Enabling Perlin Noise on Android

src/effects/SkPerlinNoiseShader.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkDither.h"
 #include "SkPerlinNoiseShader.h"
 #include "SkFlattenableBuffers.h"
@@ skipping 476 matching lines @@
     for (int i = 0; i < count; ++i) {
         unsigned dither = DITHER_VALUE(x);
         result[i] = SkDitherRGB32To565(shade(point, stitchData), dither);
         DITHER_INC_X(x);
         point.fX += SK_Scalar1;
     }
 }
 
 /////////////////////////////////////////////////////////////////////
 
-#if SK_SUPPORT_GPU && !defined(SK_BUILD_FOR_ANDROID)
-// CPU noise is faster on Android, so the GPU implementation is only for desktop
+#if SK_SUPPORT_GPU
 
 #include "GrTBackendEffectFactory.h"
 
 class GrGLNoise : public GrGLEffect {
 public:
     GrGLNoise(const GrBackendEffectFactory& factory,
               const GrDrawEffect& drawEffect);
     virtual ~GrGLNoise() {}
 
     static inline EffectKey GenKey(const GrDrawEffect&, const GrGLCaps&);
@@ skipping 492 matching lines @@
     const char* uv          = "uv";
     const char* ab          = "ab";
     const char* latticeIdx  = "latticeIdx";
     const char* lattice     = "lattice";
     const char* perlinNoise = "4096.0";
     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
     // [-1,1] vector and perform a dot product between that vector and the provided vector.
     const char* dotLattice  = "dot(((%s.ga + %s.rb * vec2(%s)) * vec2(2.0) - vec2(1.0)), %s);";
 
+    // Android precision fix for NON Tegra devices, like, for example: Nexus 10 (ARM's Mali-T604)
+    // The value of perlinNoise is 4096.0, so we need a high precision float to store this
+    const GrGLShaderVar::Precision precision = GrGLShaderVar::kHigh_Precision;
+    const char* precisionString =
+        GrGLShaderVar::PrecisionString(precision, builder->ctxInfo().binding());
+
     // Add noise function
     static const GrGLShaderVar gPerlinNoiseArgs[] =  {
         GrGLShaderVar(chanCoord, kFloat_GrSLType),
-        GrGLShaderVar(noiseVec, kVec2f_GrSLType)
+        GrGLShaderVar(noiseVec, kVec2f_GrSLType, GrGLShaderVar::kNonArray, precision)
     };
 
     static const GrGLShaderVar gPerlinNoiseStitchArgs[] =  {
         GrGLShaderVar(chanCoord, kFloat_GrSLType),
-        GrGLShaderVar(noiseVec, kVec2f_GrSLType),
-        GrGLShaderVar(stitchData, kVec4f_GrSLType)
+        GrGLShaderVar(noiseVec, kVec2f_GrSLType, GrGLShaderVar::kNonArray, precision),
+        GrGLShaderVar(stitchData, kVec4f_GrSLType, GrGLShaderVar::kNonArray, precision)
     };
 
     SkString noiseCode;
 
     noiseCode.appendf(
-        "\tvec4 %s = vec4(floor(%s) + vec2(%s), fract(%s));",
-        noiseXY, noiseVec, perlinNoise, noiseVec);
+        "\t%svec4 %s = vec4(floor(%s) + vec2(%s), fract(%s));",
+        precisionString, noiseXY, noiseVec, perlinNoise, 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);
 
     // Adjust frequencies if we're stitching tiles
     if (fStitchTiles) {
         noiseCode.appendf("\n\tif(%s.x >= %s.y) { %s.x -= %s.x; }",
             noiseXY, stitchData, noiseXY, stitchData);
         noiseCode.appendf("\n\tif(%s.x >= (%s.y - 1.0)) { %s.x -= (%s.x - 1.0); }",
@@ skipping 21 matching lines @@
     // Get permutation for x + 1
     {
         SkString xCoords("");
         xCoords.appendf("vec2(fract(%s.x + %s), 0.5)", noiseXY, inc8bit);
 
         noiseCode.appendf("\n\t%s.y = ", latticeIdx);
         builder->appendTextureLookup(&noiseCode, samplers[0], xCoords.c_str(), kVec2f_GrSLType);
         noiseCode.append(".r;");
     }
 
