Enum ClipRole 

pub enum ClipRole {
    Content,
    Narrow,
    Widen,
}

What a draw does with the stencil buffer.

Why the stencil holds a depth rather than a mask

The obvious encoding gives each clip a bit, which caps nesting at eight and makes intersecting two clips a per-bit affair. Storing the nesting depth instead lets a clip stack of any size fit in the same eight bits, and makes the test a single comparison: content belongs to depth d and draws where the stencil holds d, which is true only where every clip down to that depth admitted the pixel.

It also makes undoing a clip a local operation. Because a stack unwinds in the order it was built, no pixel can hold more than the depth being left, so stepping back is a decrement rather than a recomputation from the remaining clips.

Variants

Content

Draw color where the stencil already matches. Leaves the stencil alone.

Narrow

Narrow the clip: step the stencil forward where it matches and this draw covers. Writes no color.

The geometry must be a triangulation of the clip region rather than an overlapping set, since a pixel covered twice would step forward twice and stop matching anything. The fill tessellator produces exactly that, which is what lets this be a plain increment instead of the parity trick an overlapping fan would need.

Widen

Widen the clip back: step the stencil back where it matches. Writes no color.

Implementations

impl ClipRole

pub const fn writes_color(self) -> bool

Whether this role writes to the color attachment.

pub const fn writes_stencil(self) -> bool

Whether this role modifies the stencil.

Trait Implementations

impl Clone for ClipRole

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for ClipRole

impl Debug for ClipRole

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for ClipRole

fn default() -> Self

Returns the “default value” for a type.

impl Eq for ClipRole

impl Hash for ClipRole

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for ClipRole

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for ClipRole