First pass at new FolderIcon visual treatment

-> Modeled as a set of items around a circle
-> Modulate the radius and icon size as number of items grow
-> Clip the icons by a circular clip aligned to the background drawable

Remaining issues
-> Probably want to move to a programmaticly drawn circle + shadow
-> Anti-aliasing of the clipped region will need more attention
-> Need to animate all items in the preview as it changes (this
   wasn't required before)

Change-Id: I678ec605f6c8a34e9d7e4aec4e9583e36a9ef394

src/com/android/launcher3/folder/ClippedFolderIconLayoutRule.java

@@ -0,0 +1,128 @@
+package com.android.launcher3.folder;
+
+import android.graphics.Path;
+import android.graphics.Point;
+
+import com.android.launcher3.DeviceProfile;
+import com.android.launcher3.LauncherAppState;
+import com.android.launcher3.Utilities;
+
+public class ClippedFolderIconLayoutRule implements FolderIcon.PreviewLayoutRule {
+
+    static final int MAX_NUM_ITEMS_IN_PREVIEW = 4;
+    private static final int MIN_NUM_ITEMS_IN_PREVIEW = 2;
+
+    final float MIN_SCALE = 0.48f;
+    final float MAX_SCALE = 0.58f;
+    final float MAX_RADIUS_DILATION = 0.15f;
+
+    private float[] mTmpPoint = new float[2];
+
+    private float mAvailableSpace;
+    private float mRadius;
+    private float mIconSize;
+    private boolean mIsRtl;
+    private Path mClipPath = new Path();
+
+    @Override
+    public void init(int availableSpace, int intrinsicIconSize, boolean rtl) {
+        mAvailableSpace = availableSpace;
+        mRadius = 0.66f * availableSpace;
+        mIconSize = intrinsicIconSize;
+        mIsRtl = rtl;
+
+        // We make the clip radius just slightly smaller than the background drawable
+        // TODO(adamcohen): this is hacky, needs cleanup (likely through programmatic drawing).
+        int clipRadius = (int) mAvailableSpace / 2 - 1;
+
+        mClipPath.addCircle(mAvailableSpace / 2, mAvailableSpace / 2, clipRadius, Path.Direction.CW);
+    }
+
+    @Override
+    public FolderIcon.PreviewItemDrawingParams computePreviewItemDrawingParams(int index,
+            int curNumItems, FolderIcon.PreviewItemDrawingParams params) {
+
+        getPosition(index, curNumItems, mTmpPoint);
+
+        float transX = mTmpPoint[0];
+        float transY = mTmpPoint[1];
+        float totalScale = scaleForNumItems(curNumItems);
+        float overlayAlpha = 0;
+
+        if (params == null) {
+            params = new FolderIcon.PreviewItemDrawingParams(transX, transY, totalScale, overlayAlpha);
+        } else {
+            params.transX = transX;
+            params.transY = transY;
+            params.scale = totalScale;
+            params.overlayAlpha = overlayAlpha;
+        }
+
+        return params;
+    }
+
+    private void getPosition(int index, int curNumItems, float[] result) {
+        // The case of two items is homomorphic to the case of one.
+        curNumItems = Math.max(curNumItems, 2);
+
+
+        // We model the preview as a circle of items starting in the appropriate piece of the
+        // upper left quadrant (to achieve horizontal and vertical symmetry).
+        double theta0 = mIsRtl ? 0 : Math.PI;
+
+        // In RTL we go counterclockwise
+        int direction = mIsRtl ? 1 : -1;
+
+        double thetaShift = 0;
+        if (curNumItems == 3) {
+            thetaShift = Math.PI / 6;
+        } else if (curNumItems == 4) {
+            thetaShift = Math.PI / 4;
+        }
+        theta0 += direction * thetaShift;
+
+        // We want the items to appear in reading order. For the case of 1, 2 and 3 items, this
+        // is natural for the circular model. With 4 items, however, we need to swap the 3rd and
+        // 4th indices to achieve reading order.
+        if (curNumItems == 4 && index == 3) {
+            index = 2;
+        } else if (curNumItems == 4 && index == 2) {
+            index = 3;
+        }
+
+        // We bump the radius up between 0 and MAX_RADIUS_DILATION % as the number of items increase
+        float radius = mRadius * (1 + MAX_RADIUS_DILATION * (curNumItems -
+                MIN_NUM_ITEMS_IN_PREVIEW) / (MAX_NUM_ITEMS_IN_PREVIEW - MIN_NUM_ITEMS_IN_PREVIEW));
+        double theta = theta0 + index * (2 * Math.PI / curNumItems) * direction;
+
+        float halfIconSize = (mIconSize * scaleForNumItems(curNumItems)) / 2;
+
+        // Map the location along the circle, and offset the coordinates to represent the center
+        // of the icon, and to be based from the top / left of the preview area. The y component
+        // is inverted to match the coordinate system.
+        result[0] = mAvailableSpace / 2 + (float) (radius * Math.cos(theta) / 2) - halfIconSize;
+        result[1] = mAvailableSpace / 2 + (float) (- radius * Math.sin(theta) / 2) - halfIconSize;
+
+    }
+
+    private float scaleForNumItems(int numItems) {
+        if (numItems <= 2) {
+            return MAX_SCALE;
+        } else if (numItems == 3) {
+            return (MAX_SCALE + MIN_SCALE) / 2;
+        } else {
+            return MIN_SCALE;
+        }
+    }
+
+    @Override
+    public int numItems() {
+        return MAX_NUM_ITEMS_IN_PREVIEW;
+    }
+
+    @Override
+    public Path getClipPath() {
+        return mClipPath;
+    }
+
+}