fix: image appearing over alternate screen

src/gpu_types.rs

@@ -4,6 +4,19 @@
 //! All structures use `#[repr(C)]` and implement `bytemuck::Pod` for GPU compatibility.
 
 use bytemuck::{Pod, Zeroable};
+use std::sync::atomic::{AtomicU64, Ordering};
+
+/// Unique identifier for a pane.
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+pub struct PaneId(pub u64);
+
+impl PaneId {
+    /// Generate a new unique pane ID.
+    pub fn new() -> Self {
+        static COUNTER: std::sync::atomic::AtomicU64 = std::sync::atomic::AtomicU64::new(0);
+        Self(COUNTER.fetch_add(1, std::sync::atomic::Ordering::SeqCst))
+    }
+}
 
 // ═══════════════════════════════════════════════════════════════════════════════
 // CONSTANTS
@@ -148,8 +161,8 @@ pub struct ImageUniforms {
     pub src_y: f32,
     pub src_width: f32,
     pub src_height: f32,
+    pub dim_factor: f32,
     pub _padding1: f32,
-    pub _padding2: f32,
 }
 
 // ═══════════════════════════════════════════════════════════════════════════════