Partial font texture update (#1149)

CHANGELOG.md

@@ -20,7 +20,9 @@ NOTE: [`epaint`](epaint/CHANGELOG.md), [`eframe`](eframe/CHANGELOG.md), [`egui_w
 * `Context` can now be cloned and stored between frames ([#1050](https://github.com/emilk/egui/pull/1050)).
 * Renamed `Ui::visible` to `Ui::is_visible`.
 * Split `Event::Text` into `Event::Text` and `Event::Paste` ([#1058](https://github.com/emilk/egui/pull/1058)).
-* For integrations: `FontImage` has been replaced by `TexturesDelta` (found in `Output`), describing what textures were loaded and freed each frame ([#1110](https://github.com/emilk/egui/pull/1110)).
+* For integrations:
+  * `FontImage` has been replaced by `TexturesDelta` (found in `Output`), describing what textures were loaded and freed each frame ([#1110](https://github.com/emilk/egui/pull/1110)).
+  * The painter must support partial texture updates ([#1149](https://github.com/emilk/egui/pull/1149)).
 
 ### Fixed 🐛
 * Context menu now respects the theme ([#1043](https://github.com/emilk/egui/pull/1043))

egui/src/context.rs

@@ -33,7 +33,6 @@ struct ContextImpl {
     fonts: Option<Fonts>,
     memory: Memory,
     animation_manager: AnimationManager,
-    latest_font_image_version: Option<u64>,
     tex_manager: WrappedTextureManager,
 
     input: InputState,
@@ -709,17 +708,15 @@ impl Context {
                 .memory
                 .end_frame(&ctx_impl.input, &ctx_impl.frame_state.used_ids);
 
-            let font_image = ctx_impl.fonts.as_ref().unwrap().font_image();
+            let font_image_delta = ctx_impl.fonts.as_ref().unwrap().font_image_delta();
-            let font_image_version = font_image.version;
+            if let Some(font_image_delta) = font_image_delta {
-
-            if Some(font_image_version) != ctx_impl.latest_font_image_version {
                 ctx_impl
                     .tex_manager
                     .0
                     .write()
-                    .set(TextureId::default(), font_image.image.clone().into());
+                    .set(TextureId::default(), font_image_delta);
-                ctx_impl.latest_font_image_version = Some(font_image_version);
             }
+
             ctx_impl
                 .output
                 .textures_delta
@@ -757,7 +754,7 @@ impl Context {
         let clipped_meshes = tessellator::tessellate_shapes(
             shapes,
             tessellation_options,
-            self.fonts().font_image().size(),
+            self.fonts().font_image_size(),
         );
         self.write().paint_stats = paint_stats.with_clipped_meshes(&clipped_meshes);
         clipped_meshes
@@ -961,8 +958,8 @@ impl Context {
             .show(ui, |ui| {
                 let mut font_definitions = self.fonts().definitions().clone();
                 font_definitions.ui(ui);
-                let font_image = self.fonts().font_image();
+                let font_image_size = self.fonts().font_image_size();
-                font_image.ui(ui);
+                crate::introspection::font_texture_ui(ui, font_image_size);
                 self.set_fonts(font_definitions);
             });
 

egui/src/introspection.rs

@@ -1,13 +1,16 @@
 //! uis for egui types.
 use crate::*;
 
-impl Widget for &epaint::FontImage {
+// Show font texture in demo Ui
-    fn ui(self, ui: &mut Ui) -> Response {
+pub(crate) fn font_texture_ui(ui: &mut Ui, [width, height]: [usize; 2]) -> Response {
     use epaint::Mesh;
 
     ui.vertical(|ui| {
-            // Show font texture in demo Ui
+        let color = if ui.visuals().dark_mode {
-            let [width, height] = self.size();
+            Color32::WHITE
+        } else {
+            Color32::BLACK
+        };
 
         ui.label(format!(
             "Texture size: {} x {} (hover to zoom)",
@@ -22,11 +25,7 @@ impl Widget for &epaint::FontImage {
         }
         let (rect, response) = ui.allocate_at_least(size, Sense::hover());
         let mut mesh = Mesh::default();
-            mesh.add_rect_with_uv(
+        mesh.add_rect_with_uv(rect, [pos2(0.0, 0.0), pos2(1.0, 1.0)].into(), color);
-                rect,
-                [pos2(0.0, 0.0), pos2(1.0, 1.0)].into(),
-                Color32::WHITE,
-            );
         ui.painter().add(Shape::mesh(mesh));
 
         let (tex_w, tex_h) = (width as f32, height as f32);
@@ -48,13 +47,12 @@ impl Widget for &epaint::FontImage {
                         pos2((u + texel_radius) / tex_w, (v + texel_radius) / tex_h),
                     );
                     let mut mesh = Mesh::default();
-                        mesh.add_rect_with_uv(zoom_rect, uv_rect, Color32::WHITE);
+                    mesh.add_rect_with_uv(zoom_rect, uv_rect, color);
                     ui.painter().add(Shape::mesh(mesh));
                 }
             });
     })
     .response
-    }
 }
 
