Auto merge of #540 - samuknet:home-end-key-scroll2, r=glennw

Implement Home end key scroll

Addressing issue servo/servo#13082.
Supporting servo/servo#14141.

* Adds `ScrollLocation` type in `webrender_traits`.
* Refactor api to use new `ScrollLocation`
* Implement home/end scrolling in `webrender/src/frame.rs` `fn scroll(...)` using new `ScrollLocation` struct passed in.

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Author: bors-servo

webrender/src/frame.rs

@@ -19,7 +19,7 @@ use tiling::{AuxiliaryListsMap, FrameBuilder, FrameBuilderConfig, LayerMap, Prim
 use util::MatrixHelpers;
 use webrender_traits::{AuxiliaryLists, PipelineId, Epoch, ScrollPolicy, ScrollLayerId};
 use webrender_traits::{ClipRegion, ColorF, DisplayItem, StackingContext, FilterOp, MixBlendMode};
-use webrender_traits::{ScrollEventPhase, ScrollLayerInfo, SpecificDisplayItem, ScrollLayerState};
+use webrender_traits::{ScrollEventPhase, ScrollLayerInfo, ScrollLocation, SpecificDisplayItem, ScrollLayerState};
 use webrender_traits::{LayerRect, LayerPoint, LayerSize};
 use webrender_traits::{ServoScrollRootId, ScrollLayerRect, as_scroll_parent_rect, ScrollLayerPixel};
 use webrender_traits::WorldPoint4D;
@@ -329,7 +329,7 @@ impl Frame {
 
     /// Returns true if any layers actually changed position or false otherwise.
     pub fn scroll(&mut self,
-                  mut delta: Point2D<f32>,
+                  scroll_location: ScrollLocation,
                   cursor: Point2D<f32>,
                   phase: ScrollEventPhase)
                   -> bool {
@@ -364,6 +364,33 @@ impl Frame {
                 continue;
             }
 
+            let mut delta = match scroll_location {
+                ScrollLocation::Delta(delta) => delta,
+                ScrollLocation::Start => {
+                    if layer.scrolling.offset.y.round() <= 0.0 {
+                        // Nothing to do on this layer.
+                        continue;
+                    }
+
+                    layer.scrolling.offset.y = 0.0;
+                    scrolled_a_layer = true;
+                    continue;
+                },
+                ScrollLocation::End => {
+                    let end_pos = layer.local_viewport_rect.size.height
+                                  - layer.content_size.height;
+
+                    if layer.scrolling.offset.y.round() >= end_pos {
+                        // Nothing to do on this layer.
+                        continue;
+                    }
+                
+                    layer.scrolling.offset.y = end_pos;
+                    scrolled_a_layer = true;
+                    continue;
+                }
+            };
+
             let overscroll_amount = layer.overscroll_amount();
             let overscrolling = CAN_OVERSCROLL && (overscroll_amount.width != 0.0 ||
                                                    overscroll_amount.height != 0.0);

webrender_traits/src/api.rs

@@ -9,7 +9,7 @@ use offscreen_gl_context::{GLContextAttributes, GLLimits};
 use std::cell::Cell;
 use {ApiMsg, ColorF, DisplayListBuilder, Epoch};
 use {FontKey, IdNamespace, ImageFormat, ImageKey, NativeFontHandle, PipelineId};
-use {RenderApiSender, ResourceId, ScrollEventPhase, ScrollLayerState, ServoScrollRootId};
+use {RenderApiSender, ResourceId, ScrollEventPhase, ScrollLayerState, ScrollLocation, ServoScrollRootId};
 use {GlyphKey, GlyphDimensions, ImageData, WebGLContextId, WebGLCommand};
 
 impl RenderApiSender {
@@ -188,8 +188,8 @@ impl RenderApi {
     ///
     /// Webrender looks for the layer closest to the user
     /// which has `ScrollPolicy::Scrollable` set.
-    pub fn scroll(&self, delta: Point2D<f32>, cursor: Point2D<f32>, phase: ScrollEventPhase) {
-        let msg = ApiMsg::Scroll(delta, cursor, phase);
+    pub fn scroll(&self, scroll_location: ScrollLocation, cursor: Point2D<f32>, phase: ScrollEventPhase) {
+        let msg = ApiMsg::Scroll(scroll_location, cursor, phase);
         self.api_sender.send(msg).unwrap();
     }
 

webrender_traits/src/types.rs

@@ -48,7 +48,7 @@ pub enum ApiMsg {
                        BuiltDisplayListDescriptor,
                        AuxiliaryListsDescriptor),
     SetRootPipeline(PipelineId),
-    Scroll(Point2D<f32>, Point2D<f32>, ScrollEventPhase),
+    Scroll(ScrollLocation, Point2D<f32>, ScrollEventPhase),
     ScrollLayersWithScrollId(Point2D<f32>, PipelineId, ServoScrollRootId),
     TickScrollingBounce,
     TranslatePointToLayerSpace(Point2D<f32>, MsgSender<(Point2D<f32>, PipelineId)>),
@@ -491,6 +491,16 @@ pub enum ScrollPolicy {
     Fixed,
 }
 
+#[derive(Clone, Copy, Debug, Deserialize, Serialize)]
+pub enum ScrollLocation {
+    /// Scroll by a certain amount.
+    Delta(Point2D<f32>), 
+    /// Scroll to very top of element.
+    Start,
+    /// Scroll to very bottom of element. 
+    End 
+}
+
 #[derive(Clone, Copy, Debug, Deserialize, Eq, Hash, PartialEq, Serialize)]
 pub struct ServoScrollRootId(pub usize);