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Project Viewpoint Addon API

Shader values

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A shader value is a number that your addon sets on the main thread. Viewpoint gives it to shader code as a uniform. Use it to let a Shaderpack, a snippet or a Gpu program react to your addon, for example to the lean of a camera.

Permission: shaders.

permissions=shaders

Declare and set

Section titled “Declare and set”

Your addon declares each value with a name and a kind. Then it sets the value on the main thread. The kinds (ValueKind) are FLOAT, VEC2, VEC3, VEC4, INT and MAT4.

  • Declare each value when the addon starts. Set it on the main thread, as often as you want. Viewpoint copies the values into the frame once each frame, if one changed.
  • set takes as many numbers as the kind holds: 1 for FLOAT and INT, 2 to 4 for the vectors, 16 by columns for MAT4.
  • A pulse records the moment of an event. Shader code reads a vec2: the seconds since the last event, and its strength from 0 to 1. Before the first event, the seconds are 1,000,000.
  • An addon has 32 values and pulses at most.
LeanPart.java
ShaderValues values = ctx.shaders().values();
ShaderValue angle = values.declare("angle", ValueKind.FLOAT);
ShaderPulse step = values.pulse("step");


// Later, on the main thread:
angle.set(leanDegrees);
step.fire(0.6f);

Read it in GLSL

Section titled “Read it in GLSL”

The name of the uniform is uAddon_<encoded id>_<name>. The encoded id writes . and - as _.

uniform float uAddon_example_lean_angle;

For the addon example.lean and the value angle, this is the name above. Viewpoint sets the value on each Viewpoint program that declares the uniform. This includes:

  • the passes of a Shaderpack. See Passes & inputs;
  • the snippets of addons. See Shader snippets;
  • the programs that you make with Gpu. See Draw callbacks;
  • the programs of an Iris pack. Viewpoint binds the values by name for each program that declares them.

A program that does not declare the uniform gets nothing. A declared value that you have not set is 0. When your addon goes off, its values are 0 again.

Rules

Section titled “Rules”
  • A value name has letters and digits only, and it starts with a letter. Write it in camelCase, for example leanAngle. Viewpoint refuses any other name when you declare the value. Thus a name has one reading in GLSL.
  • Only your addon sets the values of your addon.
  • No addon code runs on the render thread to set a value. The values come in the snapshot of the frame.