Add proper aliased support for SDF text

Previously, when asked to render aliased text with distance fields,
we would get the aliased glyph from the cache and then try to
anti-alias the edge. This change instead grabs the anti-aliased glyph,
then deliberately aliases the edge.

Bug: chromium:707979
Change-Id: I05766af17d7ae58bca27aaffd9e08e5c586e789c
Reviewed-on: https://skia-review.googlesource.com/21728
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/src/gpu/effects/GrDistanceFieldGeoProc.cpp b/src/gpu/effects/GrDistanceFieldGeoProc.cpp
index f0f4ec4fa3..c8dd4ebd77 100644
--- a/src/gpu/effects/GrDistanceFieldGeoProc.cpp
+++ b/src/gpu/effects/GrDistanceFieldGeoProc.cpp
@@ -77,6 +77,8 @@ public:
         bool isSimilarity = SkToBool(dfTexEffect.getFlags() & kSimilarity_DistanceFieldEffectFlag);
         bool isGammaCorrect =
             SkToBool(dfTexEffect.getFlags() & kGammaCorrect_DistanceFieldEffectFlag);
+        bool isAliased =
+            SkToBool(dfTexEffect.getFlags() & kAliased_DistanceFieldEffectFlag);
         varyingHandler->addVarying("TextureCoords", &uv, kHigh_GrSLPrecision);
         vertBuilder->codeAppendf("%s = %s;", uv.vsOut(), dfTexEffect.inTextureCoords()->fName);
 
@@ -158,10 +160,12 @@ public:
             fragBuilder->codeAppend("afwidth = " SK_DistanceFieldAAFactor "*length(grad);");
         }
 
-        // The smoothstep falloff compensates for the non-linear sRGB response curve. If we are
-        // doing gamma-correct rendering (to an sRGB or F16 buffer), then we actually want distance
-        // mapped linearly to coverage, so use a linear step:
-        if (isGammaCorrect) {
+        if (isAliased) {
+            fragBuilder->codeAppend("float val = distance > 0 ? 1.0 : 0.0;");
+        } else if (isGammaCorrect) {
+            // The smoothstep falloff compensates for the non-linear sRGB response curve. If we are
+            // doing gamma-correct rendering (to an sRGB or F16 buffer), then we actually want
+            // distance mapped linearly to coverage, so use a linear step:
             fragBuilder->codeAppend(
                 "float val = clamp((distance + afwidth) / (2.0 * afwidth), 0.0, 1.0);");
         } else {