Planar ramp() for S32 linear gradients

src/effects/gradients/Sk4fLinearGradient.cpp

Index: src/effects/gradients/Sk4fLinearGradient.cpp
diff --git a/src/effects/gradients/Sk4fLinearGradient.cpp b/src/effects/gradients/Sk4fLinearGradient.cpp
index f4bb4a7d1829d67598855354ead50a3b85dfae00..4ea025d0d2781b995ee03e42fcc80bfdcd0d83ad 100644
--- a/src/effects/gradients/Sk4fLinearGradient.cpp
+++ b/src/effects/gradients/Sk4fLinearGradient.cpp
@@ -6,6 +6,7 @@
  */
 
 #include "Sk4fLinearGradient.h"
+#include "Sk4x4f.h"
 #include "SkXfermode.h"
 
 namespace {
@@ -42,6 +43,41 @@ void ramp(const Sk4f& c, const Sk4f& dc, typename DstTraits<dstType, premul>::Ty
     }
 }
 
+// Planar version of ramp (S32 no-premul only).
+template<>
+void ramp<DstType::S32, ApplyPremul::False>(const Sk4f& c, const Sk4f& dc, SkPMColor dst[], int n) {
+    SkASSERT(n > 0);
+
+    const Sk4f    dc4 = dc * 4;
+    const Sk4x4f dc4x = { Sk4f(dc4[0]), Sk4f(dc4[1]), Sk4f(dc4[2]), Sk4f(dc4[3]) };
+    Sk4x4f        c4x = Sk4x4f::Transpose(c, c + dc, c + dc * 2, c + dc * 3);
+
+    while (n >= 4) {
+        const Sk4x4f cx4s32 = { c4x.r.sqrt(), c4x.g.sqrt(), c4x.b.sqrt(), c4x.a };
+        cx4s32.transpose((uint8_t*)dst);
+
+        c4x.r += dc4x.r;
+        c4x.g += dc4x.g;
+        c4x.b += dc4x.b;
+        c4x.a += dc4x.a;
+
+        dst += 4;
+        n   -= 4;
+    }
+
+    if (n & 2) {
+        DstTraits<DstType::S32, ApplyPremul::False>
+            ::store(Sk4f(c4x.r[0], c4x.g[0], c4x.b[0], c4x.a[0]), dst++);
+        DstTraits<DstType::S32, ApplyPremul::False>
+            ::store(Sk4f(c4x.r[1], c4x.g[1], c4x.b[1], c4x.a[1]), dst++);
+    }
+
+    if (n & 1) {
+        DstTraits<DstType::S32, ApplyPremul::False>
+            ::store(Sk4f(c4x.r[n & 2], c4x.g[n & 2], c4x.b[n & 2], c4x.a[n & 2]), dst);

[mtklein, 2016/03/23 19:05:27]

Wait, walk me through this one again?

[mtklein, 2016/03/23 19:12:57]

ok, cute!

+    }
+}
+
 template<SkShader::TileMode>
 SkScalar pinFx(SkScalar);