+#if defined(SK_BUILD_FOR_ANDROID)
+    // Android rounding for Tegra devices, like, for example: Xoom (Tegra 2), Nexus 7 (Tegra 3).
+    // The issue is that colors aren't accurate enough on Tegra devices. For example, if an 8 bit
+    // value of 124 (or 0.486275 here) is entered, we can get a texture value of 123.513725
+    // (or 0.484368 here). The following rounding operation prevents these precision issues from
+    // affecting the result of the noise by making sure that we only have multiples of 1/255.
+    // (Note that 1/255 is about 0.003921569, which is the value used here).
+    noiseCode.appendf("\n\t%s = floor(%s * vec2(255.0) + vec2(0.5)) * vec2(0.003921569);",
+                      latticeIdx, latticeIdx);
+#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\n\tvec2 %s;", uv);
     // Compute u, at offset (0,0)
     {
         SkString latticeCoords("");
         latticeCoords.appendf("vec2(%s.x, %s)", latticeIdx, chanCoord);
         noiseCode.appendf("\n\tvec4 %s = ", lattice);
         builder->appendTextureLookup(&noiseCode, samplers[1], latticeCoords.c_str(),
             kVec2f_GrSLType);
         noiseCode.appendf(".bgra;\n\t%s.x = ", uv);
         noiseCode.appendf(dotLattice, lattice, lattice, inc8bit, fractVal);
     }
 
     noiseCode.appendf("\n\t%s.x -= 1.0;", fractVal);
     // Compute v, at offset (-1,0)
     {
         SkString latticeCoords("");
         latticeCoords.appendf("vec2(%s.y, %s)", latticeIdx, chanCoord);
-        noiseCode.append("lattice = ");
+        noiseCode.append("\n\tlattice = ");
         builder->appendTextureLookup(&noiseCode, samplers[1], latticeCoords.c_str(),
             kVec2f_GrSLType);
         noiseCode.appendf(".bgra;\n\t%s.y = ", uv);
         noiseCode.appendf(dotLattice, lattice, lattice, inc8bit, fractVal);
     }
 
     // Compute 'a' as a linear interpolation of 'u' and 'v'
     noiseCode.appendf("\n\tvec2 %s;", ab);
     noiseCode.appendf("\n\t%s.x = mix(%s.x, %s.y, %s.x);", ab, uv, uv, noiseSmooth);
 
     noiseCode.appendf("\n\t%s.y -= 1.0;", fractVal);
     // Compute v, at offset (-1,-1)
     {
         SkString latticeCoords("");
         latticeCoords.appendf("vec2(fract(%s.y + %s), %s)", latticeIdx, inc8bit, chanCoord);
-        noiseCode.append("lattice = ");
+        noiseCode.append("\n\tlattice = ");
         builder->appendTextureLookup(&noiseCode, samplers[1], latticeCoords.c_str(),
             kVec2f_GrSLType);
         noiseCode.appendf(".bgra;\n\t%s.y = ", uv);
         noiseCode.appendf(dotLattice, lattice, lattice, inc8bit, fractVal);
     }
 
     noiseCode.appendf("\n\t%s.x += 1.0;", fractVal);
     // Compute u, at offset (0,-1)
     {
         SkString latticeCoords("");
         latticeCoords.appendf("vec2(fract(%s.x + %s), %s)", latticeIdx, inc8bit, chanCoord);
-        noiseCode.append("lattice = ");
+        noiseCode.append("\n\tlattice = ");
         builder->appendTextureLookup(&noiseCode, samplers[1], latticeCoords.c_str(),
             kVec2f_GrSLType);
         noiseCode.appendf(".bgra;\n\t%s.x = ", uv);
         noiseCode.appendf(dotLattice, lattice, lattice, inc8bit, fractVal);
     }
 
     // Compute 'b' as a linear interpolation of 'u' and 'v'
     noiseCode.appendf("\n\t%s.y = mix(%s.x, %s.y, %s.x);", ab, uv, uv, noiseSmooth);
     // Compute the noise as a linear interpolation of 'a' and 'b'
     noiseCode.appendf("\n\treturn mix(%s.x, %s.y, %s.y);\n", ab, ab, noiseSmooth);
 
