ShaderInject

Veil provides a JSON-based shader injection system that allows modifying vanilla and pinwheel shaders without replacing the entire file. Injections are written as plain GLSL with a void tail() or void head() marker function.

Defining Injections

Injection definitions are located in assets/modid/pinwheel/shader_injection/*.json. Each definition references one or more GLSL files that contain the actual shader code.

JSON Format

{
  // The shader(s) to inject into. Can be a single string or array.
  "target": "minecraft:shaders/core/rendertype_solid.fsh",
  // The GLSL file(s) to inject. Required unless "replace" is used.
  "redirect": "modid:example.glsl",
  // Optional. Replace the target shader entirely with another Veil shader.
  // Mutually exclusive with redirect.
  "replace": "modid:custom_shader",
  // Optional. Lower values execute first. Default 1000.
  "priority": 1000,
  // Optional. Logs parsed body and globals for debugging.
  "debug": true
}

Fields

Field	Type	Default	Description
target	string or string[]	required	Shader(s) to inject into
redirect	string or string[]	see note	GLSL file(s) providing the injection code
replace	string	—	Replace the target shader entirely with another Veil shader
priority	int	1000	Injection order (lower = sooner)
debug	bool	false	Log injection body and globals to console

redirect and replace are mutually exclusive. One of them must be present.

Target Format

• redirect targets must include the shader extension (e.g. .fsh, .vsh):

  "target": "minecraft:shaders/core/rendertype_solid.fsh"
  

• replace targets do not include the extension:

  "target": "minecraft:shaders/core/rendertype_solid"
  

  The system strips shader extensions automatically for replace lookups.

Multi-Target Example

{
  "target": [
    "minecraft:shaders/core/rendertype_solid.vsh",
    "minecraft:shaders/core/rendertype_cutout.vsh"
  ],
  "redirect": "modid:scale.glsl"
}

Replace

replace completely swaps the target shader with another Veil shader program defined in pinwheel/shaders/program/. Unlike redirect, which injects code into the existing shader, replace discards the original entirely and substitutes a different ShaderProgram.

• The target must be a vanilla Minecraft shader (e.g. minecraft:shaders/core/rendertype_solid) without file extension.
• The replacement must be a valid Veil shader program ID.
• Only vanilla Minecraft shaders can be replaced. To replace a Veil shader, use redirect with head/tail injections.

{
  "target": "minecraft:shaders/core/rendertype_solid",
  "replace": "modid:custom_shader"
}

Full Examples

head_example

JSON (assets/modid/pinwheel/shader_injection/head_example.json):

{
  "target": "minecraft:shaders/core/rendertype_translucent.fsh",
  "redirect": "modid:head_example.glsl"
}

GLSL (assets/modid/pinwheel/shader_injection/head_example.glsl):

// Affects translucent blocks: water, stained glass, ice, slime blocks, honey blocks.
// Desaturates to grayscale.
void tail() {
    float gray = dot(fragColor.rgb, vec3(0.299, 0.587, 0.114));
    fragColor.rgb = vec3(gray);
}

tail_example

JSON (assets/modid/pinwheel/shader_injection/tail_example.json):

{
  "target": "minecraft:shaders/core/rendertype_cutout_mipped.fsh",
  "redirect": "modid:tail_example.glsl"
}

GLSL (assets/modid/pinwheel/shader_injection/tail_example.glsl):

// Affects mipmapped cutout blocks: leaves, powered rails, decorated pots.
// Inverts the red and green channels for a psychedelic look.
void tail() {
    fragColor.r = 1.0 - fragColor.r;
    fragColor.g = 1.0 - fragColor.g;
}

multi_target

JSON (assets/modid/pinwheel/shader_injection/multi_target.json):

{
  "target": [
    "minecraft:shaders/core/rendertype_entity_solid.fsh",
    "minecraft:shaders/core/rendertype_entity_cutout.fsh",
    "minecraft:shaders/core/rendertype_entity_translucent.fsh"
  ],
  "redirect": "modid:multi_target.glsl"
}

GLSL (assets/modid/pinwheel/shader_injection/multi_target.glsl):

// Affects all entity rendering: mobs, players, item entities, armor stands.
// Applies a red overlay to everything.
void tail() {
    fragColor.rgb = mix(fragColor.rgb, vec3(1.0, 0.0, 0.0), 0.3);
}

replace_example

Requires a color shader program in assets/modid/pinwheel/shaders/program/.

Program JSON (assets/modid/pinwheel/shaders/program/color.json):

{
  "vertex": "modid:color",
  "fragment": "modid:color"
}

Vertex (assets/modid/pinwheel/shaders/program/color.vsh):

layout(location = 0) in vec3 Position;
layout(location = 1) in vec2 UV0;
layout(location = 2) in vec2 UV1;
layout(location = 3) in vec2 UV2;
layout(location = 4) in vec4 Color;
layout(location = 5) in vec3 Normal;

uniform mat4 ModelViewMat;
uniform mat4 ProjMat;
uniform vec3 ChunkOffset;

out vec2 texCoord0;
out vec4 vertexColor;

void main() {
    vec3 pos = Position + ChunkOffset;
    gl_Position = ProjMat * ModelViewMat * vec4(pos, 1.0);
    texCoord0 = UV0;
    vertexColor = Color;
}

Fragment (assets/modid/pinwheel/shaders/program/color.fsh):

uniform sampler2D Sampler0;

in vec2 texCoord0;
in vec4 vertexColor;

out vec4 fragColor;

void main() {
    fragColor = vertexColor;
}

Injection JSON (assets/modid/pinwheel/shader_injection/replace_example.json):

{
  "target": "minecraft:shaders/core/rendertype_solid",
  "replace": "modid:color"
}

GLSL Format

Write standard GLSL. Use void tail() to inject at the end of the target function (usually main), or void head() to inject at the start.

void tail() {
    gl_Position = gl_Position * 2.0;
}

Warning: If neither void head() nor void tail() is present, the injection is silently skipped and a warning is logged. At least one marker function is required.

Globals

Code placed outside the marker function is treated as globals and injected at the top of the shader. This is useful for uniforms, helper functions, or shared variables.

vec4 tintColor(vec4 color) {
    return color * vec4(1.0, 0.5, 0.5, 1.0);
}

void tail() {
    fragColor = tintColor(fragColor);
}

Version

If your injection requires a specific GLSL version, add #version at the top of the file. It will be auto-detected and applied if the target shader's version is lower.

#version 330

void tail() {
    gl_Position = gl_Position * 2.0;
}

If omitted, the version is handled automatically.

Standard GLSL syntax is fully supported, including comments, control flow, multi-line statements, and nested blocks.

See Shader.md for #include

Migration from the Old Format

Old (.txt)	New (JSON + GLSL)
#version 330	Optional. Auto-detected from GLSL file if present.
#priority 1000	"priority": 1000 in JSON
#include modid:path	#include "path.glsl" in GLSL file
#replace modid:path	"replace": "modid:path" in JSON
[FUNCTION main(0) HEAD]	void head() { } in GLSL file
[FUNCTION main(0) TAIL]	void tail() { } in GLSL file
[OUTPUT], [UNIFORM], [GET_ATTRIBUTE]	Write directly as globals outside tail()/head()
#name placeholders	Use variables directly
assets/.../shader_modifiers/*.txt	assets/.../shader_injection/*.json