ShaderSelector V4

An easy framework for sending information to post processing shaders using commands in Minecraft.

What is this used for?

This resource pack includes a framework that lets commands communicate with post processing shaders, along with a simple example demonstrating how to use it.

Here is a video showcasing the demonstration features:

example_video.mp4

If you want to try it out yourself, install the resource pack and run one of these commands:

# Turn on greyscale
/particle entity_effect{color:-67174913} ~ ~1 ~

# Turn off greyscale
/particle entity_effect{color:-67175168} ~ ~1 ~

# Rotate screen by 90° (instant)
/particle entity_effect{color:-67175616} ~ ~1 ~

# Rotate screen back to normal (instant)
/particle entity_effect{color:-67175680} ~ ~1 ~

# Rotate screen to 180° (smooth with acceleration)
/particle entity_effect{color:-67175296} ~ ~1 ~

# Rotate screen back to normal (smooth)
/particle entity_effect{color:-67175424} ~ ~1 ~

The good thing about everything being controlled through particles is that the /particle command has an argument that lets you determine which players are able to see a particle.

For a detailed guide (in Russian) on how everything works and how to write your own effects, see GUIDE.md.

How does this work?

At its core, this framework is structured around a persistent data buffer defined in the transparency post effect pipeline. This buffer saves inputs given through commands and processes them to produce interpolated output values. The number of channels and how they are used can be changed, but in the given example the data buffer looks like this:

Column:      0              1              2              3              4
          ┌──────────┬──────────────┬──────────────┬──────────────┬──────────────┐
Row 0:    │ GameTime │              │              │              │              │
          ├──────────┼──────────────┼──────────────┼──────────────┼──────────────┤
Row 1:    │ Input    │ Start time   │ Acceleration │ Speed        │ Value        │  (channel 1: greyscale)
          ├──────────┼──────────────┼──────────────┼──────────────┼──────────────┤
Row 2:    │ Input    │ Start time   │ Acceleration │ Speed        │ Value        │  (channel 2: rotation)
          └──────────┴──────────────┴──────────────┴──────────────┴──────────────┘

Each row is responsible for one "channel" which controls one effect. Within a row:

• Column 0 (input) — saves the last received input: whether there has been an input (red), the operation (green), and the target value (blue).
• Column 1 (startTime) — captures the GameTime (in seconds) from when the target value last changed on this channel.
• Columns 2 and 3 (acceleration and speed) — used internally to manage smooth interpolation of the output value.
• Column 4 (output) — the interpolated value that moves toward the target. How it moves depends on the operation.

Columns 1–4 each store a single 32-bit float with bits split across the RGBA components. Use decodeColor(vec4 color) from shader_selector:utils.glsl to read them, or the convenience function readChannel(int channel) from shader_selector:data_reader.glsl:

float greyscale = readChannel(EXAMPLE_GREYSCALE_CHANNEL); // 0.0 – 1.0
float rotation = readChannel(EXAMPLE_ROTATION_CHANNEL);   // 0.0 – 1.0

How is a new channel defined?

All a channel needs is space on the data buffer. The buffer size is set in the targets list of assets/minecraft/post_effect/transparency.json. In the example there are 2 channels plus the internal GameTime row, so "height": 3 for both data and data_swap targets.

To add a channel:

1. In marker_settings.glsl, define a channel constant and add markers to LIST_MARKERS.
2. In transparency.json, increase height of data and data_swap.
3. In your shader, read the value with readChannel(MY_CHANNEL).

How do I give an input to a channel?

A "marker particle" is a particle whose color is recognized by the core shader, which then sends it to the post shader. Marker definitions live in assets/shader_selector/shaders/include/marker_settings.glsl.

A marker is defined by adding it to the LIST_MARKERS macro:

ADD_MARKER(<channel>, <green>, <alpha>, <operation>, <rate>)

A particle with the color (MARKER_RED, <green>, <any blue value>, <alpha>) will be recognized as a marker targeting the specified channel. MARKER_RED (254) is constant across all markers.

The blue value of the particle becomes the "target value" written to the data buffer.

The particle must use entity_effect because it requires control over all 4 RGBA channels (including alpha). The color is specified as a packed ARGB integer:

ARGB = -67239936 + green * 256 + value

For example, to set greyscale (green=253) to 100% (value=255):

ARGB = -67239936 + 253 * 256 + 255 = -67174913
/particle entity_effect{color:-67174913} ~ ~1 ~

Operations

The <operation> parameter controls how the channel's value follows the target:

Op	Name	Behavior	Rate parameter
0	Set	Instant. Speed reset to 0	Not used (0.0)
1	Constant velocity	Linear motion toward target	Speed (units/second)
2	Cyclic constant velocity	Like 1, but wraps 0.0–1.0 via shortest path	Speed
3	Accelerated motion	Smooth acceleration/deceleration toward target	Acceleration (units/second²)
4	Cyclic accelerated	Like 3, but wraps 0.0–1.0 via shortest path	Acceleration

Overflow (cyclic operations): Values wrap from 1.0 back to 0.0. To go from 0.9 to 0.1, the value adds 0.2 (wrapping through 1.0) rather than subtracting 0.8. Under overflow, the target is interpreted as blue/256 instead of blue/255, so values like 0.5 (128/256) are represented exactly.

Quick reference

Example markers (from default config)

Effect	green	op	rate	ARGB formula
Greyscale (smooth)	253	1	0.1	-67175168 + value
Rotation (instant)	251	0	0.0	-67175680 + value
Rotation (smooth cyclic)	252	4	0.4	-67175424 + value

Ready-to-use commands

Action	Command
Greyscale ON	particle entity_effect{color:-67174913} ~ ~1 ~
Greyscale OFF	particle entity_effect{color:-67175168} ~ ~1 ~
Greyscale 50%	particle entity_effect{color:-67175040} ~ ~1 ~
Rotation SET 0°	particle entity_effect{color:-67175680} ~ ~1 ~
Rotation SET 90°	particle entity_effect{color:-67175616} ~ ~1 ~
Rotation SET 180°	particle entity_effect{color:-67175552} ~ ~1 ~
Rotation SMOOTH 180°	particle entity_effect{color:-67175296} ~ ~1 ~
Rotation SMOOTH 0°	particle entity_effect{color:-67175424} ~ ~1 ~

History

This framework is based on a previous version. That version had been extracted into its own repository and popularized by CloudWolfYT to create ShaderSelectorV2. ShaderSelectorV3 was a complete rewrite, and V4 continues with these notable changes across versions:

• V2 used the post shader format from before Minecraft 1.21.2; V3 was developed in 24w38a (a 1.21.2 snapshot); V4 targets 26.1.
• The data sampler has a changed layout.
• Interpolation counts in real time instead of frames (rate is in units/second instead of units/frame).
• Every channel saves how much time passed since its target value was last changed.
• Apart from constant-rate interpolation, there is accelerated motion interpolation.
• Interpolation can use overflow (cyclic wrapping) for shortest-path transitions.
• Adding/editing a channel only requires changing marker_settings.glsl and adjusting the data buffer height in transparency.json.
• Added readChannel() convenience function via data_reader.glsl.