, there are order-independent transparency techniques, but they’re really not worthwhile for drawing a bunch…

I know this usually is a problem when no sorting is done when the text is 3D and inside the scene insted of in the GUI. So what you are experiencing is sometimes the text objects blend fine with the background but in some angles they don’t, correct? If so, then it is definitely a sorting issue, you…

[image] Dark_Photon: leoner, you can try Alpha-to-Coverage for this Thanks for the suggestion, I’ll consider it. [image] Dark_Photon: And for that you need sorting. I understand, however, since I could also have transparent 3D objects (just to say “not quads”) in the same scene along …

Semi-transparent cutouts

OpenGL OpenGL: Basic Coding

Dark_Photon May 12, 2022, 11:05am 2

Use Premultiplied Alpha.

Links:

Premultiplied alpha (Tom Forsyth)
Pre-multiplied alpha part 2 (Forsyth)
What is Premultiplied Alpha? A Primer for Artists (David Hart)

A few past forum threads where folks have hit this before:

Text Rendering Problem with Distance Field in WebGL
Textures with alpha and linear mapping