Fixing a ShaderToy shader (lens distortion).

[MarioMey]

I like this shader: https://www.shadertoy.com/view/3tXczj#. It creates like a distorted and misterious magic ball. Like this:

I converted to use it in obs-shaderfilter-plus. I get to this:

#define DARK_EDGES

float4 render(vec2 uv )
{
   	vec2 disorsion = uv - 0.5;
	float aspect = builtin_uv_size.x/builtin_uv_size.y;
	
	disorsion.x *= aspect; // aspect correction
	
	// take distance from center
   	float len = length(disorsion);
	
	// these are the lens parameters
	float k1 = 1.2;
	float k2 = 1.0;
	float k3 = -3.2;
	
	disorsion 
		= disorsion*k1
		+ disorsion*len*k2 
		+ disorsion*len*len*k3;
		// higher powers may be added if necessary
   
	disorsion.x /= aspect; // aspect correction
	
	vec4 col = texture(image, disorsion + 0.5);
	
	#ifdef DARK_EDGES
	{
		float edge = 0.7;
		float dispersion = 0.03;
		col *= vec4(
			pow(max(edge-len, 0.0), 0.2),
			pow(max(edge-dispersion-len, 0.0), 0.2),
			pow(max(edge-dispersion*2.0-len, 0.0), 0.2),
		1)*1.2;
	}
	#endif

	return col;
}

But, instead of the same effect, I get this 🤦:

I think the main problem is about aspect. But I tried different things and I didn't arrive to anywhere.

Where is the error?

[Limeth]

Strange! Looks like "builtin_uv_size" has a bug!
It works fine for me when I set aspect = 16.0/9.0;, which is the aspect ratio of my source.

[MarioMey]

Yes, you are right: aspect = 16.0/9.0; does the trick.

It's a pity that we can't print any value to debug it...

[MarioMey]

Ok, fixed the aspect by @Limeth, I would want this shader to have some modifications. If anyone knows and wants to play a bit with it... 😁

• The ball/circle could be complete in screen, with no top/bottom crops.
• [DELETED, read EDIT]

With these modifications, we can move the source by the screen like a bubble.

[EDIT]: I change some code to make the ball opaque and the black ouside, transparent:

		col *= vec4(
			pow(max(edge-len, 0.0), 0.2),
			pow(max(edge-dispersion-len, 0.0), 0.2),
			pow(max(edge-dispersion*2.0-len, 0.0), 0.2),
			pow(max(edge-len, 0.0), 0.05))*1.2;