 impl Widget for &mut epaint::text::FontDefinitions {

egui/src/widgets/plot/items/mod.rs

@@ -1087,9 +1087,13 @@ pub struct PlotImage {
 
 impl PlotImage {
     /// Create a new image with position and size in plot coordinates.
-    pub fn new(texture_id: impl Into<TextureId>, position: Value, size: impl Into<Vec2>) -> Self {
+    pub fn new(
+        texture_id: impl Into<TextureId>,
+        center_position: Value,
+        size: impl Into<Vec2>,
+    ) -> Self {
         Self {
-            position,
+            position: center_position,
             name: Default::default(),
             highlight: false,
             texture_id: texture_id.into(),

egui_demo_lib/benches/benchmark.rs

@@ -114,11 +114,7 @@ pub fn criterion_benchmark(c: &mut Criterion) {
         let text_shape = TextShape::new(egui::Pos2::ZERO, galley);
         c.bench_function("tessellate_text", |b| {
             b.iter(|| {
-                tessellator.tessellate_text(
+                tessellator.tessellate_text(fonts.font_image_size(), text_shape.clone(), &mut mesh);
-                    fonts.font_image().size(),
-                    text_shape.clone(),
-                    &mut mesh,
-                );
                 mesh.clear();
             })
         });

egui_demo_lib/src/apps/demo/plot_demo.rs

@@ -343,10 +343,7 @@ impl Widget for &mut ItemsDemo {
         let image = PlotImage::new(
             texture,
             Value::new(0.0, 10.0),
-            [
+            5.0 * vec2(texture.aspect_ratio(), 1.0),
-                ui.fonts().font_image().width() as f32 / 100.0,
-                ui.fonts().font_image().height() as f32 / 100.0,
-            ],
         );
 
         let plot = Plot::new("items_demo")

egui_glium/src/epi_backend.rs

@@ -70,8 +70,8 @@ pub fn run(app: Box<dyn epi::App>, native_options: &epi::NativeOptions) -> ! {
                 integration.update(display.gl_window().window());
             let clipped_meshes = integration.egui_ctx.tessellate(shapes);
 
-            for (id, image) in textures_delta.set {
+            for (id, image_delta) in textures_delta.set {
-                painter.set_texture(&display, id, &image);
+                painter.set_texture(&display, id, &image_delta);
             }
 
             // paint:

egui_glium/src/lib.rs

@@ -155,8 +155,8 @@ impl EguiGlium {
         let shapes = std::mem::take(&mut self.shapes);
         let mut textures_delta = std::mem::take(&mut self.textures_delta);
 
-        for (id, image) in textures_delta.set {
+        for (id, image_delta) in textures_delta.set {
-            self.painter.set_texture(display, id, &image);
+            self.painter.set_texture(display, id, &image_delta);
         }
 
         let clipped_meshes = self.egui_ctx.tessellate(shapes);

egui_glium/src/painter.rs

@@ -185,9 +185,9 @@ impl Painter {
         &mut self,
         facade: &dyn glium::backend::Facade,
         tex_id: egui::TextureId,
-        image: &egui::ImageData,
+        delta: &egui::epaint::ImageDelta,
     ) {
-        let pixels: Vec<(u8, u8, u8, u8)> = match image {
+        let pixels: Vec<(u8, u8, u8, u8)> = match &delta.image {
             egui::ImageData::Color(image) => {
                 assert_eq!(
                     image.width() * image.height(),
@@ -206,16 +206,30 @@ impl Painter {
         };
         let glium_image = glium::texture::RawImage2d {
             data: std::borrow::Cow::Owned(pixels),
-            width: image.width() as _,
+            width: delta.image.width() as _,
-            height: image.height() as _,
+            height: delta.image.height() as _,
             format: glium::texture::ClientFormat::U8U8U8U8,
         };
         let format = texture::SrgbFormat::U8U8U8U8;
         let mipmaps = texture::MipmapsOption::NoMipmap;
-        let gl_texture = SrgbTexture2d::with_format(facade, glium_image, format, mipmaps).unwrap();
 
+        if let Some(pos) = delta.pos {
+            // update a sub-region
+            if let Some(gl_texture) = self.textures.get(&tex_id) {
+                let rect = glium::Rect {
+                    left: pos[0] as _,
+                    bottom: pos[1] as _,
+                    width: glium_image.width,
+                    height: glium_image.height,
+                };
+                gl_texture.main_level().write(rect, glium_image);
+            }
+        } else {
+            let gl_texture =
+                SrgbTexture2d::with_format(facade, glium_image, format, mipmaps).unwrap();
             self.textures.insert(tex_id, gl_texture.into());
         }
+    }
 
     pub fn free_texture(&mut self, tex_id: egui::TextureId) {
         self.textures.remove(&tex_id);

egui_glow/src/epi_backend.rs

@@ -86,8 +86,8 @@ pub fn run(app: Box<dyn epi::App>, native_options: &epi::NativeOptions) -> ! {
                 integration.update(gl_window.window());
             let clipped_meshes = integration.egui_ctx.tessellate(shapes);
 
-            for (id, image) in textures_delta.set {
+            for (id, image_delta) in textures_delta.set {
-                painter.set_texture(&gl, id, &image);
+                painter.set_texture(&gl, id, &image_delta);
             }
 
