Refactor: put each shape into its own file (#5564)

Much easier to navigate the code

crates/epaint/src/viewport.rs

@@ -0,0 +1,54 @@
+use crate::Rect;
+
+/// Size of the viewport in whole, physical pixels.
+pub struct ViewportInPixels {
+    /// Physical pixel offset for left side of the viewport.
+    pub left_px: i32,
+
+    /// Physical pixel offset for top side of the viewport.
+    pub top_px: i32,
+
+    /// Physical pixel offset for bottom side of the viewport.
+    ///
+    /// This is what `glViewport`, `glScissor` etc expects for the y axis.
+    pub from_bottom_px: i32,
+
+    /// Viewport width in physical pixels.
+    pub width_px: i32,
+
+    /// Viewport height in physical pixels.
+    pub height_px: i32,
+}
+
+impl ViewportInPixels {
+    /// Convert from ui points.
+    pub fn from_points(rect: &Rect, pixels_per_point: f32, screen_size_px: [u32; 2]) -> Self {
+        // Fractional pixel values for viewports are generally valid, but may cause sampling issues
+        // and rounding errors might cause us to get out of bounds.
+
+        // Round:
+        let left_px = (pixels_per_point * rect.min.x).round() as i32; // inclusive
+        let top_px = (pixels_per_point * rect.min.y).round() as i32; // inclusive
+        let right_px = (pixels_per_point * rect.max.x).round() as i32; // exclusive
+        let bottom_px = (pixels_per_point * rect.max.y).round() as i32; // exclusive
+
+        // Clamp to screen:
+        let screen_width = screen_size_px[0] as i32;
+        let screen_height = screen_size_px[1] as i32;
+        let left_px = left_px.clamp(0, screen_width);
+        let right_px = right_px.clamp(left_px, screen_width);
+        let top_px = top_px.clamp(0, screen_height);
+        let bottom_px = bottom_px.clamp(top_px, screen_height);
+
+        let width_px = right_px - left_px;
+        let height_px = bottom_px - top_px;
+
+        Self {
+            left_px,
+            top_px,
+            from_bottom_px: screen_height - height_px - top_px,
+            width_px,
+            height_px,
+        }
+    }
+}