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use crate::core::*;
use crate::renderer::*;

///
/// A set of sprites, ie. a set of quads that orients itself towards the camera.
/// The sprites will always orient themselves towards the camera, but if a direction is specified, the sprite normals will also always be orthogonal to that direction.
/// For example, if the up direction is specified, the sprites will rotate around the up direction trying to face the camera.
/// Sprites are also known as billboards in the case where no direction is specified.
///
pub struct Sprites {
    context: Context,
    position_buffer: VertexBuffer,
    uv_buffer: VertexBuffer,
    center_buffer: InstanceBuffer,
    transformation: Mat4,
    direction: Option<Vec3>,
}

impl Sprites {
    ///
    /// Create a new set of [Sprites] with the given centers. The centers also determines the number of sprites.
    /// The sprites will always orient themselves towards the camera, but if a direction is specified, the sprite normals will always be orthogonal to that direction.
    ///
    pub fn new(context: &Context, centers: &[Vec3], direction: Option<Vec3>) -> ThreeDResult<Self> {
        let position_buffer = VertexBuffer::new_with_data(
            &context,
            &[
                vec3(-1.0, -1.0, 0.0),
                vec3(1.0, -1.0, 0.0),
                vec3(1.0, 1.0, 0.0),
                vec3(1.0, 1.0, 0.0),
                vec3(-1.0, 1.0, 0.0),
                vec3(-1.0, -1.0, 0.0),
            ],
        )?;
        let uv_buffer = VertexBuffer::new_with_data(
            &context,
            &[
                vec2(0.0, 0.0),
                vec2(1.0, 0.0),
                vec2(1.0, 1.0),
                vec2(1.0, 1.0),
                vec2(0.0, 1.0),
                vec2(0.0, 0.0),
            ],
        )?;
        Ok(Self {
            context: context.clone(),
            position_buffer,
            uv_buffer,
            center_buffer: InstanceBuffer::new_with_data(context, centers)?,
            transformation: Mat4::identity(),
            direction,
        })
    }

    ///
    /// Returns the local to world transformation applied to all sprites.
    ///
    pub fn transformation(&self) -> Mat4 {
        self.transformation
    }

    ///
    /// Set the local to world transformation applied to all sprites.
    ///
    pub fn set_transformation(&mut self, transformation: Mat4) {
        self.transformation = transformation;
    }

    ///
    /// Set a direction the sprite normals are always orthogonal to.
    ///
    pub fn set_direction(&mut self, direction: Option<Vec3>) {
        self.direction = direction;
    }

    ///
    /// Set the centers of the sprites. The centers also determines the number of sprites.
    ///
    pub fn set_centers(&mut self, centers: &[Vec3]) -> ThreeDResult<()> {
        self.center_buffer.fill(centers)
    }
}

impl Geometry for Sprites {
    fn render_with_material(
        &self,
        material: &dyn Material,
        camera: &Camera,
        lights: &[&dyn Light],
    ) -> ThreeDResult<()> {
        let fragment_shader_source = material.fragment_shader_source(false, lights);
        self.context.program(
            &include_str!("shaders/sprites.vert"),
            &fragment_shader_source,
            |program| {
                material.use_uniforms(program, camera, lights)?;
                program.use_uniform("eye", camera.position())?;
                program.use_uniform("viewProjection", camera.projection() * camera.view())?;
                program.use_uniform("transformation", self.transformation)?;
                program.use_vertex_attribute("position", &self.position_buffer)?;
                program.use_vertex_attribute("uv_coordinate", &self.uv_buffer)?;
                program.use_instance_attribute("center", &self.center_buffer)?;
                program.use_uniform("direction", self.direction.unwrap_or(vec3(0.0, 0.0, 0.0)))?;
                program.draw_arrays_instanced(
                    material.render_states(),
                    camera.viewport(),
                    6,
                    self.center_buffer.instance_count(),
                )
            },
        )
    }

    fn aabb(&self) -> AxisAlignedBoundingBox {
        AxisAlignedBoundingBox::INFINITE
    }
}