             // paint:

egui_glow/src/lib.rs

@@ -175,8 +175,8 @@ impl EguiGlow {
         let shapes = std::mem::take(&mut self.shapes);
         let mut textures_delta = std::mem::take(&mut self.textures_delta);
 
-        for (id, image) in textures_delta.set {
+        for (id, image_delta) in textures_delta.set {
-            self.painter.set_texture(gl, id, &image);
+            self.painter.set_texture(gl, id, &image_delta);
         }
 
         let clipped_meshes = self.egui_ctx.tessellate(shapes);

egui_glow/src/painter.rs

@@ -340,6 +340,7 @@ impl Painter {
 
                 gl.bind_texture(glow::TEXTURE_2D, Some(texture));
             }
+
             // Transform clip rect to physical pixels:
             let clip_min_x = pixels_per_point * clip_rect.min.x;
             let clip_min_y = pixels_per_point * clip_rect.min.y;
@@ -386,7 +387,7 @@ impl Painter {
         &mut self,
         gl: &glow::Context,
         tex_id: egui::TextureId,
-        image: &egui::ImageData,
+        delta: &egui::epaint::ImageDelta,
     ) {
         self.assert_not_destroyed();
 
@@ -398,7 +399,7 @@ impl Painter {
             gl.bind_texture(glow::TEXTURE_2D, Some(glow_texture));
         }
 
-        match image {
+        match &delta.image {
             egui::ImageData::Color(image) => {
                 assert_eq!(
                     image.width() * image.height(),
@@ -408,7 +409,7 @@ impl Painter {
 
                 let data: &[u8] = bytemuck::cast_slice(image.pixels.as_ref());
 
-                self.upload_texture_srgb(gl, image.size, data);
+                self.upload_texture_srgb(gl, delta.pos, image.size, data);
             }
             egui::ImageData::Alpha(image) => {
                 assert_eq!(
@@ -427,12 +428,18 @@ impl Painter {
                     .flat_map(|a| a.to_array())
                     .collect();
 
-                self.upload_texture_srgb(gl, image.size, &data);
+                self.upload_texture_srgb(gl, delta.pos, image.size, &data);
             }
         };
     }
 
-    fn upload_texture_srgb(&mut self, gl: &glow::Context, [w, h]: [usize; 2], data: &[u8]) {
+    fn upload_texture_srgb(
+        &mut self,
+        gl: &glow::Context,
+        pos: Option<[usize; 2]>,
+        [w, h]: [usize; 2],
+        data: &[u8],
+    ) {
         assert_eq!(data.len(), w * h * 4);
         assert!(w >= 1 && h >= 1);
         unsafe {
@@ -457,38 +464,50 @@ impl Painter {
                 glow::TEXTURE_WRAP_T,
                 glow::CLAMP_TO_EDGE as i32,
             );
+            check_for_gl_error(gl, "tex_parameter");
 
-            if self.is_webgl_1 {
+            let (internal_format, src_format) = if self.is_webgl_1 {
                 let format = if self.srgb_support {
                     glow::SRGB_ALPHA
                 } else {
                     glow::RGBA
                 };
-                gl.tex_image_2d(
+                (format, format)
-                    glow::TEXTURE_2D,
-                    0,
-                    format as i32,
-                    w as i32,
-                    h as i32,
-                    0,
-                    format,
-                    glow::UNSIGNED_BYTE,
-                    Some(data),
-                );
             } else {
+                (glow::SRGB8_ALPHA8, glow::RGBA)
+            };
+
+            gl.pixel_store_i32(glow::UNPACK_ALIGNMENT, 1);
+
+            let level = 0;
+            if let Some([x, y]) = pos {
+                gl.tex_sub_image_2d(
+                    glow::TEXTURE_2D,
+                    level,
+                    x as _,
+                    y as _,
+                    w as _,
+                    h as _,
+                    src_format,
+                    glow::UNSIGNED_BYTE,
+                    glow::PixelUnpackData::Slice(data),
+                );
+                check_for_gl_error(gl, "tex_sub_image_2d");
+            } else {
+                let border = 0;
                 gl.tex_image_2d(
                     glow::TEXTURE_2D,
-                    0,
+                    level,
-                    glow::SRGB8_ALPHA8 as i32,
+                    internal_format as _,
-                    w as i32,
+                    w as _,
-                    h as i32,
+                    h as _,
-                    0,
+                    border,
-                    glow::RGBA,
+                    src_format,
                     glow::UNSIGNED_BYTE,
                     Some(data),
                 );
+                check_for_gl_error(gl, "tex_image_2d");
             }
-            check_for_gl_error(gl, "upload_texture_srgb");
         }
     }
 

egui_web/src/backend.rs

@@ -221,8 +221,8 @@ impl AppRunner {
     /// Paint the results of the last call to [`Self::logic`].
     pub fn paint(&mut self, clipped_meshes: Vec<egui::ClippedMesh>) -> Result<(), JsValue> {
         let textures_delta = std::mem::take(&mut self.textures_delta);
-        for (id, image) in textures_delta.set {
+        for (id, image_delta) in textures_delta.set {
-            self.painter.set_texture(id, image);
+            self.painter.set_texture(id, &image_delta);
         }
 
