Update Alligned Rect Shader to match geometry version

-Also update to combine width and height coverage using multiplication
 instead of using min

R=bsalomon@google.com, robertphillips@google.com

Author: egdaniel@google.com

Review URL: https://chromiumcodereview.appspot.com/16854012

git-svn-id: http://skia.googlecode.com/svn/trunk@9609 2bbb7eff-a529-9590-31e7-b0007b416f81

diff --git a/src/gpu/GrAARectRenderer.cpp b/src/gpu/GrAARectRenderer.cpp
index 7fe0517..0f0d1d4 100644 (file)
--- a/src/gpu/GrAARectRenderer.cpp
+++ b/src/gpu/GrAARectRenderer.cpp
@@ -59,23 +59,28 @@ public:
                 builder->getEffectAttributeName(drawEffect.getVertexAttribIndices()[0]);
             builder->vsCodeAppendf("\t%s = %s;\n", vsRectName, attr0Name->c_str());
 
-            // TODO: compute these scale factors in the VS
-            // These scale factors adjust the coverage for < 1 pixel wide/high rects
-            builder->fsCodeAppendf("\tfloat wScale = max(1.0, 2.0/(0.5+%s.z));\n",
-                                   fsRectName);
-            builder->fsCodeAppendf("\tfloat hScale = max(1.0, 2.0/(0.5+%s.w));\n",
-                                   fsRectName);
+            // TODO: compute all these offsets, spans, and scales in the VS
+            builder->fsCodeAppendf("\tfloat insetW = min(1.0, %s.z) - 0.5;\n", fsRectName);
+            builder->fsCodeAppendf("\tfloat insetH = min(1.0, %s.w) - 0.5;\n", fsRectName);
+            builder->fsCodeAppend("\tfloat outset = 0.5;\n");
+            // For rects > 1 pixel wide and tall the span's are noops (i.e., 1.0). For rects
+            // < 1 pixel wide or tall they serve to normalize the < 1 ramp to a 0 .. 1 range.
+            builder->fsCodeAppend("\tfloat spanW = insetW + outset;\n");
+            builder->fsCodeAppend("\tfloat spanH = insetH + outset;\n");
+            // For rects < 1 pixel wide or tall, these scale factors are used to cap the maximum
+            // value of coverage that is used. In other words it is the coverage that is
+            // used in the interior of the rect after the ramp.
+            builder->fsCodeAppend("\tfloat scaleW = min(1.0, 2*insetW/spanW);\n");
+            builder->fsCodeAppend("\tfloat scaleH = min(1.0, 2*insetH/spanH);\n");
 
             // Compute the coverage for the rect's width
-            builder->fsCodeAppendf("\tfloat coverage = clamp(wScale*(%s.z-abs(%s.x)), 0.0, 1.0);\n",
-                                   fsRectName,
-                                   fsRectName);
-
-            // Compute the coverage for the rect's height and merge with the width
             builder->fsCodeAppendf(
-                    "\tcoverage = min(coverage, clamp(hScale*(%s.w-abs(%s.y)), 0.0, 1.0));\n",
-                    fsRectName,
-                    fsRectName);
+                "\tfloat coverage = scaleW*clamp((%s.z-abs(%s.x))/spanW, 0.0, 1.0);\n", fsRectName,
+                fsRectName);
+            // Compute the coverage for the rect's height and merge with the width
+             builder->fsCodeAppendf(
+                 "\tcoverage = coverage*scaleH*clamp((%s.w-abs(%s.y))/spanH, 0.0, 1.0);\n",
+                 fsRectName, fsRectName);
 
             SkString modulate;
             GrGLSLModulatef<4>(&modulate, inputColor, "coverage");