Fix T-junctions in layers' generated meshes
bug:4128442
Currently we fix T-junctions for hardware layers, and for
Canvas.saveLayer if the transform isn't rectAsRect. Ideally, hardware
layers should lazily re-generate T-junction free geometry if the
transform becomes non-rectAsRect
Depends on frameworks/native change:
https://googleplex-android-review.googlesource.com/#/c/277668/
which adds Region::createTJunctionFreeRegion()
Change-Id: Ice75b4a1a4459ff835059ea81d70f7d1563fd96d
diff --git a/libs/hwui/LayerRenderer.cpp b/libs/hwui/LayerRenderer.cpp
index bc660cd..14c7c39 100644
--- a/libs/hwui/LayerRenderer.cpp
+++ b/libs/hwui/LayerRenderer.cpp
@@ -123,13 +123,9 @@
return &mLayer->region;
}
-// TODO: This implementation is flawed and can generate T-junctions
-// in the mesh, which will in turn produce cracks when the
-// mesh is rotated/skewed. The easiest way to fix this would
-// be, for each row, to add new vertices shared with the previous
-// row when the two rows share an edge.
-// In practice, T-junctions do not appear often so this has yet
-// to be fixed.
+// TODO: This implementation uses a very simple approach to fixing T-junctions which keeps the
+// results as rectangles, and is thus not necessarily efficient in the geometry
+// produced. Eventually, it may be better to develop triangle-based mechanism.
void LayerRenderer::generateMesh() {
if (mLayer->region.isRect() || mLayer->region.isEmpty()) {
if (mLayer->mesh) {
@@ -145,8 +141,14 @@
return;
}
+ // avoid T-junctions as they cause artifacts in between the resultant
+ // geometry when complex transforms occur.
+ // TODO: generate the safeRegion only if necessary based on drawing transform (see
+ // OpenGLRenderer::composeLayerRegion())
+ Region safeRegion = Region::createTJunctionFreeRegion(mLayer->region);
+
size_t count;
- const android::Rect* rects = mLayer->region.getArray(&count);
+ const android::Rect* rects = safeRegion.getArray(&count);
GLsizei elementCount = count * 6;