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# Creating Blood Drops on Screen

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6 replies to this topic

### #1Medo3337  Members

Posted 10 June 2012 - 07:21 PM

I am looking for a way to get blood drops falling on the screen, I can use Sprite to put blood drops on the screen, but not sure how to get the blood drops to fall on the screen.

### #2Washu  Senior Moderators

Posted 10 June 2012 - 07:23 PM

Do you mean something like:

Its raining outside. The camera looks up and raindrops (which you can see falling) land on the lens of the camera and persist there?

If that's the case, you can use some sort of a basic collision detection to determine when a droplet intersects the camera and then project it onto a plane in front of the camera.

Edited by Washu, 10 June 2012 - 07:24 PM.

In time the project grows, the ignorance of its devs it shows, with many a convoluted function, it plunges into deep compunction, the price of failure is high, Washu's mirth is nigh.
ScapeCode - Blog | SlimDX

### #3Medo3337  Members

Posted 10 June 2012 - 08:23 PM

Yes, something similar, I don't need to detect collision, I need to put blood/rain drops on the screen and make them appear like they fall on the screen (the blood/rain drops should be moving down)

### #4jefferytitan  Members

Posted 10 June 2012 - 11:19 PM

I'm guessing that you more want help with fluid simulation (e.g. fluid running down a surface) than the fact that it's the camera. Doing it properly is ridiculously hard and involves serious fluid dynamics equations. Alternately you could do a simple 2D simulation that takes into account the specific features that you want it to. For example, start with "moves downwards" and "conservation of water volume", then add on features until it matches what you want, e.g. "drops merge together", "large drops travel faster".

### #5Washu  Senior Moderators

Posted 11 June 2012 - 01:21 AM

There are actually a couple of ways to fake it, you can try what jefferytitan suggests. Another option would be something similar to contrails or engine trails. That is you have your base "spot of blood" on the camera lens. Then what you do is you apply gravity to that spot, as it travels down the screen what you would do is generate a strip of triangles behind its direction of travel that would be textured with a semi-transparent "blood smear" texture. Think of it like thin red film that the blood spot leaves behind as it travels. You could then use a simple mesh for your blood dots, and animate the mesh to make them appear to change shape. Scaling could be used to make it appear as though they merge as well.

In time the project grows, the ignorance of its devs it shows, with many a convoluted function, it plunges into deep compunction, the price of failure is high, Washu's mirth is nigh.
ScapeCode - Blog | SlimDX

### #6Tom KQT  Members

Posted 11 June 2012 - 01:40 AM

Maybe you could also make an "offline" animation (video) of some falling drops and then blend it with the screen as a post-process? You would have to prepare multiple drops, otherwise they would all be exactly the same.
You even probably could record and use real water drops?

### #7Medo3337  Members

Posted 11 June 2012 - 05:07 AM

I think that will work very well to acheive what I want, however, how can I play animation video on the screen with alpha blending and color keying the black in DirectX during the game rendering?

Edited by Medo3337, 12 June 2012 - 02:46 AM.

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