renderer: Allow clear calls on specific regions

CHANGELOG.md

@@ -31,6 +31,7 @@
 - `X11Surface::buffer` now additionally returns the age of the buffer
 - `X11Surface` now has an explicit `submit` function
 - `X11Surface` is now multi-window capable.
+- `Renderer::clear` now expects a second argument to optionally only clear parts of the buffer/surface
 
 ### Additions
 

anvil/src/render.rs

@@ -24,7 +24,7 @@ pub fn render_layers_and_windows(
     output_scale: f32,
     logger: &Logger,
 ) -> Result<(), SwapBuffersError> {
-    frame.clear([0.8, 0.8, 0.9, 1.0])?;
+    frame.clear([0.8, 0.8, 0.9, 1.0], None)?;
 
     for layer in [Layer::Background, Layer::Bottom] {
         draw_layers(

anvil/src/udev.rs

@@ -873,7 +873,7 @@ fn initial_render(surface: &mut RenderSurface, renderer: &mut Gles2Renderer) ->
     renderer
         .render((1, 1).into(), Transform::Normal, |_, frame| {
             frame
-                .clear([0.8, 0.8, 0.9, 1.0])
+                .clear([0.8, 0.8, 0.9, 1.0], None)
                 .map_err(Into::<SwapBuffersError>::into)
         })
         .map_err(Into::<SwapBuffersError>::into)

src/backend/renderer/gles2/mod.rs

@@ -1121,10 +1121,17 @@ impl Frame for Gles2Frame {
     type Error = Gles2Error;
     type TextureId = Gles2Texture;
 
-    fn clear(&mut self, color: [f32; 4]) -> Result<(), Self::Error> {
+    fn clear(&mut self, color: [f32; 4], at: Option<Rectangle<i32, Physical>>) -> Result<(), Self::Error> {
         unsafe {
+            if let Some(rect) = at {
+                self.gl.Enable(ffi::SCISSOR_TEST);
+                self.gl.Scissor(rect.loc.x, rect.loc.y, rect.size.w, rect.size.h);
+            }
             self.gl.ClearColor(color[0], color[1], color[2], color[3]);
             self.gl.Clear(ffi::COLOR_BUFFER_BIT);
+            if at.is_some() {
+                self.gl.Disable(ffi::SCISSOR_TEST);
+            }
         }
 
         Ok(())

src/backend/renderer/mod.rs

@@ -171,7 +171,7 @@ pub trait Frame {
     ///
     /// This operation is only valid in between a `begin` and `finish`-call.
     /// If called outside this operation may error-out, do nothing or modify future rendering results in any way.
-    fn clear(&mut self, color: [f32; 4]) -> Result<(), Self::Error>;
+    fn clear(&mut self, color: [f32; 4], at: Option<Rectangle<i32, Physical>>) -> Result<(), Self::Error>;
 
     /// Render a texture to the current target as a flat 2d-plane at a given
     /// position and applying the given transformation with the given alpha value.