Rewrite builder in the readme

This commit is contained in:
Maik Klein 2019-03-20 10:37:55 +01:00
parent 57859ba79d
commit bd2f990100

View file

@ -72,15 +72,50 @@ let desc_alloc_info = vk::DescriptorSetAllocateInfo {
};
```
### Builder pattern
```Rust
let pipeline_vertex_input_state_create_info = vk::PipelineVertexInputStateCreateInfo::builder()
.vertex_binding_descriptions(&Vertex::binding_descriptions())
.vertex_attribute_descriptions(&Vertex::attribute_descriptions()).build();
// We lose all lifetime information when we call `.build()`. Be carefull!
let queue_info = [vk::DeviceQueueCreateInfo::builder()
.queue_family_index(queue_family_index)
.queue_priorities(&priorities)
.build()];
// We don't need to call build here because builders implement `Deref`.
let device_create_info = vk::DeviceCreateInfo::builder()
.queue_create_infos(&queue_info)
.enabled_extension_names(&device_extension_names_raw)
.enabled_features(&features);
let device: Device = instance
.create_device(pdevice, &device_create_info, None)
.unwrap();
```
Builders implement `Deref` targeting their corresponding Vulkan struct, so references to builders can be passed directly
to Vulkan functions. This is encouraged as doing so allows Rust to check the lifetimes of captured objects are valid,
whereas calling `build` discards lifetime information, making inadvertent use-after-free errors more likely.
Builders have an explicit lifetime, and are marked as `#[repr(transparent)]`.
```Rust
#[repr(transparent)]
pub struct DeviceCreateInfoBuilder<'a> {
inner: DeviceCreateInfo,
marker: ::std::marker::PhantomData<&'a ()>,
}
impl<'a> DeviceCreateInfoBuilder<'a> {
//...
pub fn queue_create_infos(
mut self,
queue_create_infos: &'a [DeviceQueueCreateInfo],
) -> DeviceCreateInfoBuilder<'a> {
self.inner.queue_create_info_count = queue_create_infos.len() as _;
self.inner.p_queue_create_infos = queue_create_infos.as_ptr();
self
}
//...
```
Every reference has to live as long as the builder itself. Builders implement `Deref` targeting their corresponding Vulkan struct, so references to builders can be passed directly
to Vulkan functions.
Calling `.build()` will **discard** that lifetime because Vulkan structs use raw pointers internally. This should be avoided as much as possible because this can easily lead to dangling pointers.
### Pointer chains