Draw optimization

src/render/model_clip_iterator.rs

@@ -0,0 +1,64 @@
+use std::slice::Iter;
+use cairo;
+
+use super::context::CellMetrics;
+use ui_model;
+
+pub struct ModelClipIterator<'a> {
+    model_idx: usize,
+    model_iter: Iter<'a, ui_model::Line>,
+}
+
+pub trait ModelClipIteratorFactory {
+    fn get_clip_iterator(
+        &self,
+        ctx: &cairo::Context,
+        cell_metrics: &CellMetrics,
+    ) -> ModelClipIterator;
+}
+
+impl<'a> Iterator for ModelClipIterator<'a> {
+    type Item = (usize, &'a ui_model::Line);
+
+    fn next(&mut self) -> Option<(usize, &'a ui_model::Line)> {
+        let next = if let Some(line) = self.model_iter.next() {
+            Some((self.model_idx, line))
+        } else {
+            None
+        };
+        self.model_idx += 1;
+
+        next
+    }
+}
+
+/// Clip implemented as top - 1/bot + 1
+/// this is because in some cases(like 'g' character) drawing character does not fit to calculated bounds
+/// and if one line must be repainted - also previous and next line must be repainted to
+impl ModelClipIteratorFactory for ui_model::UiModel {
+    fn get_clip_iterator(
+        &self,
+        ctx: &cairo::Context,
+        cell_metrics: &CellMetrics,
+    ) -> ModelClipIterator {
+        let model = self.model();
+
+        let (x1, y1, x2, y2) = ctx.clip_extents();
+        let model_clip = ui_model::ModelRect::from_area(cell_metrics, x1, y1, x2, y2);
+        let model_clip_top = if model_clip.top <= 0 {
+            0
+        } else {
+            model_clip.top - 1
+        };
+        let model_clip_bot = if model_clip.bot >= model.len() - 1 {
+            model.len() - 1
+        } else {
+            model_clip.bot + 1
+        };
+
+        ModelClipIterator {
+            model_idx: model_clip_top,
+            model_iter: model[model_clip_top..model_clip_bot + 1].iter(),
+        }
+    }
+}