1 files changed, 242 insertions, 0 deletions
diff --git a/alacritty/src/renderer/graphics/draw.rs b/alacritty/src/renderer/graphics/draw.rs
new file mode 100644
index 00000000..e07cc078
--- /dev/null
+++ b/alacritty/src/renderer/graphics/draw.rs
@@ -0,0 +1,242 @@
+//! This module implements the functionality to render graphic textures
+//! in the display.
+//!
+//! [`RenderList`] is used to track graphics in the visible cells. When all
+//! cells in the grid are read, graphics are rendered using the positions
+//! found in those cells.
+
+use std::collections::BTreeMap;
+use std::mem::{self, MaybeUninit};
+
+use crate::display::content::RenderableCell;
+use crate::gl::{self, types::*};
+use crate::renderer::graphics::{shader, GraphicsRenderer};
+
+use alacritty_terminal::graphics::GraphicId;
+use alacritty_terminal::index::{Column, Line};
+use alacritty_terminal::term::SizeInfo;
+
+use log::trace;
+
+/// Position to render each texture in the grid.
+struct RenderPosition {
+    column: Column,
+    line: Line,
+    offset_x: u16,
+    offset_y: u16,
+}
+
+/// Track textures to be rendered in the display.
+#[derive(Default)]
+pub struct RenderList {
+    items: BTreeMap<GraphicId, RenderPosition>,
+}
+
+impl RenderList {
+    /// Detects if the cell contains a graphic, then add it to the render list.
+    ///
+    /// The graphic is added only the first time it is found in a cell.
+    #[inline]
+    pub fn update(&mut self, cell: &RenderableCell) {
+        if let Some(graphic) = &cell.graphic {
+            let graphic_id = graphic.graphic_id();
+            if self.items.contains_key(&graphic_id) {
+                return;
+            }
+
+            let render_item = RenderPosition {
+                column: cell.point.column,
+                line: Line(cell.point.line as i32),
+                offset_x: graphic.offset_x,
+                offset_y: graphic.offset_y,
+            };
+
+            self.items.insert(graphic_id, render_item);
+        }
+    }
+
+    /// Returns `true` if there are no items to render.
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.items.is_empty()
+    }
+
+    /// Builds a list of vertex for the shader program.
+    pub fn build_vertices(self, renderer: &GraphicsRenderer) -> Vec<shader::Vertex> {
+        use shader::VertexSide::{BottomLeft, BottomRight, TopLeft, TopRight};
+
+        let mut vertices = Vec::new();
+
+        for (graphics_id, render_item) in self.items {
+            let graphic_texture = match renderer.graphic_textures.get(&graphics_id) {
+                Some(tex) => tex,
+                None => continue,
+            };
+
+            vertices.reserve(6);
+
+            let vertex = shader::Vertex {
+                texture_id: graphic_texture.texture.0,
+                sides: TopLeft,
+                column: render_item.column.0 as GLuint,
+                line: render_item.line.0 as GLuint,
+                height: graphic_texture.height,
+                width: graphic_texture.width,
+                offset_x: render_item.offset_x,
+                offset_y: render_item.offset_y,
+                base_cell_height: graphic_texture.cell_height,
+            };
+
+            vertices.push(vertex);
+
+            for &sides in &[TopRight, BottomLeft, TopRight, BottomRight, BottomLeft] {
+                vertices.push(shader::Vertex { sides, ..vertex });
+            }
+        }
+
+        vertices
+    }
+
+    /// Draw graphics in the display, using the graphics rendering shader
+    /// program.
+    pub fn draw(self, renderer: &GraphicsRenderer, size_info: &SizeInfo) {
+        let vertices = self.build_vertices(renderer);
+
+        // Initialize the rendering program.
+        unsafe {
+            gl::BindBuffer(gl::ARRAY_BUFFER, renderer.program.vbo);
+            gl::BindVertexArray(renderer.program.vao);
+
+            gl::UseProgram(renderer.program.id);
+
+            gl::Uniform2f(
+                renderer.program.u_cell_dimensions,
+                size_info.cell_width(),
+                size_info.cell_height(),
+            );
+            gl::Uniform2f(
+                renderer.program.u_view_dimensions,
+                size_info.width(),
+                size_info.height(),
+            );
+
+            gl::BlendFuncSeparate(gl::SRC_ALPHA, gl::ONE_MINUS_SRC_ALPHA, gl::SRC_ALPHA, gl::ONE);
+        }
+
+        // Array for storing the batch to render multiple graphics in a single call to the
+        // shader program.
