handle halfway case in scan converter

Scan edges that start at exactly -0.5 aren't trimmed by
clipping or by rounding, triggering a debug assert.

One way to fix this is to round the top and left
down instead of up.

Also, move the path initialization of gm/composeshader.cpp
to make debugging other path problems easier.

R=reed@google.com
BUG=skia:2715
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1544873002

Review URL: https://codereview.chromium.org/1544873002

1 files changed, 9 insertions, 1 deletions

diff --git a/gm/composeshader.cpp b/gm/composeshader.cpp
index e012bbb285..b2be9ba28e 100644
--- a/gm/composeshader.cpp
+++ b/gm/composeshader.cpp
@@ -162,7 +162,14 @@ static SkShader* make_linear_gradient_shader(int length) {
 
 class ComposeShaderBitmapGM : public skiagm::GM {
 public:
-    ComposeShaderBitmapGM() {
+    ComposeShaderBitmapGM()
+        : fColorBitmapShader(nullptr)
+        , fAlpha8BitmapShader(nullptr)
+        , fLinearGradientShader(nullptr)
+    {
+    }
+
+    void onOnceBeforeDraw() override {
         draw_color_bm(&fColorBitmap, squareLength);
         draw_alpha8_bm(&fAlpha8Bitmap, squareLength);
         SkMatrix s;
@@ -173,6 +180,7 @@ public:
                                                      SkShader::kRepeat_TileMode, &s);
         fLinearGradientShader = make_linear_gradient_shader(squareLength);
     }
+
     ~ComposeShaderBitmapGM() {
         SkSafeUnref(fColorBitmapShader);
         SkSafeUnref(fAlpha8BitmapShader);