Uniforms

As described in the What is a Shader? page, uniform shaders simply are data that is constant for a single draw call, sent from the CPU to the GPU. In Kraken, uniform data can be stored and sent to the GPU using ShaderUniform-inherited objects.

Creating a Uniform Buffer

To create a uniform buffer, you need to define a class that inherits from ShaderUniform. Here's an example of a uniform buffer with commonly used data types:

class MyUniform(kn.ShaderUniform):
    value: float
    offset: tuple[float, float]
    color: tuple[float, float, float, float]

It can then be instantiated and updated like so:

my_uniform = MyUniform(value=1.0, offset=(0.0, 0.0), color=(1.0, 1.0, 1.0, 1.0))

# To update the uniform values
my_uniform.value = 2.5
my_uniform.offset = (10.0, 20.0)

Defining Uniforms in Shaders

In your shader code, you need to define the uniform buffer to match the structure of your ShaderUniform class. Here's how you would define the MyUniform in both HLSL and GLSL:

cbuffer MyUniform : register(b0, space3) {
    float value;
    float2 offset;
    float4 color;
};

Binding Uniforms

When creating a ShaderState, you need to specify the number of uniform buffers it will use. For example, if your shader uses one uniform buffer, you would create the ShaderState like this:

my_shader = kn.ShaderState(
    fragment_file_path="path/to/my_shader.frag.spv",
    uniform_buffer_count=1,  # One uniform buffer (MyUniform)
    sampler_count=1
)

Then, after binding the shader state, you can bind the uniform buffer to a specific binding point at any point (usually once per frame):

my_shader.set_uniform(binding=0, data=my_uniform.to_bytes())