         self.painter.clear(self.app.clear_color());

egui_web/src/glow_wrapping.rs

@@ -40,8 +40,8 @@ impl WrappedGlowPainter {
 }
 
 impl crate::Painter for WrappedGlowPainter {
-    fn set_texture(&mut self, tex_id: egui::TextureId, image: egui::ImageData) {
+    fn set_texture(&mut self, tex_id: egui::TextureId, delta: &egui::epaint::ImageDelta) {
-        self.painter.set_texture(&self.glow_ctx, tex_id, &image);
+        self.painter.set_texture(&self.glow_ctx, tex_id, delta);
     }
 
     fn free_texture(&mut self, tex_id: egui::TextureId) {

egui_web/src/painter.rs

@@ -1,7 +1,7 @@
 use wasm_bindgen::prelude::JsValue;
 
 pub trait Painter {
-    fn set_texture(&mut self, tex_id: egui::TextureId, image: egui::ImageData);
+    fn set_texture(&mut self, tex_id: egui::TextureId, delta: &egui::epaint::ImageDelta);
 
     fn free_texture(&mut self, tex_id: egui::TextureId);
 

egui_web/src/webgl1.rs

@@ -40,13 +40,6 @@ impl WebGlPainter {
 
         // --------------------------------------------------------------------
 
-        let egui_texture = gl.create_texture().unwrap();
-        gl.bind_texture(Gl::TEXTURE_2D, Some(&egui_texture));
-        gl.tex_parameteri(Gl::TEXTURE_2D, Gl::TEXTURE_WRAP_S, Gl::CLAMP_TO_EDGE as i32);
-        gl.tex_parameteri(Gl::TEXTURE_2D, Gl::TEXTURE_WRAP_T, Gl::CLAMP_TO_EDGE as i32);
-        gl.tex_parameteri(Gl::TEXTURE_2D, Gl::TEXTURE_MIN_FILTER, Gl::LINEAR as i32);
-        gl.tex_parameteri(Gl::TEXTURE_2D, Gl::TEXTURE_MAG_FILTER, Gl::LINEAR as i32);
-
         let srgb_supported = matches!(gl.get_extension("EXT_sRGB"), Ok(Some(_)));
 
         let vert_shader = compile_shader(
@@ -222,36 +215,61 @@ impl WebGlPainter {
         Ok(())
     }
 
-    fn set_texture_rgba(&mut self, tex_id: egui::TextureId, size: [usize; 2], pixels: &[u8]) {
+    fn set_texture_rgba(
+        &mut self,
+        tex_id: egui::TextureId,
+        pos: Option<[usize; 2]>,
+        [w, h]: [usize; 2],
+        pixels: &[u8],
+    ) {
         let gl = &self.gl;
-        let gl_texture = gl.create_texture().unwrap();
+
-        gl.bind_texture(Gl::TEXTURE_2D, Some(&gl_texture));
+        let gl_texture = self
+            .textures
+            .entry(tex_id)
+            .or_insert_with(|| gl.create_texture().unwrap());
+
+        gl.bind_texture(Gl::TEXTURE_2D, Some(gl_texture));
         gl.tex_parameteri(Gl::TEXTURE_2D, Gl::TEXTURE_WRAP_S, Gl::CLAMP_TO_EDGE as _);
         gl.tex_parameteri(Gl::TEXTURE_2D, Gl::TEXTURE_WRAP_T, Gl::CLAMP_TO_EDGE as _);
         gl.tex_parameteri(Gl::TEXTURE_2D, Gl::TEXTURE_MIN_FILTER, Gl::LINEAR as _);
         gl.tex_parameteri(Gl::TEXTURE_2D, Gl::TEXTURE_MAG_FILTER, Gl::LINEAR as _);
 
-        gl.bind_texture(Gl::TEXTURE_2D, Some(&gl_texture));
-
         let level = 0;
         let internal_format = self.texture_format;
         let border = 0;
         let src_format = self.texture_format;
         let src_type = Gl::UNSIGNED_BYTE;
+
+        gl.pixel_storei(Gl::UNPACK_ALIGNMENT, 1);
+
+        if let Some([x, y]) = pos {
+            gl.tex_sub_image_2d_with_i32_and_i32_and_u32_and_type_and_opt_u8_array(
+                Gl::TEXTURE_2D,
+                level,
+                x as _,
+                y as _,
+                w as _,
+                h as _,
+                src_format,
+                src_type,
+                Some(pixels),
+            )
+            .unwrap();
+        } else {
             gl.tex_image_2d_with_i32_and_i32_and_i32_and_format_and_type_and_opt_u8_array(
                 Gl::TEXTURE_2D,
                 level,
                 internal_format as _,
-            size[0] as _,
+                w as _,
-            size[1] as _,
+                h as _,
                 border,
                 src_format,
                 src_type,
                 Some(pixels),
             )
             .unwrap();
-
+        }
-        self.textures.insert(tex_id, gl_texture);
     }
 }
 
