Fix tiled perlin noise.

It turns out that the perlin implementation we inherited from WebKit
does not actually generate tileable noise (see Chromium bug
http://crbug.com/383495).

The main problem is that when generating coordinates for gradient
interpolation, it was attempting to wrap both x and (x + 1)
simultaneously at the tile boundary (that is, either both or neither
are wrapped). This obviously won't work, since along the tile seams,
(x + 1) should be wrapped, but x should not. The same is true in y.

This patch fixes both the CPU and GPU paths, renames some variables to
more closely match the spec, and modifies the perlin noise GM to
actually test tiling. (Note that the clipping the GM was doing was
removed, since it's superfluous: it used to be necessary for image
filters, but isn't anymore, and this isn't an image filter GM anyway.)

R=sugoi@google.com, sugoi
TBR=senorblanco

Author: senorblanco@chromium.org

Review URL: https://codereview.chromium.org/332523006

1 files changed, 43 insertions, 34 deletions

diff --git a/src/effects/SkPerlinNoiseShader.cpp b/src/effects/SkPerlinNoiseShader.cpp
index bc24061d28..c230c2d648 100644
--- a/src/effects/SkPerlinNoiseShader.cpp
+++ b/src/effects/SkPerlinNoiseShader.cpp
@@ -39,9 +39,6 @@ inline int checkNoise(int noiseValue, int limitValue, int newValue) {
     if (noiseValue >= limitValue) {
         noiseValue -= newValue;
     }
-    if (noiseValue >= limitValue - 1) {
-        noiseValue -= newValue - 1;
-    }
     return noiseValue;
 }
 
@@ -320,12 +317,14 @@ SkScalar SkPerlinNoiseShader::PerlinNoiseShaderContext::noise2D(
         const StitchData& stitchData, const SkPoint& noiseVector) const {
     struct Noise {
         int noisePositionIntegerValue;
+        int nextNoisePositionIntegerValue;
         SkScalar noisePositionFractionValue;
         Noise(SkScalar component)
         {
             SkScalar position = component + kPerlinNoise;
             noisePositionIntegerValue = SkScalarFloorToInt(position);
             noisePositionFractionValue = position - SkIntToScalar(noisePositionIntegerValue);
+            nextNoisePositionIntegerValue = noisePositionIntegerValue + 1;
         }
     };
     Noise noiseX(noiseVector.x());
@@ -338,28 +337,36 @@ SkScalar SkPerlinNoiseShader::PerlinNoiseShaderContext::noise2D(
             checkNoise(noiseX.noisePositionIntegerValue, stitchData.fWrapX, stitchData.fWidth);
         noiseY.noisePositionIntegerValue =
             checkNoise(noiseY.noisePositionIntegerValue, stitchData.fWrapY, stitchData.fHeight);
+        noiseX.nextNoisePositionIntegerValue =
+            checkNoise(noiseX.nextNoisePositionIntegerValue, stitchData.fWrapX, stitchData.fWidth);
+        noiseY.nextNoisePositionIntegerValue =
+            checkNoise(noiseY.nextNoisePositionIntegerValue, stitchData.fWrapY, stitchData.fHeight);
     }
     noiseX.noisePositionIntegerValue &= kBlockMask;
     noiseY.noisePositionIntegerValue &= kBlockMask;
-    int latticeIndex =
-        paintingData.fLatticeSelector[noiseX.noisePositionIntegerValue] +
-        noiseY.noisePositionIntegerValue;
-    int nextLatticeIndex =
-        paintingData.fLatticeSelector[(noiseX.noisePositionIntegerValue + 1) & kBlockMask] +
-        noiseY.noisePositionIntegerValue;
+    noiseX.nextNoisePositionIntegerValue &= kBlockMask;
+    noiseY.nextNoisePositionIntegerValue &= kBlockMask;
+    int i =
+        paintingData.fLatticeSelector[noiseX.noisePositionIntegerValue];
+    int j =
+        paintingData.fLatticeSelector[noiseX.nextNoisePositionIntegerValue];
+    int b00 = (i + noiseY.noisePositionIntegerValue) & kBlockMask;
+    int b10 = (j + noiseY.noisePositionIntegerValue) & kBlockMask;
+    int b01 = (i + noiseY.nextNoisePositionIntegerValue) & kBlockMask;
+    int b11 = (j + noiseY.nextNoisePositionIntegerValue) & kBlockMask;
     SkScalar sx = smoothCurve(noiseX.noisePositionFractionValue);
     SkScalar sy = smoothCurve(noiseY.noisePositionFractionValue);
     // This is taken 1:1 from SVG spec: http://www.w3.org/TR/SVG11/filters.html#feTurbulenceElement
     SkPoint fractionValue = SkPoint::Make(noiseX.noisePositionFractionValue,
                                           noiseY.noisePositionFractionValue); // Offset (0,0)
-    u = paintingData.fGradient[channel][latticeIndex & kBlockMask].dot(fractionValue);
+    u = paintingData.fGradient[channel][b00].dot(fractionValue);
     fractionValue.fX -= SK_Scalar1; // Offset (-1,0)
-    v = paintingData.fGradient[channel][nextLatticeIndex & kBlockMask].dot(fractionValue);
+    v = paintingData.fGradient[channel][b10].dot(fractionValue);
     SkScalar a = SkScalarInterp(u, v, sx);
     fractionValue.fY -= SK_Scalar1; // Offset (-1,-1)
-    v = paintingData.fGradient[channel][(nextLatticeIndex + 1) & kBlockMask].dot(fractionValue);
+    v = paintingData.fGradient[channel][b11].dot(fractionValue);
     fractionValue.fX = noiseX.noisePositionFractionValue; // Offset (0,-1)
-    u = paintingData.fGradient[channel][(latticeIndex + 1) & kBlockMask].dot(fractionValue);
+    u = paintingData.fGradient[channel][b01].dot(fractionValue);
     SkScalar b = SkScalarInterp(u, v, sx);
     return SkScalarInterp(a, b, sy);
 }
@@ -989,13 +996,14 @@ void GrGLPerlinNoise::emitCode(GrGLShaderBuilder* builder,
     const char* chanCoord   = "chanCoord";
     const char* stitchData  = "stitchData";
     const char* ratio       = "ratio";
-    const char* noiseXY     = "noiseXY";
     const char* noiseVec    = "noiseVec";
     const char* noiseSmooth = "noiseSmooth";
+    const char* floorVal    = "floorVal";
     const char* fractVal    = "fractVal";
     const char* uv          = "uv";
     const char* ab          = "ab";
     const char* latticeIdx  = "latticeIdx";
+    const char* bcoords     = "bcoords";
     const char* lattice     = "lattice";
     const char* inc8bit     = "0.00390625";  // 1.0 / 256.0
     // This is the math to convert the two 16bit integer packed into rgba 8 bit input into a
@@ -1016,32 +1024,35 @@ void GrGLPerlinNoise::emitCode(GrGLShaderBuilder* builder,
 
