A descriptor layout is a collection describing the content of a descriptor set. Each resource is specified by his binding number, a resources type and a number of element.

There is three types of layouts :

Generic layout used for vireo::DescriptorType::UNIFORM, vireo::DescriptorType::SAMPLED_IMAGE and vireo::DescriptorType::READWRITE_IMAGE resources
Samplers only for a collection of vireo::DescriptorType::SAMPLER resources
Dynamic Uniform for a single vireo::DescriptorType::UNIFORM_DYNAMIC resource

The samplers and dynamic uniform types of layouts exists for the sole reason of portability across graphics API.

A descriptor layout can be used to create multiple descriptor sets and for multiple pipelines. For example you can have in your application only one descriptor layout with all the needed samplers for all the pipelines.

Creating a descriptor layout

Descriptor layouts are created using vireo::Vireo::createDescriptorLayout, vireo::Vireo::createSamplerDescriptorLayout or vireo::Vireo::createDynamicUniformDescriptorLayout.

For generic and samplers layouts add resources descriptions with vireo::DescriptorLayout::add then build the layout with vireo::DescriptorLayout::build. For dynamic uniform layouts the add and build process is done automatically and the uniform buffer is bound to the index 0.

...
static constexpr vireo::DescriptorIndex BINDING_GLOBAL{0};
static constexpr vireo::DescriptorIndex BINDING_LIGHT{1};
static constexpr vireo::DescriptorIndex BINDING_TEXTURES{2};
...
 
descriptorLayout = vireo->createDescriptorLayout();
descriptorLayout->add(BINDING_GLOBAL, vireo::DescriptorType::UNIFORM);
descriptorLayout->add(BINDING_LIGHT, vireo::DescriptorType::UNIFORM);
descriptorLayout->add(BINDING_TEXTURES, vireo::DescriptorType::SAMPLED_IMAGE, scene.getTextures().size());
descriptorLayout->build();
 
materialsDescriptorLayout = vireo->createDynamicUniformDescriptorLayout();