+        //
+        // Each graphic requires 6 vertices (2 triangles to make a rectangle), and we will
+        // never have more than `TEXTURES_ARRAY_SIZE` graphics in a single call, so we set
+        // the array size to the maximum value that we can use.
+        let mut batch = [MaybeUninit::uninit(); shader::TEXTURES_ARRAY_SIZE * 6];
+        let mut batch_size = 0;
+
+        macro_rules! send_batch {
+            () => {
+                #[allow(unused_assignments)]
+                if batch_size > 0 {
+                    trace!("Call glDrawArrays with {} items", batch_size);
+
+                    unsafe {
+                        gl::BufferData(
+                            gl::ARRAY_BUFFER,
+                            (batch_size * mem::size_of::<shader::Vertex>()) as isize,
+                            batch.as_ptr().cast(),
+                            gl::STREAM_DRAW,
+                        );
+
+                        gl::DrawArrays(gl::TRIANGLES, 0, batch_size as GLint);
+                    }
+
+                    batch_size = 0;
+                }
+            };
+        }
+
+        // In order to send textures to the shader program we need to get a _slot_
+        // for every texture associated to a graphic.
+        //
+        // We have `u_textures.len()` slots available in each execution of the
+        // shader.
+        //
+        // For each slot we need three values:
+        //
+        // - The texture unit for `glActiveTexture` (`GL_TEXTUREi`).
+        // - The uniform location for `textures[i]`.
+        // - The index `i`, used to set the value of the uniform.
+        //
+        // These values are generated using the `tex_slots_generator` iterator.
+        //
+        // A single graphic has 6 vertices. All vertices will use the same texture
+        // slot. To detect if a texture has already a slot, we only need to compare
+        // with the last texture (`last_tex_slot`) because all the vertices of a
+        // single graphic are consecutive.
+        //
+        // When all slots are occupied, or the batch array is full, the current
+        // batch is sent and the iterator is reset.
+        //
+        // This logic could be simplified using the [Bindless Texture extension],
+        // but it is not a core feature of any OpenGL version, so hardware support
+        // is uncertain.
+        //
+        // [Bindless Texture extension]: https://www.khronos.org/opengl/wiki/Bindless_Texture
+
+        let tex_slots_generator = (gl::TEXTURE0..=gl::TEXTURE31)
+            .zip(renderer.program.u_textures.iter())
+            .zip(0_u32..)
+            .map(|((tex_enum, &u_texture), index)| (tex_enum, u_texture, index));
+
+        let mut tex_slots = tex_slots_generator.clone();
+
+        // Keep the last allocated slot in a `(texture id, index)` tuple.
+        let mut last_tex_slot = (0, 0);
+
+        for mut vertex in vertices {
+            // Check if we can reuse the last texture slot.
+            if last_tex_slot.0 != vertex.texture_id {
+                last_tex_slot = loop {
+                    match tex_slots.next() {
+                        None => {
+                            // No more slots. Send the batch and reset the iterator.
+                            send_batch!();
+                            tex_slots = tex_slots_generator.clone();
+                        },
+
+                        Some((tex_enum, u_texture, index)) => {
+                            unsafe {
+                                gl::ActiveTexture(tex_enum);
+                                gl::BindTexture(gl::TEXTURE_2D, vertex.texture_id);
+                                gl::Uniform1i(u_texture, index as GLint);
+                            }
+
+                            break (vertex.texture_id, index);
+                        },
+                    }
+                };
+            }
+
+            vertex.texture_id = last_tex_slot.1;
+            batch[batch_size] = MaybeUninit::new(vertex);
+            batch_size += 1;
+
+            if batch_size == batch.len() {
+                send_batch!();
+            }
+        }
+
+        send_batch!();
+
+        // Reset state.
+        unsafe {
+            gl::BlendFunc(gl::SRC1_COLOR, gl::ONE_MINUS_SRC1_COLOR);
+
+            gl::ActiveTexture(gl::TEXTURE0);
+            gl::BindTexture(gl::TEXTURE_2D, 0);
+
+            gl::UseProgram(0);
+            gl::BindVertexArray(0);
+            gl::BindBuffer(gl::ARRAY_BUFFER, 0);
+        }
+    }
+}