     SkString noiseCode;
 
-    noiseCode.appendf("\tvec4 %s = vec4(floor(%s), fract(%s));", noiseXY, noiseVec, noiseVec);
+    noiseCode.appendf("\tvec4 %s;\n", floorVal);
+    noiseCode.appendf("\t%s.xy = floor(%s);\n", floorVal, noiseVec);
+    noiseCode.appendf("\t%s.zw = %s.xy + vec2(1.0);\n", floorVal, floorVal);
+    noiseCode.appendf("\tvec2 %s = fract(%s);\n", fractVal, noiseVec);
 
     // smooth curve : t * t * (3 - 2 * t)
-    noiseCode.appendf("\n\tvec2 %s = %s.zw * %s.zw * (vec2(3.0) - vec2(2.0) * %s.zw);",
-        noiseSmooth, noiseXY, noiseXY, noiseXY);
+    noiseCode.appendf("\n\tvec2 %s = %s * %s * (vec2(3.0) - vec2(2.0) * %s);",
+        noiseSmooth, fractVal, fractVal, fractVal);
 
     // Adjust frequencies if we're stitching tiles
     if (fStitchTiles) {
         noiseCode.appendf("\n\tif(%s.x >= %s.x) { %s.x -= %s.x; }",
-            noiseXY, stitchData, noiseXY, stitchData);
-        noiseCode.appendf("\n\tif(%s.x >= (%s.x - 1.0)) { %s.x -= (%s.x - 1.0); }",
-            noiseXY, stitchData, noiseXY, stitchData);
+            floorVal, stitchData, floorVal, stitchData);
         noiseCode.appendf("\n\tif(%s.y >= %s.y) { %s.y -= %s.y; }",
-            noiseXY, stitchData, noiseXY, stitchData);
-        noiseCode.appendf("\n\tif(%s.y >= (%s.y - 1.0)) { %s.y -= (%s.y - 1.0); }",
-            noiseXY, stitchData, noiseXY, stitchData);
+            floorVal, stitchData, floorVal, stitchData);
+        noiseCode.appendf("\n\tif(%s.z >= %s.x) { %s.z -= %s.x; }",
+            floorVal, stitchData, floorVal, stitchData);
+        noiseCode.appendf("\n\tif(%s.w >= %s.y) { %s.w -= %s.y; }",
+            floorVal, stitchData, floorVal, stitchData);
     }
 