@@ -271,8 +289,8 @@ impl epi::NativeTexture for WebGlPainter {
 }
 
 impl crate::Painter for WebGlPainter {
-    fn set_texture(&mut self, tex_id: egui::TextureId, image: egui::ImageData) {
+    fn set_texture(&mut self, tex_id: egui::TextureId, delta: &egui::epaint::ImageDelta) {
-        match image {
+        match &delta.image {
             egui::ImageData::Color(image) => {
                 assert_eq!(
                     image.width() * image.height(),
@@ -281,7 +299,7 @@ impl crate::Painter for WebGlPainter {
                 );
 
                 let data: &[u8] = bytemuck::cast_slice(image.pixels.as_ref());
-                self.set_texture_rgba(tex_id, image.size, data);
+                self.set_texture_rgba(tex_id, delta.pos, image.size, data);
             }
             egui::ImageData::Alpha(image) => {
                 let gamma = if self.post_process.is_none() {
@@ -293,7 +311,7 @@ impl crate::Painter for WebGlPainter {
                     .srgba_pixels(gamma)
                     .flat_map(|a| a.to_array())
                     .collect();
-                self.set_texture_rgba(tex_id, image.size, &data);
+                self.set_texture_rgba(tex_id, delta.pos, image.size, &data);
             }
         };
     }

egui_web/src/webgl2.rs

@@ -40,13 +40,6 @@ impl WebGl2Painter {
 
         // --------------------------------------------------------------------
 
-        let egui_texture = gl.create_texture().unwrap();
-        gl.bind_texture(Gl::TEXTURE_2D, Some(&egui_texture));
-        gl.tex_parameteri(Gl::TEXTURE_2D, Gl::TEXTURE_WRAP_S, Gl::CLAMP_TO_EDGE as i32);
-        gl.tex_parameteri(Gl::TEXTURE_2D, Gl::TEXTURE_WRAP_T, Gl::CLAMP_TO_EDGE as i32);
-        gl.tex_parameteri(Gl::TEXTURE_2D, Gl::TEXTURE_MIN_FILTER, Gl::LINEAR as i32);
-        gl.tex_parameteri(Gl::TEXTURE_2D, Gl::TEXTURE_MAG_FILTER, Gl::LINEAR as i32);
-
         let vert_shader = compile_shader(
             &gl,
             Gl::VERTEX_SHADER,
@@ -206,37 +199,61 @@ impl WebGl2Painter {
         Ok(())
     }
 
-    fn set_texture_rgba(&mut self, tex_id: egui::TextureId, size: [usize; 2], pixels: &[u8]) {
+    fn set_texture_rgba(
+        &mut self,
+        tex_id: egui::TextureId,
+        pos: Option<[usize; 2]>,
+        [w, h]: [usize; 2],
+        pixels: &[u8],
+    ) {
         let gl = &self.gl;
-        let gl_texture = gl.create_texture().unwrap();
+
-        gl.bind_texture(Gl::TEXTURE_2D, Some(&gl_texture));
+        let gl_texture = self
+            .textures
+            .entry(tex_id)
+            .or_insert_with(|| gl.create_texture().unwrap());
+
+        gl.bind_texture(Gl::TEXTURE_2D, Some(gl_texture));
         gl.tex_parameteri(Gl::TEXTURE_2D, Gl::TEXTURE_WRAP_S, Gl::CLAMP_TO_EDGE as _);
         gl.tex_parameteri(Gl::TEXTURE_2D, Gl::TEXTURE_WRAP_T, Gl::CLAMP_TO_EDGE as _);
         gl.tex_parameteri(Gl::TEXTURE_2D, Gl::TEXTURE_MIN_FILTER, Gl::LINEAR as _);
         gl.tex_parameteri(Gl::TEXTURE_2D, Gl::TEXTURE_MAG_FILTER, Gl::LINEAR as _);
 
-        gl.bind_texture(Gl::TEXTURE_2D, Some(&gl_texture));
-
         let level = 0;
         let internal_format = Gl::SRGB8_ALPHA8;
         let border = 0;
         let src_format = Gl::RGBA;
         let src_type = Gl::UNSIGNED_BYTE;
+
         gl.pixel_storei(Gl::UNPACK_ALIGNMENT, 1);
+
+        if let Some([x, y]) = pos {
+            gl.tex_sub_image_2d_with_i32_and_i32_and_u32_and_type_and_opt_u8_array(
+                Gl::TEXTURE_2D,
+                level,
+                x as _,
+                y as _,
+                w as _,
+                h as _,
+                src_format,
+                src_type,
+                Some(pixels),
+            )
+            .unwrap();
+        } else {
             gl.tex_image_2d_with_i32_and_i32_and_i32_and_format_and_type_and_opt_u8_array(
                 Gl::TEXTURE_2D,
                 level,
-            internal_format as i32,
+                internal_format as _,
-            size[0] as i32,
+                w as _,
-            size[1] as i32,
+                h as _,
                 border,
                 src_format,
                 src_type,
                 Some(pixels),
             )
             .unwrap();
-
+        }
-        self.textures.insert(tex_id, gl_texture);
     }
 }
 
