Module 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.

The currently preferred way to do this is to use the uniform! macro provided by glium:

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

Each field must implement the UniformValue trait for this to work.

Samplers

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

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.

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.

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

• DynamicUniforms
  Stores Uniforms dynamicly in a HashMap.
• EmptyUniforms
  Object that can be used when you don’t have any uniforms.
• ImageUnit
  An image unit uniform marker
• ImageUnitBehavior
  How we bind a texture to an image unit
• 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.
• ImageUnitAccess
  States how the shader will access the image unit
• ImageUnitError
  Represents an error related to the use of an Image Unit
• ImageUnitFormat
  How the shader should interpret the data in the image
• 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.