Move text layout and rendering to Parley

core/src/primitive/texture.rs

@@ -29,14 +29,25 @@ pub struct Textures {
 pub enum TextureUpdate<'a> {
     Push(&'a DynamicImage),
     Set(u32, &'a DynamicImage),
+    /// Overwrite one rectangle without uploading the entire texture.
+    Patch(u32, PatchRect, &'a DynamicImage),
     Free(u32),
     PushFree,
     SetFree,
 }
 
+#[derive(Debug, Clone, Copy)]
+pub struct PatchRect {
+    pub x: u32,
+    pub y: u32,
+    pub width: u32,
+    pub height: u32,
+}
+
 enum Update {
     Push(u32),
     Set(u32),
+    Patch(u32, PatchRect),
     Free(u32),
 }
 
@@ -81,6 +92,19 @@ impl Textures {
         }
     }
 
+    /// The stored image for a handle, to be written into before `patch`.
+    pub fn image_mut(&mut self, handle: &TextureHandle) -> &mut DynamicImage {
+        self.images[handle.inner.view_idx as usize]
+            .as_mut()
+            .expect("texture was freed while still held")
+    }
+
+    /// Queue an upload of just `rect`, after writing it with `image_mut`.
+    pub fn patch(&mut self, handle: &TextureHandle, rect: PatchRect) {
+        self.updates
+            .push(Update::Patch(handle.inner.view_idx, rect));
+    }
+
     pub fn free(&mut self) {
         for idx in self.recv.try_iter() {
             self.images[idx as usize] = None;
@@ -99,6 +123,10 @@ impl Textures {
                 .as_ref()
                 .map(|img| TextureUpdate::Set(i, img))
                 .unwrap_or(TextureUpdate::SetFree),
+            Update::Patch(i, rect) => self.images[i as usize]
+                .as_ref()
+                .map(|img| TextureUpdate::Patch(i, rect, img))
+                .unwrap_or(TextureUpdate::SetFree),
             Update::Free(i) => TextureUpdate::Free(i),
         })
     }