@@ -256,8 +273,8 @@ impl epi::NativeTexture for WebGl2Painter {
 }
 
 impl crate::Painter for WebGl2Painter {
-    fn set_texture(&mut self, tex_id: egui::TextureId, image: egui::ImageData) {
+    fn set_texture(&mut self, tex_id: egui::TextureId, delta: &egui::epaint::ImageDelta) {
-        match image {
+        match &delta.image {
             egui::ImageData::Color(image) => {
                 assert_eq!(
                     image.width() * image.height(),
@@ -266,7 +283,7 @@ impl crate::Painter for WebGl2Painter {
                 );
 
                 let data: &[u8] = bytemuck::cast_slice(image.pixels.as_ref());
-                self.set_texture_rgba(tex_id, image.size, data);
+                self.set_texture_rgba(tex_id, delta.pos, image.size, data);
             }
             egui::ImageData::Alpha(image) => {
                 let gamma = 1.0;
@@ -274,7 +291,7 @@ impl crate::Painter for WebGl2Painter {
                     .srgba_pixels(gamma)
                     .flat_map(|a| a.to_array())
                     .collect();
-                self.set_texture_rgba(tex_id, image.size, &data);
+                self.set_texture_rgba(tex_id, delta.pos, image.size, &data);
             }
         };
     }

epaint/src/image.rs

@@ -211,6 +211,23 @@ impl AlphaImage {
             .iter()
             .map(move |&a| srgba_from_alpha_lut[a as usize])
     }
+
+    /// Clone a sub-region as a new image
+    pub fn region(&self, [x, y]: [usize; 2], [w, h]: [usize; 2]) -> AlphaImage {
+        assert!(x + w <= self.width());
+        assert!(y + h <= self.height());
+
+        let mut pixels = Vec::with_capacity(w * h);
+        for y in y..y + h {
+            let offset = y * self.width() + x;
+            pixels.extend(&self.pixels[offset..(offset + w)]);
+        }
+        assert_eq!(pixels.len(), w * h);
+        AlphaImage {
+            size: [w, h],
+            pixels,
+        }
+    }
 }
 
 impl std::ops::Index<(usize, usize)> for AlphaImage {
@@ -239,3 +256,45 @@ impl From<AlphaImage> for ImageData {
         Self::Alpha(image)
     }
 }
+
+// ----------------------------------------------------------------------------
+
+/// A change to an image.
+///
+/// Either a whole new image,
+/// or an update to a rectangular region of it.
+#[derive(Clone, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+#[must_use = "The painter must take care of this"]
+pub struct ImageDelta {
+    /// What to set the texture to.
+    pub image: ImageData,
+
+    /// If `None`, set the whole texture to [`Self::image`].
+    /// If `Some(pos)`, update a sub-region of an already allocated texture.
+    pub pos: Option<[usize; 2]>,
+}
+
+impl ImageDelta {
+    /// Update the whole texture.
+    pub fn full(image: impl Into<ImageData>) -> Self {
+        Self {
+            image: image.into(),
+            pos: None,
+        }
+    }
+
+    /// Update a sub-region of an existing texture.
+    pub fn partial(pos: [usize; 2], image: impl Into<ImageData>) -> Self {
+        Self {
+            image: image.into(),
+            pos: Some(pos),
+        }
+    }
+
+    /// Is this affecting the whole texture?
+    /// If `false`, this is a partial (sub-region) update.
+    pub fn is_whole(&self) -> bool {
+        self.pos.is_none()
+    }
+}

epaint/src/lib.rs

@@ -105,7 +105,7 @@ pub mod util;
 
 pub use {
     color::{Color32, Rgba},
-    image::{AlphaImage, ColorImage, ImageData},
+    image::{AlphaImage, ColorImage, ImageData, ImageDelta},
     mesh::{Mesh, Mesh16, Vertex},
     shadow::Shadow,
     shape::{CircleShape, PathShape, RectShape, Shape, TextShape},
@@ -113,7 +113,7 @@ pub use {
     stroke::Stroke,
     tessellator::{tessellate_shapes, TessellationOptions, Tessellator},
     text::{Fonts, Galley, TextStyle},
-    texture_atlas::{FontImage, TextureAtlas},
+    texture_atlas::TextureAtlas,
     texture_handle::TextureHandle,
     textures::TextureManager,
 };

epaint/src/text/font.rs

@@ -374,14 +374,12 @@ fn allocate_glyph(
         if glyph_width == 0 || glyph_height == 0 {
             UvRect::default()
         } else {
-            let glyph_pos = atlas.allocate((glyph_width, glyph_height));
+            let (glyph_pos, image) = atlas.allocate((glyph_width, glyph_height));
-
-            let image = atlas.image_mut();
             glyph.draw(|x, y, v| {
                 if v > 0.0 {
                     let px = glyph_pos.0 + x as usize;
                     let py = glyph_pos.1 + y as usize;
-                    image.image[(px, py)] = (v * 255.0).round() as u8;
+                    image[(px, py)] = (v * 255.0).round() as u8;
                 }
             });
 

epaint/src/text/fonts.rs

@@ -6,7 +6,7 @@ use crate::{
         font::{Font, FontImpl},
         Galley, LayoutJob,
     },
-    FontImage, TextureAtlas,
+    TextureAtlas,
 };
 
