# Shader: rendinst_parallax_ice

## Overview

As the name suggests, this shader is designed to simulate translucent ice using
parallax effects. It can be applied to both tiled textures, such as the surface
of a frozen lake, and unique assets, like a sculpted iceberg.

This shader blends two detail layers in a manner similar to the
[rendinst_perlin_layered](rendinst_perlin_layered.md) shader, but without
height-based gradients. A third detail layer is blended differently, using only
its diffuse texture, which is offset "into" the surface and refracted by the
normals of the mixed detail layers.

This shader uses a single UV channel, as
[rendinst_mask_layered](./dng-shaders/rendinst_mask_layered.md) does, and is
intended for relatively flat surfaces. Using it on organic shapes may cause
visual glitches, so it's recommended to make such areas opaque.

## Required Textures

- `tex0`: D1 Diffuse (RGB) + HeightMap (Alpha)
- `tex1`: Diffuse of the internal layer (RGB)
- `tex2`: D1 Normal (RG) + Glossiness (A)
- `tex3`: D2 Diffuse (RGB) + HeightMap (Alpha)
- `tex4`: D2 Normal (RG) + Glossiness (A)

## Optional Textures

- `tex5`: D1 transparency mask. If present, this mask is used for blending
  with the internal layer instead of the diffuse alpha. If a detail needs to be
  completely transparent or opaque, a black or white placeholder can be used.
- `tex6`: D2 transparency mask. Used similarly to `tex5`.
- `tex7`: Detail blending mask.

```{important}
All masks in `.folder.blk` must have `gamma=1` for correct operation.
```

- `VertexColor`: If available, this is used to force the internal layer to
  become opaque in black areas, while white areas remain unchanged. This is
  useful for handling the edges of ice chunks to avoid artifacts at corners.
  **Only the red channel is checked**, but for simplicity, it is shown as black
  and white in the example.

  <img src="_images/rendinst_parallax_ice_01.jpg" width="50%" align="center" class="bg-primary">

  <br>

## Parameters

**Color:**

- `inner_layer_depth`: Distance between the surface and the internal layer.
  `min=0.0` (no effect). Default: `0.1`

  <img src="_images/rendinst_parallax_ice_02.gif" width="50%" align="center" class="bg-primary">

  <br>

- `inner_layer_mul`: Multiplier for the internal layer's diffuse color,
  controlling brightness. Default: `1.0`

  <img src="_images/rendinst_parallax_ice_03.gif" width="50%" align="center" class="bg-primary">

  <br>

- `inner_layer_power`: Exponent that applied to the internal layer's color after
  multiplication, used to adjust contrast. Default: `1.0`

  <img src="_images/rendinst_parallax_ice_04.gif" width="50%" align="center" class="bg-primary">

  <br>

  Increasing both `power` and `mul` values can produce non-realistic but
  artistic effects, such as enhanced contrast and color saturation that give a
  glowing appearance. Use these settings sparingly. Here's an extreme example
  with `power=3` and `mul=3`:

  <img src="_images/rendinst_parallax_ice_05.jpg" width="50%" align="center" class="bg-primary">

  <br>

- `vcol_masked_mul`: Brightness multiplier for blended detail layers in areas
  marked white in VertexColor.
- `vcol_masked_power`: Contrast exponent for the same blended detail layers.

- `ior`: Index of refraction, controlling how much the normals of the detail
  layers distort the internal layer's diffuse. `min=1.0` (no effect), Default:
  `1.31`.

  Left to right: `ior=1.0` (no refraction), `1.31` (physically accurate for
  ice), and an exaggerated `4.0`. Other parameters, including `depth`, are
  identical.

  <img src="_images/rendinst_parallax_ice_06.jpg" width="80%" align="center" class="bg-primary">

  <br>

  By default, the shader uses a physically accurate value for ice, but you can
  adjust the `ior` to weaken or exaggerate the effect for visual purposes.
  Adjusting `depth` is also necessary, as increasing `ior` not only intensifies
  the internal layer's distortion by detail normals but also brings it visually
  closer to the surface.

  On the left: `ior=1.31` (default) and `depth=0.1`. On the right: `ior=4.0` and
  `depth=1`. These are not physically accurate, but they can be used for
  artistic effect. The internal layer becomes less distinct, which can sometimes
  be desirable.

<table style="text-align:center; width:98%"><tr>
  <th style="text-align:center; width:49%"><p>ior=1.31 and depth=0.1</p></th>
  <th style="text-align:center; width:49%"><p>ior=4.0 and depth=1</p></th></tr>
</table>

<img src="_images/rendinst_parallax_ice_07.gif" width="49%" class="bg-primary">
<img src="_images/rendinst_parallax_ice_08.gif" width="49%" class="bg-primary">

**Texture Coordinates:**

- `inner_layer_tile_uv`: Tiling of the internal layer.
- `inner_layer_u_offset`: Horizontal offset.
- `inner_layer_v_offset`: Vertical offset.

- `detail1_tile_uv`
- `detail1_u_offset`
- `detail1_v_offset`
- `modify_detail1_mask_uv`: Controls whether the transparency mask UVs for this
  detail are adjusted by the three parameters above. Default: `1`. This is
  useful if the mask was specifically painted for the asset, so tiling/offset
  adjustments don't break the mask.

- `detail2_tile_uv`
- `detail2_u_offset`
- `detail2_v_offset`
- `modify_detail2_mask_uv`

**Micro Details:**

- `micro_detail_layer1`: Index of the first micro detail layer.
- `micro_detail_layer1_uv_scale`: Tiling of the first micro detail layer.

- `micro_detail_layer2`: Index of the second micro detail layer.
- `micro_detail_layer2_uv_scale`: Tiling of the second micro detail layer.

**Masks:**

- `mask_gamma`: works the same way as in
  [rendinst_perlin_layered](./rendinst_perlin_layered.md). The first two values
  control the gamma of the detail masks, the third does nothing (since there is
  no third detail), and the fourth sets the tiling for the Perlin noise.
  Default: `1.0, 1.0, 0.0, 0.1`.
- `heightmaps_invert`: The first two values control the inversion of the detail
  blending masks, and the second pair controls the inversion of the transparency
  masks for those details. Default: `0,0, 0,0`.