POM material

[RyanB]

I was able to save 10 instructions from the main loop by removing the need for the ‘lastoffset’ variable, and also by Multiplying ‘stepsize’ by ‘UVDist’ outside of the custom node (which is plugged into UVDist, stepsize is also still needed for the z offset).

It may be possible to save a few more by simplifying how the ‘yintersect’ variable is passed. That variable is only needed for PixelDepthOffset (without it, the pixel depth offset has harsh step seams) but so far I cannot figure out another way to simplify that without adding an unwanted branch to the function. Any more inputs and it becomes dauntingly unsuable IMO.

Updated code for parallax only node:

float rayheight=1;
float oldray=1;
float2 offset=0;
float oldtex=1;
float texatray;
float yintersect;
int i;

while (i<MaxSteps+1)
{
	texatray=(HeightMapChannel, Tex.SampleGrad(TexSampler,UV+offset,InDDX,InDDY));

	if (rayheight < texatray)
	{
		float xintersect = (oldray-oldtex)+(texatray-rayheight);
		xintersect=(texatray-rayheight)/xintersect;
		yintersect=(oldray*(xintersect))+(rayheight*(1-xintersect));
		offset-=((xintersect)*UVDist);
		break;
	}

	oldray=rayheight;
	rayheight-=stepsize;
	offset+=UVDist;
	oldtex=texatray;

	
i++;
}

float3 output;
output.xy=offset;
output.z=yintersect;
return output;

Also it would be nice to get working for the rayheight<=texatray case since that will be a whole step faster for all white heightmap pixels.
So far when I try to get that working, its causing the first layer either to get invalid results (it attempts to divide by 0) or it doesn’t get the offset to match up with the next layer if I use an offset to keep it from dividing by 0. If anybody can help figure that out that would be awesome and make another tiny bit faster.
A separate if statement works but the branching overhead is probably not worth it unless there are a significant amount of white pixels.

[ZacD]

If you don’t want another input branch, why don’t you just make 2 versions of POM, POM and POM+ or something?

[RyanB]

Not a bad option to consider, but that itself has some downsides since it may not be possible to switch between functions and have all the pins stay connected.
As a test I commented out the yintersect line and returned 0 for that variable and it made no difference to the instruction count. Not that everything you do is properly counted but it may not be enough savings to warrant a separate node.

With Just parallax (no PDO or shadows), it’s showing as 174 instructions right now (with static lighting).

Using PDO the automated way kicks it up to 226 which is crazy (remember that requires 4 texture lookups: ddx-uv, ddy-uv, ddx-world, ddy-world). If you specify the UV-world size manually that brings the PDO cost down to 211. It still seems like a lot. Maybe it is not able to reuse much of the work for the pixel depth offset…

[ZacD]

It’d be cool if UE4’s material editor had a option to swap nodes but keep inputs (wouldn’t it be nice to be able to swap multiply for add or subtract), might want to throw that on a wish list.

[RyanB]

I believe there is already a request ticket for that.

I am trying to test out a blend between a POM material and a regular material. For example if you had bricks or stones and wanted them covered up by moss or mud.
The basic idea is working: use mask * height, and use the difference between that and the WPO.Z value to make a gradient which can be used to create a slope between the two surfaces:

The problem is mapping the 2nd texture. Right now I am using “Virtual Plane Coordinates” with the gradient Z offset from WorldPosition.Z. looks right from the sides, but from opposing views it causes a mirroring effect since the pixels are actually trying to project out to where each would have mapped to their respective planes:

I am guessing there is some kind of solution with line intersection once again but it doesn’t seem obvious how to solve it yet.

Remember line intersection problems can be solved by converting lines into y=mx+b (where m is slope and b is the y value when x=0) or x=y(t)+y(1-t) and making one of the variables equal for both lines. Just need to figure out how to inject the intersection into the virtual plane coordinates math (or probably better replace it with something simpler for ).

[Quark]

Gorgeous work.
So is gonna be included in a future update as an official and permanent solution?

[anonymous_user_bcf66e2c]

@Quark;303375

Gorgeous work.
So is gonna be included in a future update as an official and permanent solution?

Its already in the branch and will be in 4.9. I just cherry picked the commit and am using it now in 4.8 preview 3 and it works well.

[RyanB]

The function was actually saved with a fairly old engine version from around January. It’s still technically a 4.8 build but one of the earliest ones made so anybody on a 4.8 preview should be able to try it out.

[wes_h]

Nice stuff ! Curious, would decals added over geometry take advantage of the pixel depth offset, or would they betray the illusion by rendering flat and intersecting the POM material’s depth?

[RyanB]

Pixel depth offset works fine with decals.
Not the prettiest example (the default decal mat) but you can tell its projecting on the depth since I made the Z scale very shallow and rotated the decal:

[wes_h]

That, is awesome.

[anonymous_user_c94f194d]

float rayheight = 254/255;
Would solve full white first iteration problem?

[Bladerskb]

awesome work

[RyanB]

It does save one step for white pixels (You have to enter it as rayheight = (float)254/255; or alternatively 0.996)

but for some reason it also seems to cause the results from that first step to be offset 1 step backwards instead of receiving 0 offset. It does seem very close to working though, great suggestion.

[RyanB]

Ok I figured it out. It does add 2 instructions to the material but it is hard to say if that cost is meaningful, or if the white-optimization will end up being very important in actual usage.

The top two lines need to say:

float rayheight=0.996;
float oldray=0.996+stepsize;

Adding stepsize to oldray allows the intersection to handle slope the same as the future steps (it simulates a step already having been taken).

Another option to optimize a POM that requires tons of steps would be to generate a distance field from the initial pixels and use that as the first step distance. The cost of the extra lookup and math would probably be a wash unless you were doing lots of steps.

[Sotalo]

, you are a God amongst men. A GOD!!!

As for optimizing the steps, I will reiterate that I tried every possible method to limit the step size from using pixel depth to diminish steps in the distance to a combination of distance and tangents, and nothing gave me a better overall framerate than just a basic tangent calculation: product of camera vector and vertex normal. Unless you need more than 50-60 steps and running a mesh with more polygons than pixels (in which case, holy cow, just model it out or tessellate), any other method to limit steps was rendered moot by the additional instructions.

[anonymous_user_7ef7f636]

I must say that is looking REALLY good!

[Sitrec]

Fantastic work !

[Hevedy]

What is the performance difference between with PDO and the tessellation ?

[RyanB]

I Hevedy,

Good question! We just actually started making a testmap to put into our QAgame project so we can get a better idea.

So far it has various levels of POM on terrain etc but the next step is to make the same comparison with tessellation, attempting to make a few versions that look visually comparable to see how they perform against eachother. With 4.8 coming out soon some things are a bit hectic around here so I am not exactly sure when we will have any findings to share.

That said, I would expect POM to perform very well against tessellation, especially on terrain where tessellation is very slow. A lot of it will depend on a per-asset basis such as the noise frequency of the heightmap etc. There could be cases where one or the other are preferable. Ie a very low resolution lumpy form may look ok with low tessellation levels whereas something super noisy may require more POM steps to look good.

At a certain point using real geometry also wins its mostly for cases where it would be prohibitively difficult to make all those meshes (ie, tiling castle textures everywhere).