add helper to know when a colortype is always opaque

Now that surface creation is more picky about its imageinfo, we need to
allow clients to know when they should clean-up their alphatype (like
our own gm)

Bug: skia:
Change-Id: Ic110c75769e0154a8343d7e2160d3351f02cf48f
Reviewed-on: https://skia-review.googlesource.com/106320
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/gm/imagealphathreshold.cpp b/gm/imagealphathreshold.cpp
index 3783bfcb3a..4bdf6eb5a2 100644
--- a/gm/imagealphathreshold.cpp
+++ b/gm/imagealphathreshold.cpp
@@ -89,7 +89,7 @@ private:
 // Create a 'width' x 'height' SkSurface that matches the colorType of 'canvas' as
 // best we can
 static sk_sp<SkSurface> make_color_matching_surface(SkCanvas* canvas, int width, int height,
-                                                    SkAlphaType alphaType) {
+                                                    SkAlphaType at) {
 
     SkColorType ct = canvas->imageInfo().colorType();
     sk_sp<SkColorSpace> cs(canvas->imageInfo().refColorSpace());
@@ -98,9 +98,11 @@ static sk_sp<SkSurface> make_color_matching_surface(SkCanvas* canvas, int width,
         // For backends that aren't yet color-space aware we just fallback to N32.
         ct = kN32_SkColorType;
         cs = nullptr;
+    } else if (SkColorTypeIsAlwaysOpaque(ct)) {
+        at = kOpaque_SkAlphaType;
     }
 
-    SkImageInfo info = SkImageInfo::Make(width, height, ct, alphaType, std::move(cs));
+    SkImageInfo info = SkImageInfo::Make(width, height, ct, at, std::move(cs));
 
     return sk_tool_utils::makeSurface(canvas, info);
 }