Snap borders with odd pixel width to pixel boundaries.

Add debug bounding boxes for text boxes (RUST_LOG=servo::layout::box)
and all boxes (RUST_LOG=servo::gfx::display_list).

src/servo/gfx/display_list.rs

@@ -1,5 +1,6 @@
 use azure::azure_hl::DrawTarget;
-use gfx::geometry::*;
+use au = gfx::geometry;
+use au::Au;
 use geom::rect::Rect;
 use image::base::Image;
 use render_context::RenderContext;
@@ -53,6 +54,10 @@ impl DisplayItem {
             Image(_, ref img) => ctx.draw_image(self.d().bounds, clone_arc(img)),
             Border(_, width, r, g, b) => ctx.draw_border(&self.d().bounds, width, r, g, b),
         }
+
+        debug!("%?", {
+        ctx.draw_border(&self.d().bounds, au::from_px(1), 150, 150, 150);
+        () });
     }
 
     static pure fn new_SolidColor(bounds: &Rect<Au>, r: u8, g: u8, b: u8) -> DisplayItem {
@@ -81,14 +86,16 @@ trait DisplayListMethods {
 
 impl DisplayList : DisplayListMethods {
     fn append_item(item: ~DisplayItem) {
-        debug!("Adding display item %u: %?", self.len(), item);
+        // FIXME(Issue #150): crashes
+        //debug!("Adding display item %u: %?", self.len(), item);
         self.push(move item);
     }
 
     fn draw_into_context(ctx: &RenderContext) {
         debug!("beginning display list");
         for self.each |item| {
-            debug!("drawing %?", *item);
+            // FIXME(Issue #150): crashes
+            //debug!("drawing %?", *item);
             item.draw_into_context(ctx);
         }
         debug!("ending display list");

src/servo/gfx/geometry.rs

@@ -70,6 +70,10 @@ pub pure fn to_px(au: Au) -> int {
     (*au / 60) as int
 }
 
+pub pure fn to_frac_px(au: Au) -> float {
+    (*au as float) / 60f
+}
+
 // assumes 72 points per inch, and 96 px per inch
 pub pure fn from_pt(f: float) -> Au {
     from_px((f / 72f * 96f) as int)

src/servo/gfx/render_context.rs

@@ -38,14 +38,20 @@ impl RenderContext  {
     }
 
     pub fn draw_border(&self, bounds: &Rect<Au>, width: Au, r: u8, g: u8, b: u8) {
-        let rect = bounds.to_azure_rect();
         let color = Color(r.to_float() as AzFloat,
                           g.to_float() as AzFloat,
                           b.to_float() as AzFloat,
                           1f as AzFloat);
         let pattern = ColorPattern(color);
         let stroke_fields = 2; // CAP_SQUARE
-        let stroke_opts = StrokeOptions(au::to_px(width) as AzFloat, 10 as AzFloat, stroke_fields);
+        let width_px = au::to_px(width);
+        let rect = if width_px % 2 == 0 {
+            bounds.to_azure_rect()
+        } else {
+            bounds.to_azure_snapped_rect()
+        };
+            
+        let stroke_opts = StrokeOptions(width_px as AzFloat, 10 as AzFloat, stroke_fields);
         let draw_opts = DrawOptions(1 as AzFloat, 0 as uint16_t);
 
         self.canvas.draw_target.stroke_rect(&rect, &pattern, &stroke_opts, &draw_opts);
@@ -162,6 +168,7 @@ impl u8 : to_float {
 
 trait ToAzureRect {
     fn to_azure_rect() -> Rect<AzFloat>;
+    fn to_azure_snapped_rect() -> Rect<AzFloat>;
 }
 
 impl Rect<Au> : ToAzureRect {
@@ -169,6 +176,11 @@ impl Rect<Au> : ToAzureRect {
         Rect(Point2D(au::to_px(self.origin.x) as AzFloat, au::to_px(self.origin.y) as AzFloat),
              Size2D(au::to_px(self.size.width) as AzFloat, au::to_px(self.size.height) as AzFloat))
     }
+
+    fn to_azure_snapped_rect() -> Rect<AzFloat> {
+        Rect(Point2D(au::to_px(self.origin.x) as AzFloat + 0.5f as AzFloat, au::to_px(self.origin.y) as AzFloat + 0.5f as AzFloat),
+             Size2D(au::to_px(self.size.width) as AzFloat, au::to_px(self.size.height) as AzFloat))
+    }
 }
 
 #[cfg(target_os = "linux")]

src/servo/layout/box.rs

@@ -420,7 +420,11 @@ impl RenderBox : RenderBoxMethods {
             TextBox(_,d) => {
                 list.append_item(~DisplayItem::new_Text(&abs_box_bounds, 
                                                         ~d.run.serialize(builder.ctx.font_cache),
-                                                        d.range))
+                                                        d.range));
+                // debug frames for text box bounds
+                debug!("%?", { 
+                    list.append_item(~DisplayItem::new_Border(&abs_box_bounds, au::from_px(1), 0, 0, 200))
+                ; ()});
             },
             // TODO: items for background, border, outline
             GenericBox(_) => {