bevy/crates/bevy_text/src/draw.rs

use bevy_math::{Mat4, Vec3};
use bevy_render::{
    color::Color,
    draw::{Draw, DrawContext, DrawError, Drawable},
    mesh,
    mesh::Mesh,
    pipeline::{PipelineSpecialization, VertexBufferDescriptor},
    prelude::Msaa,
    renderer::{BindGroup, RenderResourceBindings, RenderResourceId},
};
use bevy_sprite::TextureAtlasSprite;
use glyph_brush_layout::{HorizontalAlign, VerticalAlign};

use crate::PositionedGlyph;

#[derive(Debug, Clone, Copy)]
pub struct TextAlignment {
    pub vertical: VerticalAlign,
    pub horizontal: HorizontalAlign,
}

impl Default for TextAlignment {
    fn default() -> Self {
        TextAlignment {
            vertical: VerticalAlign::Top,
            horizontal: HorizontalAlign::Left,
        }
    }
}

#[derive(Clone, Debug)]
pub struct TextStyle {
    pub font_size: f32,
    pub color: Color,
    pub alignment: TextAlignment,
}

impl Default for TextStyle {
    fn default() -> Self {
        Self {
            color: Color::WHITE,
            font_size: 12.0,
            alignment: TextAlignment::default(),
        }
    }
}

pub struct DrawableText<'a> {
    pub render_resource_bindings: &'a mut RenderResourceBindings,
    pub position: Vec3,
    pub scale_factor: f32,
    pub style: &'a TextStyle,
    pub text_glyphs: &'a Vec<PositionedGlyph>,
    pub msaa: &'a Msaa,
    pub font_quad_vertex_descriptor: &'a VertexBufferDescriptor,
}

impl<'a> Drawable for DrawableText<'a> {
    fn draw(&mut self, draw: &mut Draw, context: &mut DrawContext) -> Result<(), DrawError> {
        context.set_pipeline(
            draw,
            &bevy_sprite::SPRITE_SHEET_PIPELINE_HANDLE.typed(),
            &PipelineSpecialization {
                sample_count: self.msaa.samples,
                vertex_buffer_descriptor: self.font_quad_vertex_descriptor.clone(),
                ..Default::default()
            },
        )?;

        let render_resource_context = &**context.render_resource_context;

        if let Some(RenderResourceId::Buffer(vertex_attribute_buffer_id)) = render_resource_context
            .get_asset_resource(
                &bevy_sprite::QUAD_HANDLE.typed::<Mesh>(),
                mesh::VERTEX_ATTRIBUTE_BUFFER_ID,
            )
        {
            draw.set_vertex_buffer(0, vertex_attribute_buffer_id, 0);
        } else {
            println!("Could not find vertex buffer for `bevy_sprite::QUAD_HANDLE`.")
        }

        let mut indices = 0..0;
        if let Some(RenderResourceId::Buffer(quad_index_buffer)) = render_resource_context
            .get_asset_resource(
                &bevy_sprite::QUAD_HANDLE.typed::<Mesh>(),
                mesh::INDEX_BUFFER_ASSET_INDEX,
            )
        {
            draw.set_index_buffer(quad_index_buffer, 0);
            if let Some(buffer_info) = render_resource_context.get_buffer_info(quad_index_buffer) {
                indices = 0..(buffer_info.size / 4) as u32;
            } else {
                panic!("Expected buffer type.");
            }
        }

        // set global bindings
        context.set_bind_groups_from_bindings(draw, &mut [self.render_resource_bindings])?;

        for tv in self.text_glyphs {
            context.set_asset_bind_groups(draw, &tv.atlas_info.texture_atlas)?;

            let sprite = TextureAtlasSprite {
                index: tv.atlas_info.glyph_index,
                color: self.style.color,
            };

            // To get the rendering right for non-one scaling factors, we need
            // the sprite to be drawn in "physical" coordinates. This is because
            // the shader uses the size of the sprite to control the size on
            // screen. To accomplish this we make the sprite transform
            // convert from physical coordinates to logical coordinates in
            // addition to altering the origin. Since individual glyphs will
            // already be in physical coordinates, we just need to convert the
            // overall position to physical coordinates to get the sprites
            // physical position.

            let transform = Mat4::from_scale(Vec3::splat(1. / self.scale_factor))
                * Mat4::from_translation(
                    self.position * self.scale_factor + tv.position.extend(0.),
                );

            let transform_buffer = context.get_uniform_buffer(&transform).unwrap();
            let sprite_buffer = context.get_uniform_buffer(&sprite).unwrap();
            let sprite_bind_group = BindGroup::build()
                .add_binding(0, transform_buffer)
                .add_binding(1, sprite_buffer)
                .finish();
            context.create_bind_group_resource(2, &sprite_bind_group)?;
            draw.set_bind_group(2, &sprite_bind_group);
            draw.draw_indexed(indices.clone(), 0, 0..1);
        }

        Ok(())
    }
}