specialize bicubic filtering for scale-only

src/core/SkBitmapProcBicubic.cpp

Index: src/core/SkBitmapProcBicubic.cpp
diff --git a/src/core/SkBitmapProcBicubic.cpp b/src/core/SkBitmapProcBicubic.cpp
index 1c415fdadfa6937c2a4335710cc50c235eae5153..1616808484c265be13bd7dd362f7f3cb7cfa71e9 100644
--- a/src/core/SkBitmapProcBicubic.cpp
+++ b/src/core/SkBitmapProcBicubic.cpp
@@ -35,22 +35,49 @@ static float poly_eval(const float cc[4], float t) {
     return cc[0] + t * (cc[1] + t * (cc[2] + t * cc[3]));
 }
 
-static void build_coeff4(SkFixed dst[4], const float src[16], float t) {
-    dst[0] = SkFloatToFixed(poly_eval(&src[ 0], t));
-    dst[1] = SkFloatToFixed(poly_eval(&src[ 4], t));
-    dst[2] = SkFloatToFixed(poly_eval(&src[ 8], t));
-    dst[3] = SkFloatToFixed(poly_eval(&src[12], t));
-}
-
-static void bicubicFilter(const SkBitmapProcState& s, int x, int y,
-                          SkPMColor* SK_RESTRICT colors, int count) {
-
+static void build_coeff4(SkFixed dst[4], float t) {
     static const SkScalar coefficients[16] = {
         DS( 1.0 / 18.0), DS(-9.0 / 18.0), DS( 15.0 / 18.0), DS( -7.0 / 18.0),
         DS(16.0 / 18.0), DS( 0.0 / 18.0), DS(-36.0 / 18.0), DS( 21.0 / 18.0),
         DS( 1.0 / 18.0), DS( 9.0 / 18.0), DS( 27.0 / 18.0), DS(-21.0 / 18.0),
         DS( 0.0 / 18.0), DS( 0.0 / 18.0), DS( -6.0 / 18.0), DS(  7.0 / 18.0),
     };
+    
+    dst[0] = SkFloatToFixed(poly_eval(&coefficients[ 0], t));
+    dst[1] = SkFloatToFixed(poly_eval(&coefficients[ 4], t));
+    dst[2] = SkFloatToFixed(poly_eval(&coefficients[ 8], t));
+    dst[3] = SkFloatToFixed(poly_eval(&coefficients[12], t));
+}
+
+static SkPMColor doBicubicFilter(const SkBitmap *bm, SkFixed coeffX[4], SkFixed coeffY[4],
+                            int x0, int x1, int x2, int x3,
+                            int y0, int y1, int y2, int y3 )
+{
+    SkPMColor s00 = *bm->getAddr32(x0, y0);
+    SkPMColor s10 = *bm->getAddr32(x1, y0);
+    SkPMColor s20 = *bm->getAddr32(x2, y0);
+    SkPMColor s30 = *bm->getAddr32(x3, y0);
+    SkPMColor s0 = cubicBlend(coeffX, s00, s10, s20, s30);
+    SkPMColor s01 = *bm->getAddr32(x0, y1);
+    SkPMColor s11 = *bm->getAddr32(x1, y1);
+    SkPMColor s21 = *bm->getAddr32(x2, y1);
+    SkPMColor s31 = *bm->getAddr32(x3, y1);
+    SkPMColor s1 = cubicBlend(coeffX, s01, s11, s21, s31);
+    SkPMColor s02 = *bm->getAddr32(x0, y2);
+    SkPMColor s12 = *bm->getAddr32(x1, y2);
+    SkPMColor s22 = *bm->getAddr32(x2, y2);
+    SkPMColor s32 = *bm->getAddr32(x3, y2);
+    SkPMColor s2 = cubicBlend(coeffX, s02, s12, s22, s32);
+    SkPMColor s03 = *bm->getAddr32(x0, y3);
+    SkPMColor s13 = *bm->getAddr32(x1, y3);
+    SkPMColor s23 = *bm->getAddr32(x2, y3);
+    SkPMColor s33 = *bm->getAddr32(x3, y3);
+    SkPMColor s3 = cubicBlend(coeffX, s03, s13, s23, s33);
+    return cubicBlend(coeffY, s0, s1, s2, s3);
+}
+
+static void bicubicFilter(const SkBitmapProcState& s, int x, int y,
+                          SkPMColor* SK_RESTRICT colors, int count) {
 
     const int maxX = s.fBitmap->width() - 1;
     const int maxY = s.fBitmap->height() - 1;
@@ -65,8 +92,8 @@ static void bicubicFilter(const SkBitmapProcState& s, int x, int y,
         SkScalar fracty = srcPt.fY - SkScalarFloorToScalar(srcPt.fY);
 
