[−][src]Module vulkano::descriptor

Provides a way for shaders to access the content of buffers and images, or read arbitrary data.

If you except vertex attributes, there are two ways in Vulkan to pass data to a shader:

You can pass a very small amount of data (only a guaranteed 128 bytes) through the push constants mechanism. Push constants are the fastest and easiest way to pass data.
You can make your shader read from a buffer or an image by binding it to a descriptor.

Here is an example fragment shader in GLSL that uses both:

#version 450

// This is a descriptor that contains a texture.
layout(set = 0, binding = 0) uniform sampler2D u_texture;

// This is a descriptor that contains a buffer.
layout(set = 0, binding = 1) uniform struct {
    int data[128];
} u_buffer;

layout(push_constant) uniform PushConstants {
    // This is a push constant.
    float opacity;
} push_constants;

layout(location = 0) in vec2 v_tex_coords;
layout(location = 0) out vec4 f_output;

void main() {
    f_output.rgb = texture(u_texture, v_tex_coords).rgb;
    if (u_buffer.data[12] == 5) { f_output.rgb *= 2.0; }
    f_output.a = push_constants.opacity;
}

Descriptors

In order to read the content of a buffer or an image from a shader, that buffer or image must be put in a descriptor. Each descriptor contains one buffer or one image alongside with the way that it can be accessed. A descriptor can also be an array, in which case it contains multiple buffers or images that all have the same layout.

Descriptors are grouped in what is called descriptor sets. In Vulkan you don't bind individual descriptors one by one, but you create then bind descriptor sets one by one. As binding a descriptor set has (small but non-null) a cost, you are encouraged to put descriptors that are often used together in the same set so that you can keep the same set binding through multiple draws.

Example

Note: This section describes the simple way to bind resources. There are more optimized ways.

There are two steps to give access to a resource in a shader: creating the descriptor set, and passing the descriptor sets when drawing.

Creating a descriptor set

// TODO: write example for: PersistentDescriptorSet::start(pipeline.clone(), 0).add_buffer(data_buffer.clone())

Passing the descriptor set when drawing

TODO: write

When drawing

When you call a function that adds a draw command to a command buffer, one of the parameters corresponds to the list of descriptor sets to use, and another parameter contains the push constants. Vulkano will check that what you passed is compatible with the layout of the compute or graphics pipeline.

TODO: talk about perfs of changing sets

Re-exports

pub use self::descriptor_set::DescriptorSet;

Modules

descriptor	Description of a single descriptor.
descriptor_set	Descriptor sets creation and management
pipeline_layout	A pipeline layout describes the layout of descriptors and push constants used by a graphics pipeline or a compute pipeline.

Traits

PipelineLayoutAbstract

Trait for objects that describe the layout of the descriptors and push constants of a pipeline.