1 files changed, 63 insertions, 0 deletions
diff --git a/games/rstnode/rst-client/src/viewport.rs b/games/rstnode/rst-client/src/viewport.rs
new file mode 100644
index 000000000000..3f9e803e387b
--- /dev/null
+++ b/games/rstnode/rst-client/src/viewport.rs
@@ -0,0 +1,63 @@
+//! Viewport utilities
+
+use crate::{graphics::Vector2, input::InputHandle};
+use ggez::{
+    error::GameResult,
+    graphics::{self, Rect},
+    Context,
+};
+
+#[derive(Default)]
+pub struct Viewport {
+    start: Vector2,
+    prev_start: Vector2,
+    size: Vector2,
+}
+
+impl Viewport {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    pub fn start(&self) -> &Vector2 {
+        &self.start
+    }
+
+    /// Must be called at least once before calling
+    /// [`update`](Self::update)
+    pub fn init(&mut self, ctx: &mut Context) {
+        let Rect { x, y, w, h } = graphics::screen_coordinates(&ctx);
+        self.start = Vector2::new(x, y);
+        self.prev_start = self.start;
+        self.size = Vector2::new(w, h);
+    }
+
+    /// Update the game state with the curent viewport data
+    pub fn update(&self, ctx: &mut Context) -> GameResult<()> {
+        graphics::set_screen_coordinates(
+            ctx,
+            Rect {
+                x: self.start.x,
+                y: self.start.y,
+                w: self.size.x,
+                h: self.size.y,
+            },
+        )?;
+
+        Ok(())
+    }
+
+    /// Apply changes from the input handle to the viewport
+    pub fn apply(&mut self, _: &mut Context, input: &InputHandle) -> GameResult<()> {
+        if input.middle_pressed {
+            let drag = input.drag_point.as_ref().unwrap().clone();
+            let pos = input.mouse_pos.clone();
+            self.start = self.prev_start + (drag - pos);
+            debug!("Changing VP start: {}", self.start);
+        } else {
+            self.prev_start = self.start;
+        }
+
+        Ok(())
+    }
+}