Struct GlVertexArray

Source

pub struct GlVertexArray { /* private fields */ }

Expand description

A vertex array object: the recorded bundle of buffer bindings and vertex attribute formats.

Binding a VAO replaces up to a dozen bindBuffer / enableVertexAttribArray / vertexAttribPointer calls with one, which is what makes per-mesh draw state cheap enough to change on every draw call.

Implementations§

Source §

impl GlVertexArray

Implements vertex array binding and attribute description.

§Performance

Everything a draw needs to know about its vertex data, which buffer feeds which attribute at what stride and offset and how far each instance advances, is recorded once into the array object. A draw then costs one bindVertexArray instead of roughly three calls per attribute, which is what makes it affordable to change mesh between draws in the same frame.

Source

pub fn create(context: &WebGl2RenderingContext) -> Option<GlVertexArray>

Allocates an unbound vertex array object.

§Arguments

&WebGl2RenderingContext - The context to allocate against.

§Returns

Option<GlVertexArray> - The allocated array object, or None when the driver refused to create one.

Source

pub fn bind(&self, context: &WebGl2RenderingContext)

Makes the array object current, so subsequent attribute and buffer bindings are recorded into it rather than into the context’s default state.

§Arguments

&WebGl2RenderingContext - The context to bind against.

Source

pub fn set_layout( &self, context: &WebGl2RenderingContext, buffer: &GlBuffer, layout: &VertexBufferLayout, )

Binds buffer and describes every attribute in layout against it.

A layout whose step mode is Instance sets a per-attribute divisor of one, which is what makes WebGl2Backend::draw_elements_instanced advance the buffer once per instance rather than once per vertex. The divisor is set on every attribute rather than assumed fresh, because reusing an attribute index with a different step mode would otherwise inherit the previous divisor.

§Arguments

&WebGl2RenderingContext - The context to record into.
&GlBuffer - The buffer the attributes read from.
&VertexBufferLayout - The stride, step mode, and attribute list to record.

Source

pub fn set_instance_layout( &self, context: &WebGl2RenderingContext, buffer: &GlBuffer, layout: &VertexBufferLayout, )

Binds a second buffer and describes the attributes that read from it, leaving the ones already recorded alone.

The case a single buffer cannot express is a mesh whose positions advance per vertex while its per-instance transforms live in a separate buffer. One VAO records one array-buffer binding, so the second buffer is bound and described inside the same VAO.

§Arguments

&WebGl2RenderingContext - The context to record into.
&GlBuffer - The buffer the attributes read from.
&VertexBufferLayout - The attributes to record, whose step mode should be Instance.

Source

pub fn set_divisor( &self, context: &WebGl2RenderingContext, index: u32, divisor: u32, )

Records an explicit per-attribute divisor, overriding whatever the layout’s step mode implied.

§Arguments

&WebGl2RenderingContext - The context to record into.
u32 - The attribute index, as recorded on the layout.
u32 - The divisor: zero per vertex, one per instance.

Source

pub fn unbind(context: &WebGl2RenderingContext)

Unbinds the array object, restoring the context’s default vertex state.

Worth calling before a draw that reads no vertex data at all, a full-screen triangle generated from gl_VertexID say, because leaving an array object bound would keep its attribute buffers alive in the driver’s state.