Use smoothstep to eliminate branches in AA shader

Change-Id: If4ecb1a9446f29b2f8444f5cee551f863c1993e8

2 files changed, 6 insertions, 29 deletions

diff --git a/libs/hwui/OpenGLRenderer.cpp b/libs/hwui/OpenGLRenderer.cpp
index 849c556..09dbf78 100644
--- a/libs/hwui/OpenGLRenderer.cpp
+++ b/libs/hwui/OpenGLRenderer.cpp
@@ -1403,10 +1403,6 @@ void OpenGLRenderer::setupDrawAALine(GLvoid* vertices, GLvoid* widthCoords,
 
     int boundaryWidthSlot = mCaches.currentProgram->getUniform("boundaryWidth");
     glUniform1f(boundaryWidthSlot, boundaryWidthProportion);
-
-    // Setting the inverse value saves computations per-fragment in the shader
-    int inverseBoundaryWidthSlot = mCaches.currentProgram->getUniform("inverseBoundaryWidth");
-    glUniform1f(inverseBoundaryWidthSlot, 1.0f / boundaryWidthProportion);
 }
 
 void OpenGLRenderer::finishDrawAALine(const int widthSlot, const int lengthSlot) {
@@ -1810,15 +1806,13 @@ void OpenGLRenderer::drawAARect(float left, float top, float right, float bottom
         float width = right - left;
         float height = bottom - top;
 
-        float boundaryWidthProportion = (width != 0) ? (2 * boundarySizeX) / width : 0;
-        float boundaryHeightProportion = (height != 0) ? (2 * boundarySizeY) / height : 0;
+        float boundaryWidthProportion = .5 - ((width != 0) ? (2 * boundarySizeX) / width : 0);
+        float boundaryHeightProportion = .5 - ((height != 0) ? (2 * boundarySizeY) / height : 0);
         setupDrawAALine((void*) aaVertices, widthCoords, lengthCoords,
                 boundaryWidthProportion, widthSlot, lengthSlot);
 
         int boundaryLengthSlot = mCaches.currentProgram->getUniform("boundaryLength");
-        int inverseBoundaryLengthSlot = mCaches.currentProgram->getUniform("inverseBoundaryLength");
         glUniform1f(boundaryLengthSlot, boundaryHeightProportion);
-        glUniform1f(inverseBoundaryLengthSlot, (1.0f / boundaryHeightProportion));
 
         AAVertex::set(aaVertices++, left, bottom, 1, 1);
         AAVertex::set(aaVertices++, left, top, 1, 0);
@@ -1955,9 +1949,7 @@ status_t OpenGLRenderer::drawLines(float* points, int count, SkPaint* paint) {
     Vertex* prevVertex = NULL;
 
     int boundaryLengthSlot = -1;
-    int inverseBoundaryLengthSlot = -1;
     int boundaryWidthSlot = -1;
-    int inverseBoundaryWidthSlot = -1;
 
     for (int i = 0; i < count; i += 4) {
         // a = start point, b = end point
@@ -2060,22 +2052,16 @@ status_t OpenGLRenderer::drawLines(float* points, int count, SkPaint* paint) {
                     if (boundaryWidthSlot < 0) {
                         boundaryWidthSlot =
                                 mCaches.currentProgram->getUniform("boundaryWidth");
-                        inverseBoundaryWidthSlot =
-                                mCaches.currentProgram->getUniform("inverseBoundaryWidth");
                     }
 
                     glUniform1f(boundaryWidthSlot, boundaryWidthProportion);
-                    glUniform1f(inverseBoundaryWidthSlot, (1 / boundaryWidthProportion));
                 }
 
                 if (boundaryLengthSlot < 0) {
                     boundaryLengthSlot = mCaches.currentProgram->getUniform("boundaryLength");
-                    inverseBoundaryLengthSlot =
-                            mCaches.currentProgram->getUniform("inverseBoundaryLength");
                 }
 
                 glUniform1f(boundaryLengthSlot, boundaryLengthProportion);
-                glUniform1f(inverseBoundaryLengthSlot, (1 / boundaryLengthProportion));
 
                 if (prevAAVertex != NULL) {
                     // Issue two repeat vertices to create degenerate triangles to bridge
diff --git a/libs/hwui/ProgramCache.cpp b/libs/hwui/ProgramCache.cpp
index d67bfbe..8a9a2ac 100644
--- a/libs/hwui/ProgramCache.cpp
+++ b/libs/hwui/ProgramCache.cpp
@@ -129,9 +129,7 @@ const char* gFS_Uniforms_Color =
         "uniform vec4 color;\n";
 const char* gFS_Uniforms_AA =
         "uniform float boundaryWidth;\n"
-        "uniform float inverseBoundaryWidth;\n"
-        "uniform float boundaryLength;\n"
-        "uniform float inverseBoundaryLength;\n";
+        "uniform float boundaryLength;\n";
 const char* gFS_Header_Uniforms_PointHasBitmap =
         "uniform vec2 textureDimension;\n"
         "uniform float pointSize;\n";
@@ -242,16 +240,9 @@ const char* gFS_Main_ModulateColor =
 const char* gFS_Main_ModulateColor_ApplyGamma =
         "    fragColor *= pow(color.a, gamma);\n";
 const char* gFS_Main_AccountForAA =
-        "    if (widthProportion < boundaryWidth) {\n"
-        "        fragColor *= (widthProportion * inverseBoundaryWidth);\n"
-        "    } else if (widthProportion > (1.0 - boundaryWidth)) {\n"
-        "        fragColor *= ((1.0 - widthProportion) * inverseBoundaryWidth);\n"
-        "    }\n"
-        "    if (lengthProportion < boundaryLength) {\n"
-        "        fragColor *= (lengthProportion * inverseBoundaryLength);\n"
-        "    } else if (lengthProportion > (1.0 - boundaryLength)) {\n"
-        "        fragColor *= ((1.0 - lengthProportion) * inverseBoundaryLength);\n"
-        "    }\n";
+        "    fragColor *= (1.0 - smoothstep(boundaryWidth, 0.5, abs(0.5 - widthProportion)))\n"
+        "               * (1.0 - smoothstep(boundaryLength, 0.5, abs(0.5 - lengthProportion)));\n";
+
 const char* gFS_Main_FetchTexture[2] = {
         // Don't modulate
         "    fragColor = texture2D(sampler, outTexCoords);\n",