Femtovg: Align the layer on the pixel grid

So that layer rendering is not blury

Author: ogoffart

internal/renderers/femtovg/itemrenderer.rs

@@ -1060,9 +1060,8 @@ impl<'a, R: femtovg::Renderer + TextureImporter> GLItemRenderer<'a, R> {
             });
 
         let cache_entry = self.graphics_cache.get_or_update_cache_entry(item_rc, || {
-            let bounding_rect = layer_bounding_rect_fn();
-            let origin = bounding_rect.origin * self.scale_factor;
-            let size = (bounding_rect.size * self.scale_factor).ceil().try_cast()?;
+            let bounding_rect = (layer_bounding_rect_fn() * self.scale_factor).round_out();
+            let size = bounding_rect.size.cast();
 
             let layer_image = existing_layer_texture
                 .and_then(|layer_texture| {
@@ -1094,11 +1093,11 @@ impl<'a, R: femtovg::Renderer + TextureImporter> GLItemRenderer<'a, R> {
 
                 canvas.clear_rect(0, 0, size.width, size.height, femtovg::Color::rgba(0, 0, 0, 0));
 
-                canvas.translate(-origin.x, -origin.y);
+                canvas.translate(-bounding_rect.origin.x, -bounding_rect.origin.y);
             }
 
             *self.state.last_mut().unwrap() = State {
-                scissor: bounding_rect,
+                scissor: bounding_rect / self.scale_factor,
                 global_alpha: 1.,
                 current_render_target: layer_image.as_render_target(),
             };
@@ -1119,7 +1118,10 @@ impl<'a, R: femtovg::Renderer + TextureImporter> GLItemRenderer<'a, R> {
                 canvas.set_render_target(previous_render_target);
             }
 
-            Some(ItemGraphicsCacheEntry::TextureWithOrigin { texture: layer_image, origin })
+            Some(ItemGraphicsCacheEntry::TextureWithOrigin {
+                texture: layer_image,
+                origin: bounding_rect.origin,
+            })
         });
 
         cache_entry.and_then(|item_cache_entry| match item_cache_entry {