 // TODO: rename
@@ -233,11 +233,6 @@ pub struct Fonts {
     definitions: FontDefinitions,
     fonts: BTreeMap<TextStyle, Font>,
     atlas: Arc<Mutex<TextureAtlas>>,
-
-    /// Copy of the font image in the texture atlas.
-    /// This is so we can return a reference to it (the texture atlas is behind a lock).
-    buffered_font_image: Mutex<Arc<FontImage>>,
-
     galley_cache: Mutex<GalleyCache>,
 }
 
@@ -257,9 +252,9 @@ impl Fonts {
 
         {
             // Make the top left pixel fully white:
-            let pos = atlas.allocate((1, 1));
+            let (pos, image) = atlas.allocate((1, 1));
             assert_eq!(pos, (0, 0));
-            atlas.image_mut().image[pos] = 255;
+            image[pos] = 255;
         }
 
         let atlas = Arc::new(Mutex::new(atlas));
@@ -283,19 +278,11 @@ impl Fonts {
             })
             .collect();
 
-        {
-            let mut atlas = atlas.lock();
-            let texture = atlas.image_mut();
-            // Make sure we seed the texture version with something unique based on the default characters:
-            texture.version = crate::util::hash(&texture.image);
-        }
-
         Self {
             pixels_per_point,
             definitions,
             fonts,
             atlas,
-            buffered_font_image: Default::default(),
             galley_cache: Default::default(),
         }
     }
@@ -319,15 +306,14 @@ impl Fonts {
         (point * self.pixels_per_point).floor() / self.pixels_per_point
     }
 
-    /// Call each frame to get the latest available font texture data.
+    /// Call each frame to get the change to the font texture since last call.
-    pub fn font_image(&self) -> Arc<FontImage> {
+    pub fn font_image_delta(&self) -> Option<crate::ImageDelta> {
-        let atlas = self.atlas.lock();
+        self.atlas.lock().take_delta()
-        let mut buffered_texture = self.buffered_font_image.lock();
-        if buffered_texture.version != atlas.image().version {
-            *buffered_texture = Arc::new(atlas.image().clone());
     }
 
-        buffered_texture.clone()
+    /// Current size of the font image
+    pub fn font_image_size(&self) -> [usize; 2] {
+        self.atlas.lock().size()
     }
 
     /// Width of this character in points.

epaint/src/texture_atlas.rs

@@ -1,39 +1,40 @@
-use crate::image::AlphaImage;
+use crate::{AlphaImage, ImageDelta};
 
-/// An 8-bit texture containing font data.
+#[derive(Clone, Copy, Eq, PartialEq)]
-#[derive(Clone, Default)]
+struct Rectu {
-pub struct FontImage {
+    /// inclusive
-    /// e.g. a hash of the data. Use this to detect changes!
+    min_x: usize,
-    /// If the texture changes, this too will change.
+    /// inclusive
-    pub version: u64,
+    min_y: usize,
-
+    /// exclusive
-    /// The actual image data.
+    max_x: usize,
-    pub image: AlphaImage,
+    /// exclusive
+    max_y: usize,
 }
 
-impl FontImage {
+impl Rectu {
-    #[inline]
+    const NOTHING: Self = Self {
-    pub fn size(&self) -> [usize; 2] {
+        min_x: usize::MAX,
-        self.image.size
+        min_y: usize::MAX,
-    }
+        max_x: 0,
-
+        max_y: 0,
-    #[inline]
+    };
-    pub fn width(&self) -> usize {
+    const EVERYTHING: Self = Self {
-        self.image.size[0]
+        min_x: 0,
-    }
+        min_y: 0,
-
+        max_x: usize::MAX,
-    #[inline]
+        max_y: usize::MAX,
-    pub fn height(&self) -> usize {
+    };
-        self.image.size[1]
-    }
 }
 
 /// Contains font data in an atlas, where each character occupied a small rectangle.
 ///
 /// More characters can be added, possibly expanding the texture.
-#[derive(Clone, Default)]
+#[derive(Clone)]
 pub struct TextureAtlas {
-    image: FontImage,
+    image: AlphaImage,
+    /// What part of the image that is dirty
+    dirty: Rectu,
 
     /// Used for when allocating new rectangles.
     cursor: (usize, usize),
@@ -43,25 +44,35 @@ pub struct TextureAtlas {
 impl TextureAtlas {
     pub fn new(size: [usize; 2]) -> Self {
         Self {
-            image: FontImage {
-                version: 0,
             image: AlphaImage::new(size),
-            },
+            dirty: Rectu::EVERYTHING,
-            ..Default::default()
+            cursor: (0, 0),
+            row_height: 0,
         }
     }
 
-    pub fn image(&self) -> &FontImage {
+    pub fn size(&self) -> [usize; 2] {
-        &self.image
+        self.image.size
     }
 
