说在前面

• rust新手，egui没啥找到啥教程，这里自己记录下学习过程
• 环境：windows11 22H2
• rust版本：rustc 1.71.1
• egui版本：0.22.0
• eframe版本：0.22.0
• 上一篇：这里

painter

• 定义

  pub struct Painter {
      /// Source of fonts and destination of shapes
      ctx: Context,
  
      /// Where we paint
      layer_id: LayerId,
  
      /// Everything painted in this [`Painter`] will be clipped against this.
      /// This means nothing outside of this rectangle will be visible on screen.
      clip_rect: Rect,
  
      /// If set, all shapes will have their colors modified to be closer to this.
      /// This is used to implement grayed out interfaces.
      fade_to_color: Option<Color32>,
  }
  

• 我们可以使用painter来添加一个简单的矩形：

  egui::CentralPanel::default().show(ctx, |ui| {
  	// 从ui中指定一块区域
      let response =
      ui.allocate_rect(ui.available_rect_before_wrap(), egui::Sense::hover());
  	// 添加一个空Shape
      let shape = ui.painter().add(egui::Shape::Noop);
  	// 定义圆角大小
      let rounding = egui::Rounding::same(4.0);
      // 定义要绘制的矩形大小及位置
      let body_rect = egui::Rect::from_min_size(egui::pos2(10.0, 100.0), egui::vec2(100.0, 200.0));
      // 添加一个矩形
      let body = egui::Shape::Rect(egui::epaint::RectShape {
          rect: body_rect,
          rounding: rounding,
          fill: color_from_hex("#3f3f3f").unwrap(),
          stroke: egui::Stroke::NONE,
      });
  	// 绘制
      ui.painter().set(shape, body);
  });
  

  结果如下
  

绝对定位

• 虽然我们绘制出了一个矩形，但是它显示的位置却有些奇怪，这是因为我们使用的是绝对定位
• 我们使用矩形的左上、右下两个点来确定该矩形，如下图(10,100)、(110,300)，其宽100高200：
  
• 如果想要在我们的CentralPanel中绘制，需要进行转换：

  egui::CentralPanel::default().show(ctx, |ui| {
      let response = ui.allocate_rect(ui.available_rect_before_wrap(), egui::Sense::hover());
  	// 定义转换
      let to_screen = egui::emath::RectTransform::from_to(
          egui::Rect::from_min_size(egui::Pos2::ZERO, response.rect.size()),
          response.rect,
      );
  
      let shape = ui.painter().add(egui::Shape::Noop);
  
      let rounding_radius = 4.0;
      let rounding = egui::Rounding::same(rounding_radius);
      let mut body_rect =
          egui::Rect::from_min_size(egui::pos2(10.0, 100.0), egui::vec2(100.0, 200.0));
  
      // 进行转换
      body_rect = to_screen.transform_rect(body_rect);
      let body = egui::Shape::Rect(egui::epaint::RectShape {
          rect: body_rect,
          rounding: rounding,
          fill: color_from_hex("#3f3f3f").unwrap(),
          stroke: egui::Stroke::NONE,
      });
  
      ui.painter().set(shape, body);
  });
  

  
• 在转换后，我们的矩形为：
  

拖拽

• 在添加矩形后，我们可以对其进行拖拽：

  egui::CentralPanel::default().show(ctx, |ui| {
      let response = ui.allocate_rect(ui.max_rect(), egui::Sense::hover());
      let to_screen = egui::emath::RectTransform::from_to(
          egui::Rect::from_min_size(egui::Pos2::ZERO, response.rect.size()),
          response.rect,
      );
      let shape = ui.painter().add(egui::Shape::Noop);
      let rounding_radius = 4.0;
      let rounding = egui::Rounding::same(rounding_radius);
      let mut body_rect = egui::Rect::from_min_size(
          egui::Pos2 { x: 10.0, y: 100.0 },
          egui::vec2(100.0, 200.0),
      );
      body_rect = to_screen.transform_rect(body_rect);
      // 添加拖拽事件
      let window_response = ui.interact(
          body_rect,
          egui::Id::new((1, "window")),
          egui::Sense::click_and_drag(),
      );
      // 计算拖拽偏移量
      let drag_delta = window_response.drag_delta();
      if drag_delta.length_sq() > 0.0 {
      	// 移动矩形
          body_rect = body_rect.translate(drag_delta);
      }
      let body = egui::Shape::Rect(egui::epaint::RectShape {
          rect: body_rect,
          rounding: rounding,
          fill: color_from_hex("#3f3f3f").unwrap(),
          stroke: egui::Stroke::NONE,
      });
      ui.painter().set(shape, body);
  });
  

  
  但是好像拖不动，这是因为每次update的时候，我们定义的矩形位置都是固定的：

  let mut body_rect = egui::Rect::from_min_size(
          egui::Pos2 { x: 10.0, y: 100.0 },
          egui::vec2(100.0, 200.0),
      );
  

  因此我们需要记下上一次的位置：

  pub struct TemplateApp {
  	// ..
      // pos
      #[serde(skip)]
      rect_pos: egui::Pos2,
  }
  

  然后在创建矩形的时候使用上一次的位置：

  egui::CentralPanel::default().show(ctx, |ui| {
      let response = ui.allocate_rect(ui.max_rect(), egui::Sense::hover());
      let to_screen = egui::emath::RectTransform::from_to(
          egui::Rect::from_min_size(egui::Pos2::ZERO, response.rect.size()),
          response.rect,
      );
      let shape = ui.painter().add(egui::Shape::Noop);
      let rounding_radius = 4.0;
      let rounding = egui::Rounding::same(rounding_radius);
      let mut body_rect = egui::Rect::from_min_size(
          self.rect_pos,
          egui::vec2(100.0, 200.0),
      );
      body_rect = to_screen.transform_rect(body_rect);
      // 添加拖拽事件
      let window_response = ui.interact(
          body_rect,
          egui::Id::new((1, "window")),
          egui::Sense::click_and_drag(),
      );
      // 计算拖拽偏移量
      let drag_delta = window_response.drag_delta();
      if drag_delta.length_sq() > 0.0 {
      	// 移动矩形
          body_rect = body_rect.translate(drag_delta);
          // 改变初始位置
          self.rect_pos = self.rect_pos + drag_delta;
      }
      let body = egui::Shape::Rect(egui::epaint::RectShape {
          rect: body_rect,
          rounding: rounding,
          fill: color_from_hex("#3f3f3f").unwrap(),
          stroke: egui::Stroke::NONE,
      });
      ui.painter().set(shape, body);
  });
  

  

参考

• painter
• paint_bezier