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I am writing Mandelbrot set shader for Unity.

I wrote an Image Effect shader and it works.

Unfortunately, each point "shimmers" on translate scale. This is because, for each shader call I compute value for only one mathematical point, which is infinitesimal. On even small translation, the value can change drastically.

So, I would like to compute math value not for one point, but for several. But for this I need to know, which aother points belong to my pixel, and for this I need to know the distance to neighbor pixel. Unfortunately, my incoming values are float and I don't know, how to step to next pixel.

How to accomplish?

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1 Answer 1

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Somewhere in your shader you'll have a declaration of your texture sampler, something like this:

sampler2D _MainTex; // This is the sampler.
float4 _MainTex_ST; // This is the scale/offset parameters set in the material widget.

Add one extra line below these:

float4 _MainTex_TexelSize;

This gives you a variable you can access in your shader, that Unity will pre-populate as described in the docs:

Texture size {TextureName}_TexelSize - a float4 property contains texture size information:

  • x contains 1.0/width
  • y contains 1.0/height
  • z contains width
  • w contains height

Now you can use this in your shader. Where the "current" pixel being drawn is...

float2 thisPixel = i.uv;

We can shift this to get...

float2 rightNeighbour  = i.uv + float2(_MainTex_TexelSize.x, 0);
float2 leftNeighbour   = i.uv - float2(_MainTex_TexelSize.x, 0);
float2 topNeighbour    = i.uv + float2(0, _MainTex_TexelSize.y);
float2 bottomNeighbour = i.uv - float2(0, _MainTex_TexelSize.y);

And of course you can scale this by a scalar to reach over only half a pixel, or two pixels, or combine both x & y to access a neighbouring point in any diagonal direction.

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  • \$\begingroup\$ Sorry, but this didn't work by some reason, don't understand why yet \$\endgroup\$
    – Dims
    Nov 3, 2020 at 21:33
  • \$\begingroup\$ What symptoms are you observing? How are you using this shader at present? The more information you can share, the better we can help you solve the problem. \$\endgroup\$
    – DMGregory
    Nov 3, 2020 at 21:34
  • \$\begingroup\$ Image started to duplicate with several "ghosts", as if docs about width and height is either incorrect or incomplete. Probably width and height are just 100 or something. Unfortunately, I don't know how to display the values from within shader. \$\endgroup\$
    – Dims
    Nov 3, 2020 at 21:38
  • \$\begingroup\$ The docs are correct, but the way you're using them might be incorrect. Try editing your question to walk us through all the steps needed to reproduce this problem in a new empty project. \$\endgroup\$
    – DMGregory
    Nov 3, 2020 at 21:39
  • \$\begingroup\$ Sure. Why is it saying about "texture" width and height? I have no texture at all. \$\endgroup\$
    – Dims
    Nov 4, 2020 at 8:39

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