-    pub fn image_mut(&mut self) -> &mut FontImage {
+    /// Call to get the change to the image since last call.
-        self.image.version += 1;
+    pub fn take_delta(&mut self) -> Option<ImageDelta> {
-        &mut self.image
+        let dirty = std::mem::replace(&mut self.dirty, Rectu::NOTHING);
+        if dirty == Rectu::NOTHING {
+            None
+        } else if dirty == Rectu::EVERYTHING {
+            Some(ImageDelta::full(self.image.clone()))
+        } else {
+            let pos = [dirty.min_x, dirty.min_y];
+            let size = [dirty.max_x - dirty.min_x, dirty.max_y - dirty.min_y];
+            let region = self.image.region(pos, size);
+            Some(ImageDelta::partial(pos, region))
+        }
     }
 
-    /// Returns the coordinates of where the rect ended up.
+    /// Returns the coordinates of where the rect ended up,
-    pub fn allocate(&mut self, (w, h): (usize, usize)) -> (usize, usize) {
+    /// and invalidates the region.
+    pub fn allocate(&mut self, (w, h): (usize, usize)) -> ((usize, usize), &mut AlphaImage) {
         /// On some low-precision GPUs (my old iPad) characters get muddled up
         /// if we don't add some empty pixels between the characters.
         /// On modern high-precision GPUs this is not needed.
@@ -81,21 +92,31 @@ impl TextureAtlas {
         }
 
         self.row_height = self.row_height.max(h);
-        resize_to_min_height(&mut self.image.image, self.cursor.1 + self.row_height);
+        if resize_to_min_height(&mut self.image, self.cursor.1 + self.row_height) {
+            self.dirty = Rectu::EVERYTHING;
+        }
 
         let pos = self.cursor;
         self.cursor.0 += w + PADDING;
-        self.image.version += 1;
+
-        (pos.0 as usize, pos.1 as usize)
+        self.dirty.min_x = self.dirty.min_x.min(pos.0);
+        self.dirty.min_y = self.dirty.min_y.min(pos.1);
+        self.dirty.max_x = self.dirty.max_x.max(pos.0 + w);
+        self.dirty.max_y = self.dirty.max_y.max(pos.1 + h);
+
+        (pos, &mut self.image)
     }
 }
 
-fn resize_to_min_height(image: &mut AlphaImage, min_height: usize) {
+fn resize_to_min_height(image: &mut AlphaImage, min_height: usize) -> bool {
     while min_height >= image.height() {
         image.size[1] *= 2; // double the height
     }
 
     if image.width() * image.height() > image.pixels.len() {
         image.pixels.resize(image.width() * image.height(), 0);
+        true
+    } else {
+        false
     }
 }

epaint/src/texture_handle.rs

@@ -1,7 +1,7 @@
 use crate::{
     emath::NumExt,
     mutex::{Arc, RwLock},
-    ImageData, TextureId, TextureManager,
+    ImageData, ImageDelta, TextureId, TextureManager,
 };
 
 /// Used to paint images.
@@ -66,7 +66,16 @@ impl TextureHandle {
 
     /// Assign a new image to an existing texture.
     pub fn set(&mut self, image: impl Into<ImageData>) {
-        self.tex_mngr.write().set(self.id, image.into());
+        self.tex_mngr
+            .write()
+            .set(self.id, ImageDelta::full(image.into()));
+    }
+
+    /// Assign a new image to a subregion of the whole texture.
+    pub fn set_partial(&mut self, pos: [usize; 2], image: impl Into<ImageData>) {
+        self.tex_mngr
+            .write()
+            .set(self.id, ImageDelta::partial(pos, image.into()));
     }
 
     /// width x height

epaint/src/textures.rs

@@ -1,4 +1,4 @@
-use crate::{image::ImageData, TextureId};
+use crate::{ImageData, ImageDelta, TextureId};
 use ahash::AHashMap;
 
 // ----------------------------------------------------------------------------
@@ -38,16 +38,19 @@ impl TextureManager {
             retain_count: 1,
         });
 
-        self.delta.set.insert(id, image);
+        self.delta.set.insert(id, ImageDelta::full(image));
         id
     }
 
-    /// Assign a new image to an existing texture.
+    /// Assign a new image to an existing texture,
-    pub fn set(&mut self, id: TextureId, image: ImageData) {
+    /// or update a region of it.
+    pub fn set(&mut self, id: TextureId, delta: ImageDelta) {
         if let Some(meta) = self.metas.get_mut(&id) {
-            meta.size = image.size();
+            if delta.is_whole() {
-            meta.bytes_per_pixel = image.bytes_per_pixel();
+                meta.size = delta.image.size();
-            self.delta.set.insert(id, image);
+                meta.bytes_per_pixel = delta.image.bytes_per_pixel();
+            }
+            self.delta.set.insert(id, delta);
         } else {
             crate::epaint_assert!(
                 false,
@@ -147,7 +150,7 @@ impl TextureMeta {
 #[must_use = "The painter must take care of this"]
 pub struct TexturesDelta {
     /// New or changed textures. Apply before painting.
-    pub set: AHashMap<TextureId, ImageData>,
+    pub set: AHashMap<TextureId, ImageDelta>,
 
     /// Texture to free after painting.
     pub free: Vec<TextureId>,