         SkFixed coeffX[4], coeffY[4];
-        build_coeff4(coeffX, coefficients, fractx);
-        build_coeff4(coeffY, coefficients, fracty);
+        build_coeff4(coeffX, fractx);
+        build_coeff4(coeffY, fracty);
 
         int sx = SkScalarFloorToInt(srcPt.fX);
         int sy = SkScalarFloorToInt(srcPt.fY);
@@ -80,28 +107,47 @@ static void bicubicFilter(const SkBitmapProcState& s, int x, int y,
         int y1 = SkClampMax(sy    , maxY);
         int y2 = SkClampMax(sy + 1, maxY);
         int y3 = SkClampMax(sy + 2, maxY);
+        
+        *colors++ = doBicubicFilter( s.fBitmap, coeffX, coeffY, x0, x1, x2, x3, y0, y1, y2, y3 );
+
+        x++;
+    }
+}
+
+static void bicubicFilter_ScaleOnly(const SkBitmapProcState &s, int x, int y,
+                                    SkPMColor *SK_RESTRICT colors, int count) {
+    const int maxX = s.fBitmap->width() - 1;
+    const int maxY = s.fBitmap->height() - 1;
+
+    SkPoint srcPt;
+    s.fInvProc(*s.fInvMatrix, SkIntToScalar(x), SkIntToScalar(y), &srcPt);
+    srcPt.fY -= SK_ScalarHalf;
+    SkScalar fracty = srcPt.fY - SkScalarFloorToScalar(srcPt.fY);
+    SkFixed coeffX[4], coeffY[4];
+    build_coeff4(coeffY, fracty);
+    int sy = SkScalarFloorToInt(srcPt.fY);
+    int y0 = SkClampMax(sy - 1, maxY);
+    int y1 = SkClampMax(sy    , maxY);
+    int y2 = SkClampMax(sy + 1, maxY);
+    int y3 = SkClampMax(sy + 2, maxY);
+
+    while (count-- > 0) {
+        s.fInvProc(*s.fInvMatrix, SkIntToScalar(x), SkIntToScalar(y), &srcPt);
+        srcPt.fX -= SK_ScalarHalf;
+        SkScalar fractx = srcPt.fX - SkScalarFloorToScalar(srcPt.fX);
+
+        build_coeff4(coeffX, fractx);
+
+        int sx = SkScalarFloorToInt(srcPt.fX);
+
+        // Here is where we can support other tile modes (e.g. repeat or mirror)
+        int x0 = SkClampMax(sx - 1, maxX);
+        int x1 = SkClampMax(sx    , maxX);
+        int x2 = SkClampMax(sx + 1, maxX);
+        int x3 = SkClampMax(sx + 2, maxX);
+
+        *colors++ = doBicubicFilter( s.fBitmap, coeffX, coeffY, x0, x1, x2, x3, y0, y1, y2, y3 );
 
-        SkPMColor s00 = *s.fBitmap->getAddr32(x0, y0);
-        SkPMColor s10 = *s.fBitmap->getAddr32(x1, y0);
-        SkPMColor s20 = *s.fBitmap->getAddr32(x2, y0);
-        SkPMColor s30 = *s.fBitmap->getAddr32(x3, y0);
-        SkPMColor s0 = cubicBlend(coeffX, s00, s10, s20, s30);
-        SkPMColor s01 = *s.fBitmap->getAddr32(x0, y1);
-        SkPMColor s11 = *s.fBitmap->getAddr32(x1, y1);
-        SkPMColor s21 = *s.fBitmap->getAddr32(x2, y1);
-        SkPMColor s31 = *s.fBitmap->getAddr32(x3, y1);
-        SkPMColor s1 = cubicBlend(coeffX, s01, s11, s21, s31);
-        SkPMColor s02 = *s.fBitmap->getAddr32(x0, y2);
-        SkPMColor s12 = *s.fBitmap->getAddr32(x1, y2);
-        SkPMColor s22 = *s.fBitmap->getAddr32(x2, y2);
-        SkPMColor s32 = *s.fBitmap->getAddr32(x3, y2);
-        SkPMColor s2 = cubicBlend(coeffX, s02, s12, s22, s32);
-        SkPMColor s03 = *s.fBitmap->getAddr32(x0, y3);
-        SkPMColor s13 = *s.fBitmap->getAddr32(x1, y3);
-        SkPMColor s23 = *s.fBitmap->getAddr32(x2, y3);
-        SkPMColor s33 = *s.fBitmap->getAddr32(x3, y3);
-        SkPMColor s3 = cubicBlend(coeffX, s03, s13, s23, s33);
-        *colors++ = cubicBlend(coeffY, s0, s1, s2, s3);
         x++;
     }
 }
@@ -130,6 +176,12 @@ SkBitmapProcState::chooseBicubicFilterProc(const SkPaint& paint) {
     if (0xFF != paint.getAlpha()) {
         return NULL;
     }
-
-    return bicubicFilter;
+    
+    if (fInvType & SkMatrix::kAffine_Mask) {
+        return bicubicFilter;
+    } else if (fInvType & SkMatrix::kScale_Mask) {
+        return bicubicFilter_ScaleOnly;
+    } else {
+        return NULL;
+    }
 }