Fix various hw-accelerated line/point bugs

All accelerated lines are now rendered as quads. Hairlines used to
be rendered as GL_LINES, but these lines don't render the same as our
non-accelerated lines, so we're using quads for everything. Also, fixed
a bug in the way that we were offsetting quads (and not offseting points)
to ensure that our lines/points actuall start on the same pixels as
Skia's.

Change-Id: I51b923cc08a9858444c430ba07bc8aa0c83cbe6a

1 files changed, 8 insertions, 1 deletions

diff --git a/libs/hwui/Program.cpp b/libs/hwui/Program.cpp
index 2187f24e2c83..972dd87a5d71 100644
--- a/libs/hwui/Program.cpp
+++ b/libs/hwui/Program.cpp
@@ -124,8 +124,15 @@ GLuint Program::buildShader(const char* source, GLenum type) {
 }
 
 void Program::set(const mat4& projectionMatrix, const mat4& modelViewMatrix,
-        const mat4& transformMatrix) {
+        const mat4& transformMatrix, bool offset) {
     mat4 t(projectionMatrix);
+    if (offset) {
+        // offset screenspace xy by an amount that compensates for typical precision issues
+        // in GPU hardware that tends to paint hor/vert lines in pixels shifted up and to the left.
+        // This offset value is based on an assumption that some hardware may use as little
+        // as 12.4 precision, so we offset by slightly more than 1/16.
+        t.translate(.375, .375, 0);
+    }
     t.multiply(transformMatrix);
     t.multiply(modelViewMatrix);