Module glium::uniforms

A uniform is a global variable in your program. In order to draw something, you will need to give glium the values of all your uniforms. Objects that implement the Uniform trait are here to do that.

There are two primary ways to do this. The first one is to create your own structure and put the #[uniforms] attribute on it. See the glium_macros crate for more infos.

The second way is to use the uniform! macro provided by glium:

#[macro_use]
extern crate glium;

let uniforms = uniform! {
    texture: tex,
    matrix: matrix
};

In both situations, each field must implement the UniformValue trait.

Samplers

In order to customize the way a texture is being sampled, you must use a Sampler.

#[macro_use]
extern crate glium;

let uniforms = uniform! {
    texture: glium::uniforms::Sampler::new(&texture)
                        .magnify_filter(glium::uniforms::MagnifySamplerFilter::Nearest)
};

Blocks

In GLSL, you can choose to use a uniform block. When you use a block, you first need to upload the content of this block in the video memory thanks to a UniformBuffer. Then you can link the buffer to the name of the block, just like any other uniform.

#[macro_use]
extern crate glium;

let program = glium::Program::from_source(&display,
    "
        #version 110

        attribute vec2 position;

        void main() {
            gl_Position = vec4(position, 0.0, 1.0);
        }
    ",
    "
        #version 330
        uniform layout(std140);

        uniform MyBlock {
            vec3 color;
        };

        void main() {
            gl_FragColor = vec4(color, 1.0);
        }
    ",
    None);

let buffer = glium::uniforms::UniformBuffer::new(&display, (0.5f32, 0.5f32, 0.5f32)).unwrap();

let uniforms = uniform! {
    MyBlock: &buffer
};

Subroutines

OpenGL allows the use of subroutines, which are like function pointers. Subroutines can be used to change the functionality of a shader program at runtime. This method is usually a lot faster than using multiple programs that are switched during execution.

A subroutine uniform is unique per shader stage, and not per program.

#[macro_use]
extern crate glium;

let program = glium::Program::from_source(&display,
    "
        #version 150
        in vec2 position;
        void main() {
            gl_Position = vec4(position, 0.0, 1.0);
        }
    ",
    "
        #version 150
        #extension GL_ARB_shader_subroutine : require
        out vec4 fragColor;
        subroutine vec4 modify_t(vec4 color);
        subroutine uniform modify_t modify_color;

        subroutine(modify_t) vec4 delete_r(vec4 color)
        {
          return vec4(0, color.g, color.b, color.a);
        }

        subroutine(modify_t) vec4 delete_b(vec4 color)
        {
          return vec4(color.r, color.g, 0, color.a);
        }

        void main()
        {
            vec4 white= vec4(1, 1, 1, 1);
            fragColor = modify_color(white);
        }
    ", None);

    let uniforms = uniform! {
        modify_color: ("delete_b", glium::program::ShaderStage::Fragment)
    };

Structs

EmptyUniforms	Object that can be used when you don't have any uniforms.
Sampler	A sampler.
SamplerBehavior	Behavior of a sampler.
UniformBuffer	Buffer that contains a uniform block.
UniformsStorage	Stores uniforms.

Enums

DepthTextureComparison	The depth texture comparison operation to use when comparing the r value to the value in the currently bound texture.
LayoutMismatchError	Error about a block layout mismatch.
MagnifySamplerFilter	The function that the GPU will use when loading the value of a texel.
MinifySamplerFilter	The function that the GPU will use when loading the value of a texel.
SamplerWrapFunction	Function to use for out-of-bounds samples.
UniformType	Type of a uniform in a program.
UniformValue	Represents a value to bind to a uniform.

Traits

AsUniformValue	Value that can be used as the value of a uniform.
UniformBlock	Objects that are suitable for being inside a uniform block or a SSBO.
Uniforms	Object that contains the values of all the uniforms to bind to a program.