From b2a2c1a917ae31f95f7c675e05aa5632cd56a6f8 Mon Sep 17 00:00:00 2001
From: Glenn Watson <github@intuitionlibrary.com>
Date: Wed, 11 Oct 2017 15:30:40 +1000
Subject: [PATCH] If a stacking context is isolated, disable subpixel AA on it.

This is a workaround / hack for #1839, until we properly support
subpixel AA on transparent surfaces. It extends the set of
conditions that disable subpixel AA on a stacking context.

Fixes #1839.
---
 webrender/src/frame_builder.rs          |   2 +-
 webrender/src/tiling.rs                 |   8 ++++++++
 wrench/reftests/text/isolated-text.png  | Bin 0 -> 6737 bytes
 wrench/reftests/text/isolated-text.yaml |  14 ++++++++++++++
 wrench/reftests/text/reftest.list       |   2 ++
 wrench/src/yaml_helper.rs               |   3 +++
 6 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 wrench/reftests/text/isolated-text.png
 create mode 100644 wrench/reftests/text/isolated-text.yaml

diff --git a/webrender/src/frame_builder.rs b/webrender/src/frame_builder.rs
index b9a30de858..48e9a85161 100644
--- a/webrender/src/frame_builder.rs
+++ b/webrender/src/frame_builder.rs
@@ -1153,7 +1153,7 @@ impl FrameBuilder {
             //           we handle subpixel blending.
             if let Some(sc_index) = self.stacking_context_stack.last() {
                 let stacking_context = &self.stacking_context_store[sc_index.0];
-                if stacking_context.composite_ops.count() > 0 {
+                if !stacking_context.allow_subpixel_aa {
                     render_mode = FontRenderMode::Alpha;
                 }
             }
diff --git a/webrender/src/tiling.rs b/webrender/src/tiling.rs
index 0453951d07..2a1813493c 100644
--- a/webrender/src/tiling.rs
+++ b/webrender/src/tiling.rs
@@ -1601,6 +1601,11 @@ pub struct StackingContext {
 
     /// Current stacking context visibility of backface.
     pub is_backface_visible: bool,
+
+    /// Allow subpixel AA for text runs on this stacking context.
+    /// This is a temporary hack while we don't support subpixel AA
+    /// on transparent stacking contexts.
+    pub allow_subpixel_aa: bool,
 }
 
 impl StackingContext {
@@ -1618,6 +1623,8 @@ impl StackingContext {
             TransformStyle::Flat => ContextIsolation::None,
             TransformStyle::Preserve3D => ContextIsolation::Items,
         };
+        let allow_subpixel_aa = composite_ops.count() == 0 &&
+                                isolation == ContextIsolation::None;
         StackingContext {
             pipeline_id,
             reference_frame_offset,
@@ -1630,6 +1637,7 @@ impl StackingContext {
             is_pipeline_root,
             is_visible: false,
             is_backface_visible,
+            allow_subpixel_aa,
         }
     }
 
diff --git a/wrench/reftests/text/isolated-text.png b/wrench/reftests/text/isolated-text.png
new file mode 100644
index 0000000000000000000000000000000000000000..7b310e78dcb2ec25cfa7797615b58bbdfe19c72f
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diff --git a/wrench/reftests/text/isolated-text.yaml b/wrench/reftests/text/isolated-text.yaml
new file mode 100644
index 0000000000..897d410a84
--- /dev/null
+++ b/wrench/reftests/text/isolated-text.yaml
@@ -0,0 +1,14 @@
+root:
+  items:
+    - type: stacking-context
+      bounds: [0, 0, 1000, 100]
+      transform: perspective(1000)
+      items:
+      - type: stacking-context
+        bounds: [0, 0, 1000, 100]
+        transform-style: preserve-3d
+        items:
+          - text: "Cats making all the muffins knock over christmas tree"
+            origin: 20 30
+            size: 20
+            font: "FreeSans.ttf"
diff --git a/wrench/reftests/text/reftest.list b/wrench/reftests/text/reftest.list
index 10aa0f4ed0..9ad658a714 100644
--- a/wrench/reftests/text/reftest.list
+++ b/wrench/reftests/text/reftest.list
@@ -23,3 +23,5 @@ fuzzy(1,160) == shadow-grey.yaml shadow-grey-ref.yaml
 # enable when synthetic-italics implemented on mac
 platform(linux) != synthetic-italics.yaml synthetic-italics-ref.yaml
 options(disable-subpixel) == ahem.yaml ahem-ref.yaml
+platform(linux) == isolated-text.yaml isolated-text.png
+
diff --git a/wrench/src/yaml_helper.rs b/wrench/src/yaml_helper.rs
index 4db2b244a1..d6d1f87b66 100644
--- a/wrench/src/yaml_helper.rs
+++ b/wrench/src/yaml_helper.rs
@@ -332,6 +332,9 @@ impl YamlHelper for Yaml {
                         "rotate-y" if args.len() == 1 => {
                             make_rotation(transform_origin, args[0].parse().unwrap(), 0.0, 1.0, 0.0)
                         }
+                        "perspective" if args.len() == 1 => {
+                            LayoutTransform::create_perspective(args[0].parse().unwrap())
+                        }
                         _ => {
                             println!("unknown function {}", function);
                             break;