     // Get texture coordinates and normalize
-    noiseCode.appendf("\n\t%s.xy = fract(floor(mod(%s.xy, 256.0)) / vec2(256.0));\n",
-        noiseXY, noiseXY);
+    noiseCode.appendf("\n\t%s = fract(floor(mod(%s, 256.0)) / vec4(256.0));\n",
+        floorVal, floorVal);
 
     // Get permutation for x
     {
         SkString xCoords("");
-        xCoords.appendf("vec2(%s.x, 0.5)", noiseXY);
+        xCoords.appendf("vec2(%s.x, 0.5)", floorVal);
 
         noiseCode.appendf("\n\tvec2 %s;\n\t%s.x = ", latticeIdx, latticeIdx);
         builder->appendTextureLookup(&noiseCode, samplers[0], xCoords.c_str(), kVec2f_GrSLType);
@@ -1051,7 +1062,7 @@ void GrGLPerlinNoise::emitCode(GrGLShaderBuilder* builder,
     // Get permutation for x + 1
     {
         SkString xCoords("");
-        xCoords.appendf("vec2(fract(%s.x + %s), 0.5)", noiseXY, inc8bit);
+        xCoords.appendf("vec2(%s.z, 0.5)", floorVal);
 
         noiseCode.appendf("\n\t%s.y = ", latticeIdx);
         builder->appendTextureLookup(&noiseCode, samplers[0], xCoords.c_str(), kVec2f_GrSLType);
@@ -1070,15 +1081,13 @@ void GrGLPerlinNoise::emitCode(GrGLShaderBuilder* builder,
 #endif
 
     // Get (x,y) coordinates with the permutated x
-    noiseCode.appendf("\n\t%s = fract(%s + %s.yy);", latticeIdx, latticeIdx, noiseXY);
-
-    noiseCode.appendf("\n\tvec2 %s = %s.zw;", fractVal, noiseXY);
+    noiseCode.appendf("\n\tvec4 %s = fract(%s.xyxy + %s.yyww);", bcoords, latticeIdx, floorVal);
 
     noiseCode.appendf("\n\n\tvec2 %s;", uv);
     // Compute u, at offset (0,0)
     {
         SkString latticeCoords("");
-        latticeCoords.appendf("vec2(%s.x, %s)", latticeIdx, chanCoord);
+        latticeCoords.appendf("vec2(%s.x, %s)", bcoords, chanCoord);
         noiseCode.appendf("\n\tvec4 %s = ", lattice);
         builder->appendTextureLookup(&noiseCode, samplers[1], latticeCoords.c_str(),
             kVec2f_GrSLType);
@@ -1090,7 +1099,7 @@ void GrGLPerlinNoise::emitCode(GrGLShaderBuilder* builder,
     // Compute v, at offset (-1,0)
     {
         SkString latticeCoords("");
-        latticeCoords.appendf("vec2(%s.y, %s)", latticeIdx, chanCoord);
+        latticeCoords.appendf("vec2(%s.y, %s)", bcoords, chanCoord);
         noiseCode.append("\n\tlattice = ");
         builder->appendTextureLookup(&noiseCode, samplers[1], latticeCoords.c_str(),
             kVec2f_GrSLType);
@@ -1106,7 +1115,7 @@ void GrGLPerlinNoise::emitCode(GrGLShaderBuilder* builder,
     // Compute v, at offset (-1,-1)
     {
         SkString latticeCoords("");
-        latticeCoords.appendf("vec2(fract(%s.y + %s), %s)", latticeIdx, inc8bit, chanCoord);
+        latticeCoords.appendf("vec2(%s.w, %s)", bcoords, chanCoord);
         noiseCode.append("\n\tlattice = ");
         builder->appendTextureLookup(&noiseCode, samplers[1], latticeCoords.c_str(),
             kVec2f_GrSLType);
@@ -1118,7 +1127,7 @@ void GrGLPerlinNoise::emitCode(GrGLShaderBuilder* builder,
     // Compute u, at offset (0,-1)
     {
         SkString latticeCoords("");
-        latticeCoords.appendf("vec2(fract(%s.x + %s), %s)", latticeIdx, inc8bit, chanCoord);
+        latticeCoords.appendf("vec2(%s.z, %s)", bcoords, chanCoord);
         noiseCode.append("\n\tlattice = ");
         builder->appendTextureLookup(&noiseCode, samplers[1], latticeCoords.c_str(),
             kVec2f_GrSLType);