made point lights linear attenuation; also fixed point light depth bug

src/core/SkShadowShader.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCanvas.h"
 #include "SkReadBuffer.h"
 #include "SkShadowShader.h"
@@ skipping 272 matching lines @@
                 SkString povCoord("povCoord");
                 povCoord.appendf("%d", i);
 
                 SkString offset("offset");
                 offset.appendf("%d", i);
                 fragBuilder->codeAppendf("vec2 %s;", offset.c_str());
 
                 if (shadowFP.fIsPointLight[i]) {
                     fragBuilder->codeAppendf("vec3 fragToLight%d = %s - worldCor;",
                                              i, lightDirOrPosUniName[i]);
-                    fragBuilder->codeAppendf("float distsq%d = dot(fragToLight%d, "
-                                                     "fragToLight%d);",
-                                             i, i, i);
+                    fragBuilder->codeAppendf("float dist%d = length(fragToLight%d);",
+                                             i, i);
                     fragBuilder->codeAppendf("%s = vec2(-fragToLight%d) * povDepth.b;",
                                              offset.c_str(), i);
                     fragBuilder->codeAppendf("fragToLight%d = normalize(fragToLight%d);",
                                              i, i);
                 }
 
                 if (shadowFP.fIsRadialLight[i]) {
                     fragBuilder->codeAppendf("vec2 %s = vec2(vMatrixCoord_0_1_Stage0.x, "
                                                             "1 - vMatrixCoord_0_1_Stage0.y);\n",
                                              povCoord.c_str());
@@ skipping 70 matching lines @@
 
                 if (shadowFP.fIsRadialLight[i]) {
                     fragBuilder->codeAppend("totalLightColor = vec3(0);");
 
                     fragBuilder->codeAppend("vec2 tc = vec2(povCoord0.x, 0.0);");
                     fragBuilder->codeAppend("float depth = texture(uTextureSampler0_Stage1,"
                                                                   "povCoord0).b * 2.0;");
 
                     fragBuilder->codeAppendf("lightProbability = step(r, depth);");
 
-                    fragBuilder->codeAppendf("if (%s.b != 0 || depth == 0) {"
+                    // 2 is the maximum depth. If this is reached, probably we have
+                    // not intersected anything. So values after this should be unshadowed.
+                    fragBuilder->codeAppendf("if (%s.b != 0 || depth == 2) {"
                                                      "lightProbability = 1.0; }",
                                              povDepth.c_str());
                 } else {
                     // 1/512 == .00195... is less than half a pixel; imperceptible
                     fragBuilder->codeAppendf("if (%s.b <= %s.b + .001953125) {",
                                              povDepth.c_str(), depthMaps[i].c_str());
                     if (blurAlgorithm == SkShadowParams::kVariance_ShadowType) {
                         // We mess with depth and depth^2 in their given scales.
                         // (i.e. between 0 and 1)
                         fragBuilder->codeAppendf("vec2 moments%d = vec2(%s.b, %s.g);",
@@ skipping 27 matching lines @@
                         fragBuilder->codeAppendf("} else { lightProbability = 0; }");
                     }
 
                     // VSM: The curved shadows near plane edges are artifacts from blurring
                     // lightDir.z is equal to the lightDir dot the surface normal.
                     fragBuilder->codeAppendf("}");
                 }
 
                 if (shadowFP.isPointLight(i)) {
                     fragBuilder->codeAppendf("totalLightColor += max(fragToLight%d.z, 0) * %s /"
-                                                     "(1 + distsq%d) * lightProbability;",
+                                                     "(1 + dist%d) * lightProbability;",
                                              i, lightColorUniName[i], i);
                 } else {
                     fragBuilder->codeAppendf("totalLightColor += %s.z * %s * lightProbability;",
                                              lightDirOrPosUniName[i],
                                              lightColorUniName[i]);
                 }
 
                 fragBuilder->codeAppendf("totalLightColor += %s;", ambientColorUniName);
                 fragBuilder->codeAppendf("%s = resultDiffuseColor * vec4(totalLightColor, 1);",
                                          args.fOutputColor);
@@ skipping 366 matching lines @@
 
                     int height = lightShader.fDiffuseHeight;
 
                     SkVector3 fragToLight = SkVector3::Make(light.pos().fX - x - i,
                                                             light.pos().fY - (height - y),
                                                             light.pos().fZ - pvDepth);
 
                     SkScalar dist = fragToLight.length();
                     SkScalar normalizedZ = fragToLight.fZ / dist;
 
-                    SkScalar distAttenuation = light.intensity() / (1.0f + dist * dist);
+                    SkScalar distAttenuation = light.intensity() / (1.0f + dist);
 
                     // assume object normals are pointing straight up
                     totalLight.fX += normalizedZ * light.color().fX * distAttenuation;
                     totalLight.fY += normalizedZ * light.color().fY * distAttenuation;
                     totalLight.fZ += normalizedZ * light.color().fZ * distAttenuation;
                 }
             }
 
             SkColor3f totalColor = SkColor3f::Make(SkColorGetR(diffColor) * totalLight.fX,
                                                    SkColorGetG(diffColor) * totalLight.fY,
@@ skipping 115 matching lines @@
 
 ///////////////////////////////////////////////////////////////////////////////
 
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkShadowShader)
     SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkShadowShaderImpl)
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END
 
 ///////////////////////////////////////////////////////////////////////////////
 
 #endif