Add image/svg support to iced_glow

https://github.com/iced-rs/iced/issues/674

Uses image/svg support in `iced_graphics`. The is not currently using an
atlas, and uses one texture/draw per image. This should be good enough
for now; supporting images with glow is better than not supporting them,
and if something else performs better, that improvement can be made
without any change to the public API.

glow/src/image.rs

@@ -0,0 +1,212 @@
+use crate::program::{self, Shader};
+use crate::Transformation;
+use glow::HasContext;
+use iced_graphics::layer;
+#[cfg(feature = "image_rs")]
+use std::cell::RefCell;
+
+pub use iced_graphics::triangle::{Mesh2D, Vertex2D};
+
+#[cfg(feature = "image_rs")]
+use iced_graphics::image::raster;
+
+#[cfg(feature = "svg")]
+use iced_graphics::image::vector;
+
+mod textures;
+use textures::{Entry, Textures};
+
+#[derive(Debug)]
+pub(crate) struct Pipeline {
+    program: <glow::Context as HasContext>::Program,
+    vertex_array: <glow::Context as HasContext>::VertexArray,
+    vertex_buffer: <glow::Context as HasContext>::Buffer,
+    transform_location: <glow::Context as HasContext>::UniformLocation,
+    textures: Textures,
+    #[cfg(feature = "image_rs")]
+    raster_cache: RefCell<raster::Cache<Textures>>,
+    #[cfg(feature = "svg")]
+    vector_cache: vector::Cache<Textures>,
+}
+
+impl Pipeline {
+    pub fn new(
+        gl: &glow::Context,
+        shader_version: &program::Version,
+    ) -> Pipeline {
+        let program = unsafe {
+            let vertex_shader = Shader::vertex(
+                gl,
+                shader_version,
+                include_str!("shader/common/image.vert"),
+            );
+            let fragment_shader = Shader::fragment(
+                gl,
+                shader_version,
+                include_str!("shader/common/image.frag"),
+            );
+
+            program::create(
+                gl,
+                &[vertex_shader, fragment_shader],
+                &[(0, "i_Position")],
+            )
+        };
+
+        let transform_location =
+            unsafe { gl.get_uniform_location(program, "u_Transform") }
+                .expect("Get transform location");
+
+        unsafe {
+            gl.use_program(Some(program));
+
+            let transform: [f32; 16] = Transformation::identity().into();
+            gl.uniform_matrix_4_f32_slice(
+                Some(&transform_location),
+                false,
+                &transform,
+            );
+
+            gl.use_program(None);
+        }
+
+        let vertex_buffer =
+            unsafe { gl.create_buffer().expect("Create vertex buffer") };
+        let vertex_array =
+            unsafe { gl.create_vertex_array().expect("Create vertex array") };
+
+        unsafe {
+            gl.bind_vertex_array(Some(vertex_array));
+            gl.bind_buffer(glow::ARRAY_BUFFER, Some(vertex_buffer));
+
+            let vertices = &[0u8, 0, 1, 0, 0, 1, 1, 1];
+            gl.buffer_data_size(
+                glow::ARRAY_BUFFER,
+                vertices.len() as i32,
+                glow::STATIC_DRAW,
+            );
+            gl.buffer_sub_data_u8_slice(
+                glow::ARRAY_BUFFER,
+                0,
+                bytemuck::cast_slice(vertices),
+            );
+
+            gl.enable_vertex_attrib_array(0);
+            gl.vertex_attrib_pointer_f32(
+                0,
+                2,
+                glow::UNSIGNED_BYTE,
+                false,
+                0,
+                0,
+            );
+
+            gl.bind_buffer(glow::ARRAY_BUFFER, None);
+            gl.bind_vertex_array(None);
+        }
+
+        Pipeline {
+            program,
+            vertex_array,
+            vertex_buffer,
+            transform_location,
+            textures: Textures::new(),
+            #[cfg(feature = "image_rs")]
+            raster_cache: RefCell::new(raster::Cache::default()),
+            #[cfg(feature = "svg")]
+            vector_cache: vector::Cache::default(),
+        }
+    }
+
+    #[cfg(feature = "image_rs")]
+    pub fn dimensions(
+        &self,
+        handle: &iced_native::image::Handle,
+    ) -> (u32, u32) {
+        self.raster_cache.borrow_mut().load(handle).dimensions()
+    }
+
+    pub fn draw(
+        &mut self,
+        mut gl: &glow::Context,
+        transformation: Transformation,
+        _scale_factor: f32,
+        images: &[layer::Image],
+    ) {
+        unsafe {
+            gl.use_program(Some(self.program));
+            gl.bind_vertex_array(Some(self.vertex_array));
+            gl.bind_buffer(glow::ARRAY_BUFFER, Some(self.vertex_buffer));
+        }
+
+        #[cfg(feature = "image_rs")]
+        let mut raster_cache = self.raster_cache.borrow_mut();
+        for image in images {
+            let (entry, bounds) = match &image {
+                #[cfg(feature = "image_rs")]
+                layer::Image::Raster { handle, bounds } => (
+                    raster_cache.upload(handle, &mut gl, &mut self.textures),
+                    bounds,
+                ),
+                #[cfg(not(feature = "image_rs"))]
+                layer::Image::Raster { handle: _, bounds } => (None, bounds),
+
+                #[cfg(feature = "svg")]
+                layer::Image::Vector { handle, bounds } => {
+                    let size = [bounds.width, bounds.height];
+                    (
+                        self.vector_cache.upload(
+                            handle,
+                            size,
+                            _scale_factor,
+                            &mut gl,
+                            &mut self.textures,
+                        ),
+                        bounds,
+                    )
+                }
+
+                #[cfg(not(feature = "svg"))]
+                layer::Image::Vector { handle: _, bounds } => (None, bounds),
+            };
+
+            unsafe {
+                if let Some(Entry { texture, .. }) = entry {
+                    gl.bind_texture(glow::TEXTURE_2D, Some(*texture))
+                } else {
+                    continue;
+                }
+
+                let translate = Transformation::translate(bounds.x, bounds.y);
+                let scale = Transformation::scale(bounds.width, bounds.height);
+                let transformation = transformation * translate * scale;
+                let matrix: [f32; 16] = transformation.into();
+                gl.uniform_matrix_4_f32_slice(
+                    Some(&self.transform_location),
+                    false,
+                    &matrix,
+                );
+
+                gl.draw_arrays(glow::TRIANGLE_STRIP, 0, 4);
+
+                gl.bind_texture(glow::TEXTURE_2D, None);
+            }
+        }
+
+        unsafe {
+            gl.bind_buffer(glow::ARRAY_BUFFER, None);
+            gl.bind_vertex_array(None);
+            gl.use_program(None);
+        }
+    }
+
+    pub fn trim_cache(&mut self, mut gl: &glow::Context) {
+        #[cfg(feature = "image_rs")]
+        self.raster_cache
+            .borrow_mut()
+            .trim(&mut self.textures, &mut gl);
+
+        #[cfg(feature = "svg")]
+        self.vector_cache.trim(&mut self.textures, &mut gl);
+    }
+}