Enum glium::draw_parameters::BackfaceCullingMode

pub enum BackfaceCullingMode {
    CullingDisabled,
    CullCounterClockwise,
    CullClockwise,
}

Describes how triangles should be filtered before the fragment processing. Backface culling is purely an optimization. If you don't know what this does, just use CullingDisabled.

Backface culling

After the vertex shader stage, the GPU knows the 2D coordinates of each vertex of each triangle.

For a given triangle, there are only two situations:

• The vertices are arranged in a clockwise direction on the screen.
• The vertices are arranged in a counterclockwise direction on the screen.

If you wish so, you can ask the GPU to discard all the primitives that belong to one of these two categories.

Example

The vertices of this triangle are counter-clock-wise.

Usage

The trick is that if you make a 180° rotation of a shape, all triangles that were clockwise become counterclockwise and vice versa.

Therefore you can arrange your model so that the triangles that are facing the screen are all either clockwise or counterclockwise, and all the triangle are not facing the screen are the other one.

By doing so you can use backface culling to discard all the triangles that are not facing the screen, and increase your framerate.

Variants

CullingDisabled

All triangles are always drawn.

CullCounterClockwise

Triangles whose vertices are counterclockwise won't be drawn.

CullClockwise

Triangles whose vertices are clockwise won't be drawn.

Trait Implementations

impl Eq for BackfaceCullingMode

impl PartialEq for BackfaceCullingMode

fn eq(&self, __arg_0: &BackfaceCullingMode) -> bool

This method tests for self and other values to be equal, and is used by ==.

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

This method tests for !=.

impl Debug for BackfaceCullingMode

fn fmt(&self, __arg_0: &mut Formatter) -> Result

Formats the value using the given formatter.

impl Copy for BackfaceCullingMode

impl Clone for BackfaceCullingMode

fn clone(&self) -> BackfaceCullingMode

Returns a copy of the value.

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

Performs copy-assignment from source.