     SkString noiseFuncName;
     if (fStitchTiles) {
-        builder->emitFunction(GrGLShaderBuilder::kFragment_ShaderType, kFloat_GrSLType, "perlinnoise",
-                              SK_ARRAY_COUNT(gPerlinNoiseStitchArgs), gPerlinNoiseStitchArgs,
-                              noiseCode.c_str(), &noiseFuncName);
+        builder->emitFunction(GrGLShaderBuilder::kFragment_ShaderType, kFloat_GrSLType,
+                              "perlinnoise", SK_ARRAY_COUNT(gPerlinNoiseStitchArgs),
+                              gPerlinNoiseStitchArgs, noiseCode.c_str(), &noiseFuncName);
     } else {
-        builder->emitFunction(GrGLShaderBuilder::kFragment_ShaderType, kFloat_GrSLType, "perlinnoise",
-                              SK_ARRAY_COUNT(gPerlinNoiseArgs), gPerlinNoiseArgs,
-                              noiseCode.c_str(), &noiseFuncName);
+        builder->emitFunction(GrGLShaderBuilder::kFragment_ShaderType, kFloat_GrSLType,
+                              "perlinnoise", SK_ARRAY_COUNT(gPerlinNoiseArgs),
+                              gPerlinNoiseArgs, noiseCode.c_str(), &noiseFuncName);
     }
 
     // There are rounding errors if the floor operation is not performed here
     builder->fsCodeAppendf("\n\t\tvec2 %s = floor((%s * vec3(%s, 1.0)).xy) * %s;",
                            noiseVec, invMatrixUni, vCoords, baseFrequencyUni);
 
     // Clear the color accumulator
     builder->fsCodeAppendf("\n\t\t%s = vec4(0.0);", outputColor);
 
     if (fStitchTiles) {
         // Set up TurbulenceInitial stitch values.
-        builder->fsCodeAppendf("\n\t\tvec4 %s = %s;", stitchData, stitchDataUni);
+        builder->fsCodeAppendf("\n\t\t%s vec4 %s = %s;", precisionString, stitchData, stitchDataUni);
     }
 
     builder->fsCodeAppendf("\n\t\tfloat %s = 1.0;", ratio);
 
     // Loop over all octaves
     builder->fsCodeAppendf("\n\t\tfor (int octave = 0; octave < %d; ++octave) {", fNumOctaves);
 
     builder->fsCodeAppendf("\n\t\t\t%s += ", outputColor);
     if (fType != SkPerlinNoiseShader::kFractalNoise_Type) {
         builder->fsCodeAppend("abs(");
@@ skipping 18 matching lines @@
     if (fType != SkPerlinNoiseShader::kFractalNoise_Type) {
         builder->fsCodeAppendf(")"); // end of "abs("
     }
     builder->fsCodeAppendf(" * %s;", ratio);
 
     builder->fsCodeAppendf("\n\t\t\t%s *= vec2(2.0);", noiseVec);
     builder->fsCodeAppendf("\n\t\t\t%s *= 0.5;", ratio);
 
     if (fStitchTiles) {
         builder->fsCodeAppendf("\n\t\t\t%s.xz *= vec2(2.0);", stitchData);
-        builder->fsCodeAppendf("\n\t\t\t%s.yw = %s.xz + vec2(%s);", stitchData, stitchData, perlinNoise);
+        builder->fsCodeAppendf("\n\t\t\t%s.yw = %s.xz + vec2(%s);",
+                               stitchData, stitchData, perlinNoise);
     }
     builder->fsCodeAppend("\n\t\t}"); // end of the for loop on octaves
 
     if (fType == SkPerlinNoiseShader::kFractalNoise_Type) {
         // The value of turbulenceFunctionResult comes from ((turbulenceFunctionResult) + 1) / 2
         // by fractalNoise and (turbulenceFunctionResult) by turbulence.
         builder->fsCodeAppendf("\n\t\t%s = %s * vec4(0.5) + vec4(0.5);", outputColor, outputColor);
     }
 
     builder->fsCodeAppendf("\n\t\t%s.a *= %s;", outputColor, alphaUni);
@@ skipping 126 matching lines @@
         GrUnlockAndUnrefCachedBitmapTexture(noiseTexture);
     }
 #endif
 
     return effect;
 }
 
 #else
 
 GrEffectRef* SkPerlinNoiseShader::asNewEffect(GrContext*, const SkPaint&) const {
-#if !defined(SK_BUILD_FOR_ANDROID)
     SkDEBUGFAIL("Should not call in GPU-less build");
-#endif
     return NULL;
 }
 
 #endif
 
 #ifdef SK_DEVELOPER
 void SkPerlinNoiseShader::toString(SkString* str) const {
     str->append("SkPerlinNoiseShader: (");
 
     str->append("type: ");
@@ skipping 17 matching lines @@
     str->append(" seed: ");
     str->appendScalar(fSeed);
     str->append(" stitch tiles: ");
     str->append(fStitchTiles ? "true " : "false ");
 
     this->INHERITED::toString(str);
 
     str->append(")");
 }
 #endif