Drawing textures, but ONLY where current render-target is NOT transperant! [SOLVED]

Graphics
#1

I want to super-impose a texture on top of my tiles.

I need my texture to be drawn only where the current render target is NOT transparent.

the current render target starts out transparent, then gets level geometry drawn, and I want to overlay a texture ONLY where geometry is already drawn, NOT the transparent bits.
-NOTE that level geometry can have any shape, so I need overlay - functionality, or some sort of masking.

-Is there some blend-state setup for this? Or would I need some sort of pixel shader?

#2

Easiest way to do it would probably be using a shader. Check if the alpha channel has any value for each pixel

#3

That won’t work, he is asking to be able to test the destination render target which you can’t do in a shader

You could use a blend function, but I can’t think of one that would work off the top of my head.

Or a stencil test would work

But really why I can’t see why you want to do this

If you are rendering the level geometry , why not pass in the overlay to the same shader and no the level geometry and overlay in a single shader

#4

You should be able to do it with a custom blend state. I think this is what you want:

new BlendState("InvDestAlpha", Blend.InverseDestinationAlpha, Blend.DestinationAlpha);
1 Like
#6

Please, tell me more about this stencil test… Sounds like something I could use.

#7

thanks markus

Hey Thank you! I have tinkered with what you gave me, but I could not achieve results…

I can use blend-states, I just don’t know how to configure this one.

Can you help by being more specific:
What parameters of a new blend-state do I need to set, and to what values?

#8

Oh sorry, the constructor I was using is private. The idea was to set the following parameters:

ColorBlendFunction = BlendFunction.Add;
ColorSourceBlend = Blend.InverseDestinationAlpha;
ColorDestinationBlend = Blend.DestinationAlpha;

That should give you the color output you’re looking for. You can also control the alpha output, there are the same 3 parameters starting with Alpha. I guess you want to leave the alpha values untouched, this should do it:

AlphaBlendFunction = BlendFunction.Add;
AlphaSourceBlend = Blend.Zero;
AlphaDestinationBlend = Blend.One;
1 Like
#9

SO CLOSE :slight_smile: Your values are cool, and I am saving them for something else, BUT they produce the opposite result of what I wanted - They super-impose on everything that IS transparent, while I am looking to super-impose on everything that IS NOT transparent. Can you advise how to get the reverse? I will post if I guess the correct values.

#10

delete
delete1024Ă—459 65.6 KB

It worked, I tweaked the values to following:

ColorBlendFunction = BlendFunction.Add,
ColorSourceBlend = Blend.DestinationAlpha,
ColorDestinationBlend = Blend.DestinationAlpha,
AlphaBlendFunction = BlendFunction.Add,
AlphaSourceBlend = Blend.Zero,
AlphaDestinationBlend = Blend.One,

2 Likes
#11

Hey markus! I have noticed a problem :frowning: So I think the additive color blending means, means that a black overlay will not draw at all, and MOST images will be slightly translucent (darker = more translucent), … I was hoping for a way to superimpose any image, even if it has black on it.

Any thoughts?