Print Page - Mandelbox render glitch

Title: Mandelbox render glitch
Post by: lapinot on September 19, 2015, 03:16:56 AM

Hi,

Im trying to render the Mandelbox with http://blog.hvidtfeldts.net/index.php/2011/11/distance-estimated-3d-fractals-vi-the-mandelbox/ (http://blog.hvidtfeldts.net/index.php/2011/11/distance-estimated-3d-fractals-vi-the-mandelbox/) formula but it seems I don't cut it.

Here's my almost unmodified code (HLSL) (FScale = 2.2) :

Code:

float fixedRadius2 = 1.0 * 1.0;
float minRadius2 = 0.5 * 0.5;
float foldingLimit = 1;

void sphereFold(inout float3 z, inout float dz) {
	float r2 = dot(z,z);
	if (r2 < minRadius2) { 
		// linear inner scaling
		float temp = (fixedRadius2/minRadius2);
		z *= temp;
		dz*= temp;
	}
	else if (r2 < fixedRadius2) { 
		// this is the actual sphere inversion
		float temp =(fixedRadius2/r2);
		z *= temp;
		dz*= temp;
	}
}

void boxFold(inout float3 z, inout float dz) {
	z = clamp(z, -foldingLimit, foldingLimit) * 2.0 - z;
}

float DE(float3 z) {
	
	float3 offset = z * FScale;
	float dr = FScale;
	
	for (int i = 0; i < FMaxIterations; i++) {
		boxFold(z,dr);       // Reflect
		sphereFold(z,dr);    // Sphere Inversion

		z = FScale * z + offset;  // Scale & Translate
		dr = dr * abs(FScale) + 1.0;
	}
	float r = length(z);
	return r / abs(dr);
}

Alternatively I tried with (Buddhi's ?) :

Code:

float3 z = pos * FScale;
	float DEfactor = FScale;
	float fixedRadius = 1.0;
	float fR2 = fixedRadius * fixedRadius;
	float minRadius = 0.5;
	float mR2 = minRadius * minRadius;
	
	for (int i = 0; i != FMaxIterations; i++) {

		if (pos.x > 1.0) pos.x = 2.0 - pos.x;
		else if (pos.x < -1.0) pos.x = -2.0 - pos.x;
		if (pos.y > 1.0) pos.y = 2.0 - pos.y;
		else if (pos.y < -1.0) pos.y = -2.0 - pos.y;
		if (pos.z > 1.0) pos.z = 2.0 - pos.z;
		else if (pos.z < -1.0) pos.z = -2.0 - pos.z;

		float r2 = pos.x * pos.x + pos.y * pos.y + pos.z * pos.z;

		if (r2 < mR2) {
			pos *= fR2 / mR2;
			DEfactor = DEfactor * fR2 / mR2;
		}
		else if (r2 < fR2) {
			pos *= fR2 / r2;
			DEfactor *= fR2 / r2;
		}

		pos = pos * FScale + z;
		DEfactor *= FScale;
	}
	
	return min(2.0, sqrt(pos.x * pos.x + pos.y * pos.y + pos.z * pos.z) / abs(DEfactor));

but no good results either.

Anything obvious ? Thanks for your time.

Title: Re: Mandelbox render glitch
Post by: mclarekin on September 19, 2015, 04:09:25 AM

To confuse you here it is in Buddhi's openCL code
NOTE:-

Initial Conditions outside the loop
Initial DE = 1.0f;
Initial z = point

Inside the loop
DE = DE * fabs( m ) + 1.0f;
and the adding the addition constant multiplier in z = z * m + c ;
c = point * constant multiplier . The constant multiplier is a default of 1.0f for standard Mboxes,
BTW it is more fun setting up the constant multiplier as a vector of so you can tweak z.x, z.y & z.z by individual constant multipliers

BTW z = z * m + c + cj, is even more fun, with cj being a vector3 of simple addition constants (julia)

Hope this helps

Code:

int3 cond1, cond2;

	//Box fold
	cond1 = isgreater(z, foldingLimit);
	cond2 = isless(z, -foldingLimit);
	z = select(z,  foldingValue - z, cond1);
	z = select(z,  -foldingValue - z, cond2);

	//Spherical fold
	float rr = dot(z,z);	
	float m = scale;	
	if (rr < mr2)	m *= native_divide(fr2, mr2);
	else if (rr < fr2)	m *= native_divide(fr2,rr);

	Applying spherical fold (modified m)  and adding the addition constant multiplier
	z =  z * m + c ;

	DE = DE * fabs( m ) +  1.0f;

	r = distance(z, orbitTrap);
			
	colourMin += fabs(m  );			

//Bailout
	if(r>1024.0f)

Title: Re: Mandelbox render glitch
Post by: lapinot on September 19, 2015, 02:21:42 PM

Okay better now. ;D

(http://grid.turtlespeak.net/upload/LMo6pu2bZ3pYC5QU/lMiQKOZTmLoMe9nF/mandelbox-1.png)

Not sure what the culprit was - half my rendering code and not setting init values for DEfactor / z correctly.

Thanks for the help.

-Lap

Welcome to Fractal Forums

Fractal Software => 3D Fractal Generation => Topic started by: lapinot on September 19, 2015, 03:16:56 AM