how to blend TriMesh with background?

how to blend TriMesh with background?

in Using Cinder • 10 months ago

Hi

I have a TriMesh which is being lit by a point light (thanks paul.houx). The lighting works...

but... there had to be a "but" :)

I want a "sun-like" light source. You can see I am not OpenGL-savvy given the way I phrase the question. I know there must be a term for that which I'm unaware of. If I don't use OpenGL I kind of can do it:

That is a Processing test. It uses a basic directional light. It does not work for me because a) poor performance and b) aesthetic reasons. I moved the project to Cinder and this is what I have now:

This is much more the look I want but I don't want to see the mesh rectangle edges. In the other image you don't see where the terrain starts or ends (it is a slightly different mesh but still). I would like for the mesh to "blend" with the background as in the first capture.

Can this be done?

Thanks

Replies(8)

num3ric

Réf.: how to blend TriMesh with background?

10 months ago

Hey, I've had this problem once and simply made my quads so large that you couldn't differ them from the horizon. Not sure if it's the best way to solve this problem though. In any case, it could also be done here by surrounding the current terrain with 8 huge simple quads. Furthermore, by doing so you would preserve the gray color with the white highlights.

Or maybe you could just add another huge quad at level y=0, but I'm fearing z-fighting issues. Still worth a try, they are both white after all so maybe there are no problems here.

If not, maybe shaders could help to solve this (given that you know how to setup the whole lighting in glsl, i.e. http://www.lighthouse3d.com/tutorials/glsl-tutorial/directional-light-per-pixel/ ).

For example, say your grid has texture coordinates from (0,0) to (1,1) from one corner to the opposite. Then maybe you could add a factor to progressively color the vertices white as you're further from the center using some sort of distance(vec2(0.5, 0.5), texCoord) or distance to the edge, in addition to the lighting.

Still using shaders, another idea may be to max out the white color only on the flat floor (using vertex height and/or the normal which is pointing perfectly up).

Also, what about white fog? It could look awesome. http://nehe.gamedev.net/tutorial/cool_looking_fog/19001/

Éric

P.S. It's too bad we're not doing ray-tracing because infinite planes are so easy to do... intersect the ray with y=0 and you're done.

mauricio...

Re: how to blend TriMesh with background?

10 months ago

Thanks for the many options.

I think the solution gravitates around "max out the white color only on the flat floor (using vertex height and/or the normal which is pointing perfectly up)" because that's what I want. Horizontal areas should be all white (no grays).

Will look into that.

Thanks

mauricio...

Re: how to blend TriMesh with background?

10 months ago

Hi

After reading (and not understanding much of) the Open GL tutorial in Lighthouse 3D, I finally managed to get here:

For the other GLSL n00bs like me who want to know how (and if someone can correct this cause it probably is not very kosher), assuming you already have vertex and fragment shaders:

I needed to know if the vector I was drawing was zero height (my height map assumes anything not to be drawn or unimportant is black). For some reason I couldn't figure that out in the fragment shader (which is the one that draws stuff) so
I added a varying variable in my vertex shader:

varying vec3 myV;

and assigned it to the .xyz value of the vertex inside the main() function:

myV = gl_Vertex.xyz;

I added that same variable in the fragment shader and then verify its y-value before returning the frag color:

// final color
if (myV[1]==0.0) {
gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);
} else {
gl_FragColor = pow(Iamb + Idiff + Ispec, gamma);
}

I return all white in my case. I actually do that check before anything else in the frag shader so as to prevent unnecessary calculations. I still get some greyish tones for surfaces far away from the light source but well... this is already much better.

Thanks

num3ric

Re: how to blend TriMesh with background?

10 months ago

Well, that was fast!

I have another idea now that this is working. The problem you now have is that the transition from white to the normal lighting is very abrupt. It should be smoother.

One way to do so is to replace the if/else statement by an interpolation or transition factor.

I don't know how the height of your mesh varies but say it goes from 0.0 to 5.0. We would like a soft transition from white to normal shading between 0.0 and 0.75.

float lighting_factor = clamp(gl_Vertex.y, 0.0, 0.75) / 0.75;
gl_FragColor = (1.0 - lighting_factor) * vec4(1.0, 1.0, 1.0, 1.0) + lighting_factor * pow(lamb + ldiff + lspec, gamma);

Or even better, use the smoothstep function:

float lighting_factor = smoothstep(0.0, 0.75, gl_Vertex.y);
gl_FragColor = (1.0 - lighting_factor) * vec4(1.0, 1.0, 1.0, 1.0) + lighting_factor * pow(lamb + ldiff + lspec, gamma);

The smoothstep could even be from 0.35 to 0.75 for example, to completely eliminate low planar surfaces.

Éric

mauricio...

Re: how to blend TriMesh with background?

10 months ago

Éric

That's a good idea. Amazing all the things that can be done with shaders. This is the original, no transition, result:

This is using smoothstep between 0 and 1:

This is between 0 and 2:

I guess I'm gonna leave it at 0-2 since it has the best result.

I also made some changes to the depth map removing some extraneous bumps getting this result:

This is looking much better from what I had already. Is there a way for the grey to not be so intense as pixels get away from the light source? I tried increasing the ambient value but that just "washes out" all the color... I need the reds to be very intense.

Thanks

num3ric

Réf.: how to blend TriMesh with background?

10 months ago

First thing to try is to move your light source far away. Why? The diffuse term in the lighting is based on the angle between the surface normal and the light direction vector (dot product). If the light source is far, the light direction vectors will be more parallel and the lighting will be more uniform. Just like the sun :)

Actually, I guess you could pass the light direction vector to the shaders (reminder: using a glsl uniform variable). That way, the vectors would actually be parallel.

Second thing I would try is to play with the gamma correction value in pow(lamb + ldiff + lspec, gamma). Try to lower it a little.

Éric

P.S. Yes, shaders are addictive. And I'm stuck on my old mac with a prehistoric glsl version. I look forward to the day where I will become totally addicted to the more recent versions of glsl/cg.

mauricio...

Re: how to blend TriMesh with background?

10 months ago

I love it when things have a solution much simpler than anticipated. Indeed, I raised the light a bunch and:

The transition factor is now unnecessary also...

Thanks a lot.

hperigo

Re: how to blend TriMesh with background?

10 months ago

pretty cool thing you got there =)

a little tip from an n00b (that´s me), normally 3D programs like Blender have a light distance falloff option, that is, the bigger the distance to the lamp, the darker the shaded area gets. Maybe you can use this "falloff" as a tint factor?

in blender user manual there is a good article about that:

http://wiki.blender.org/index.php/Doc:2.6/Manual/Lighting/Lights/Light_Attenuation

(with some formulas!)

bye

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