Transparency in textures.

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JensAyton
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Post by JensAyton » Wed Apr 04, 2007 5:58 pm

Funny you should say that… While researching shaders, I saw this, and thought, “that’s silly”. Then, a couple of days later, I remembered Your Ad Here, and something went “click”. My version is a bit more complex:

Image
Image
Image
Image

Uses a single 128x256 texture with four adverts in, and crossfades between them. I’ll probably switch to using a texture to define the pixel masks rather than calculating them, though, because it’s a tad slow on my GeForce FX 5200.

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Post by Arexack_Heretic » Wed Apr 04, 2007 11:41 pm

That looks way more complicated than what I envisionaged!

You could probably even simulate TV with that... a very small one.

Not very usefull for displaying the detail on that specific add though.

---

What I had in mind was a simple flip-state shader, that flips through its textures rather in a stepped/discreet sine than the normal sine used in the Freaking Thargoids example.
As static picture, it should work for the YAH!_oxp on a default grey background.
...will probably look better with a fadeOut1-grey-fadeIn2 though
...have to think on possible mathematical tricks to get the pictures to display longer than the blank-screen.

With possible transparency, the dream of putting animated neon signs outside my Hermitage-wateringhole comes one step closer.
As a plus, neon signs are binary, no fuss with fading etc. :D

---

Back to your pixel-display.
...may be more logical for a highrisk, high-entropy environment such as exists near a witchpoint then a singlepiece solidstate viewscreen.

No idea whether you seriously intend to work this out to perfection or whether you are just playing around with the possibilities...

...Is there a possibility to bodge in a few (determined by system richness?) random 'broken' pixels or a triggered 'static' wave?

...Can this display a scrolling text?
Like those 80's LED-boards...

...How efficient is this technique?
For a simple Flasher sign spelling a single word... say BAR,
would it be more efficient to plot and place flashers or will you be able to streamline this script to an extend that it allows G-cards without a shedload RAM to run smoothly?

Code: Select all

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***   *  *  *  *
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Post by JensAyton » Thu Apr 05, 2007 2:27 am

Arexack_Heretic wrote:Not very usefull for displaying the detail on that specific add though.
Yeah. Obviously if you use too high resolution, you don’t see the “pixels”, so it’s pointless. I was expecting to need to go down to 64x32, but 128x64 seems like it will work.
Arexack_Heretic wrote:What I had in mind was a simple flip-state shader, that flips through its textures rather in a stepped/discreet sine than the normal sine used in the Freaking Thargoids example.
So not a sine, then. ;-)
Arexack_Heretic wrote:As static picture, it should work for the YAH!_oxp on a default grey background.
...will probably look better with a fadeOut1-grey-fadeIn2 though
...have to think on possible mathematical tricks to get the pictures to display longer than the blank-screen.
At the moment, I’ve got four different ads. Each is shown for X seconds, then cross-faded to the next over Y seconds. The crossfade could easily be adjusted to a fade in followed by a fade out. Code chunks:

Code: Select all

uniform float       time;

const float         kDisplayTime = 5.0;
const float         kFadeTime = 1.5;
const float         kLoopTime = 4.0 * kDisplayTime; // 4.0 as in the number of frames

/* ... */

float AdvertContribution(in float offset)
{
    float t = mod(time - offset + kFadeTime, kLoopTime);
    
    float rising = kFadeRatio * t;
    float falling = (kFadeRatio * (kDisplayTime + kFadeTime - t));
    return clamp(min(rising, falling), 0.0, 1.0);
}

/* ... */

// Calculates the intensity of a single virtual pixel
vec3 PixelColor(in vec2 virtualPixelCoord)
{
    virtualPixelCoord /= 4;
    
    // Load texture values for each frame
    vec3 frame0Col = texture2D(tex0, virtualPixelCoord).rgb;
    vec3 frame1Col = texture2D(tex0, virtualPixelCoord + vec2(0.0, 0.25)).rgb;
    vec3 frame2Col = texture2D(tex0, virtualPixelCoord + vec2(0.0, 0.50)).rgb;
    vec3 frame3Col = texture2D(tex0, virtualPixelCoord + vec2(0.0, 0.75)).rgb;
    
    /*  Calculate contribution of each texture.
        Animation works as follows: each billboard is shown for kDisplayTime + kFadeTime seconds
        each display cycle. The beginning and end of this time is a crossfade. kDisplayTime can
        be thought of as the time each texture is at >= 50% visibility.
        The animation cycle starts with tex0Contrib just having reached 1.0.
    */
    float frame0Contrib = AdvertContribution(0.0);
    float frame1Contrib = AdvertContribution(kDisplayTime);
    float frame2Contrib = AdvertContribution(2.0 * kDisplayTime);
    float frame3Contrib = AdvertContribution(3.0 * kDisplayTime);
    
    vec3 result;
    result  = frame0Col * frame0Contrib;
    result += frame1Col * frame1Contrib;
    result += frame2Col * frame2Contrib;
    result += frame3Col * frame3Contrib;
    
    return result;
}
Arexack_Heretic wrote:With possible transparency, the dream of putting animated neon signs outside my Hermitage-wateringhole comes one step closer.[/code]
Let me reiterate: transparency may seem to work under some circumstances, but it doesn’t really. You will eventually run into weird artefacts that you can’t fix.
Arexack_Heretic wrote:No idea whether you seriously intend to work this out to perfection or whether you are just playing around with the possibilities...
I intend to finish it off, some time. Being distracted by this delayed 1.68 for several days. Now being distracted by extending JavaScript support is distracting me from this. :-)
Arexack_Heretic wrote:...Is there a possibility to bodge in a few (determined by system richness?) random 'broken' pixels or a triggered 'static' wave?
I added the entity_personality uniform (a per-entity random number) for this precise reason, but implementing a sufficiently random-looking noise function based only on entity_personality and texture co-ordinates turned out to be challenging. Using those factors + a noise texture might do it. (There’s also a family of noise() functions in GLSL, but they’re not implemented on all hardware.) At the very least, entity_personality can be used to allow multiple signs that aren’t in perfect sync.
Arexack_Heretic wrote:...Can this display a scrolling text?
The current one can’t, but adapting it to scroll a texture instead of doing the fading thing would be quite easy.

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Post by Arexack_Heretic » Thu Apr 05, 2007 5:42 am

wow.
you have already put rather some effort into this.
:shock:
I'll think some on the fade out, but obviously your math (and code-skill) is far superior to mine.

-transparency ...
That dome... looks like oolite draws objects the same way elite did, leaving out the occluded vertices and edges/faces.
This great thing for vector grafix could prove to be a problem for transparent structures.
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Post by JensAyton » Thu Apr 05, 2007 12:27 pm

Arexack_Heretic wrote:looks like oolite draws objects the same way elite did, leaving out the occluded vertices and edges/faces.
Yes. It’s called backface culling, and is universally agreed to be the Right Thing for code intended to draw opaque objects. :-)

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Post by Arexack_Heretic » Thu Apr 05, 2007 12:38 pm

lol.
opaque being the key operator here...
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