diff --git a/java/src/com/android/inputmethod/keyboard/ProximityInfo.java b/java/src/com/android/inputmethod/keyboard/ProximityInfo.java
index 57d3fede4c3fceca5dd7eee745b2bd3ee4c2710c..0e86b051de898deb72a49c51c9b6e6fdb2ac4d6e 100644
--- a/java/src/com/android/inputmethod/keyboard/ProximityInfo.java
+++ b/java/src/com/android/inputmethod/keyboard/ProximityInfo.java
@@ -240,28 +240,121 @@ public class ProximityInfo {
private void computeNearestNeighbors() {
final int defaultWidth = mMostCommonKeyWidth;
- final Key[] keys = mKeys;
- final int thresholdBase = (int) (defaultWidth * SEARCH_DISTANCE);
- final int threshold = thresholdBase * thresholdBase;
+ final int keyCount = mKeys.length;
+ final int gridSize = mGridNeighbors.length;
+ final int threshold = (int) (defaultWidth * SEARCH_DISTANCE);
+ final int thresholdSquared = threshold * threshold;
// Round-up so we don't have any pixels outside the grid
- final Key[] neighborKeys = new Key[keys.length];
- final int gridWidth = mGridWidth * mCellWidth;
- final int gridHeight = mGridHeight * mCellHeight;
- for (int x = 0; x < gridWidth; x += mCellWidth) {
- for (int y = 0; y < gridHeight; y += mCellHeight) {
- final int centerX = x + mCellWidth / 2;
- final int centerY = y + mCellHeight / 2;
- int count = 0;
- for (final Key key : keys) {
- if (key.isSpacer()) continue;
- if (key.squaredDistanceToEdge(centerX, centerY) < threshold) {
- neighborKeys[count++] = key;
+ final int fullGridWidth = mGridWidth * mCellWidth;
+ final int fullGridHeight = mGridHeight * mCellHeight;
+
+ // For large layouts, 'neighborsFlatBuffer' is about 80k of memory: gridSize is usually 512,
+ // keycount is about 40 and a pointer to a Key is 4 bytes. This contains, for each cell,
+ // enough space for as many keys as there are on the keyboard. Hence, every
+ // keycount'th element is the start of a new cell, and each of these virtual subarrays
+ // start empty with keycount spaces available. This fills up gradually in the loop below.
+ // Since in the practice each cell does not have a lot of neighbors, most of this space is
+ // actually just empty padding in this fixed-size buffer.
+ final Key[] neighborsFlatBuffer = new Key[gridSize * keyCount];
+ final int[] neighborCountPerCell = new int[gridSize];
+ final int halfCellWidth = mCellWidth / 2;
+ final int halfCellHeight = mCellHeight / 2;
+ for (final Key key : mKeys) {
+ if (key.isSpacer()) continue;
+
+/* HOW WE PRE-SELECT THE CELLS (iterate over only the relevant cells, instead of all of them)
+
+ We want to compute the distance for keys that are in the cells that are close enough to the
+ key border, as this method is performance-critical. These keys are represented with 'star'
+ background on the diagram below. Let's consider the Y case first.
+
+ We want to select the cells which center falls between the top of the key minus the threshold,
+ and the bottom of the key plus the threshold.
+ topPixelWithinThreshold is key.mY - threshold, and bottomPixelWithinThreshold is
+ key.mY + key.mHeight + threshold.
+
+ Then we need to compute the center of the top row that we need to evaluate, as we'll iterate
+ from there.
+
+(0,0)----> x
+| .-------------------------------------------.
+| | | | | | | | | | | | |
+| |---+---+---+---+---+---+---+---+---+---+---| .- top of top cell (aligned on the grid)
+| | | | | | | | | | | | | |
+| |-----------+---+---+---+---+---+---+---+---|---' v
+| | | | |***|***|*_________________________ topPixelWithinThreshold | yDeltaToGrid
+| |---+---+---+-----^-+-|-+---+---+---+---+---| ^
+| | | | |***|*|*|*|*|***|***| | | | ______________________________________
+v |---+---+--threshold--|-+---+---+---+---+---| |
+ | | | |***|*|*|*|*|***|***| | | | | Starting from key.mY, we substract
+y |---+---+---+---+-v-+-|-+---+---+---+---+---| | thresholdBase and get the top pixel
+ | | | |***|**########------------------- key.mY | within the threshold. We align that on
+ |---+---+---+---+--#+---+-#-+---+---+---+---| | the grid by computing the delta to the
+ | | | |***|**#|***|*#*|***| | | | | grid, and get the top of the top cell.
+ |---+---+---+---+--#+---+-#-+---+---+---+---| |
+ | | | |***|**########*|***| | | | | Adding half the cell height to the top
+ |---+---+---+---+---+-|-+---+---+---+---+---| | of the top cell, we get the middle of
+ | | | |***|***|*|*|***|***| | | | | the top cell (yMiddleOfTopCell).
+ |---+---+---+---+---+-|-+---+---+---+---+---| |
+ | | | |***|***|*|*|***|***| | | | |
+ |---+---+---+---+---+-|________________________ yEnd | Since we only want to add the key to
+ | | | | | | | (bottomPixelWithinThreshold) | the proximity if it's close enough to
+ |---+---+---+---+---+---+---+---+---+---+---| | the center of the cell, we only need
+ | | | | | | | | | | | | | to compute for these cells where
+ '---'---'---'---'---'---'---'---'---'---'---' | topPixelWithinThreshold is above the
+ (positive x,y) | center of the cell. This is the case
+ | when yDeltaToGrid is less than half
+ [Zoomed in diagram] | the height of the cell.
+ +-------+-------+-------+-------+-------+ |
+ | | | | | | | On the zoomed in diagram, on the right
+ | | | | | | | the topPixelWithinThreshold (represented
+ | | | | | | top of | with an = sign) is below and we can skip
+ +-------+-------+-------+--v----+-------+ .. top cell | this cell, while on the left it's above
+ | | = topPixelWT | | yDeltaToGrid | and we need to compute for this cell.
+ |..yStart.|.....|.......|..|....|.......|... y middle | Thus, if yDeltaToGrid is more than half
+ | (left)| | | ^ = | | of top cell | the height of the cell, we start the
+ +-------+-|-----+-------+----|--+-------+ | iteration one cell below the top cell,
+ | | | | | | | | | else we start it on the top cell. This
+ |.......|.|.....|.......|....|..|.....yStart (right) | is stored in yStart.
+
+ Since we only want to go up to bottomPixelWithinThreshold, and we only iterate on the center
+ of the keys, we can stop as soon as the y value exceeds bottomPixelThreshold, so we don't
+ have to align this on the center of the key. Hence, we don't need a separate value for
+ bottomPixelWithinThreshold and call this yEnd right away.
+*/
+ final int topPixelWithinThreshold = key.mY - threshold;
+ final int yDeltaToGrid = topPixelWithinThreshold % mCellHeight;
+ final int yMiddleOfTopCell = topPixelWithinThreshold - yDeltaToGrid + halfCellHeight;
+ final int yStart = Math.max(halfCellHeight,
+ yMiddleOfTopCell + (yDeltaToGrid <= halfCellHeight ? 0 : mCellHeight));
+ final int yEnd = Math.min(fullGridHeight, key.mY + key.mHeight + threshold);
+
+ final int leftPixelWithinThreshold = key.mX - threshold;
+ final int xDeltaToGrid = leftPixelWithinThreshold % mCellWidth;
+ final int xMiddleOfLeftCell = leftPixelWithinThreshold - xDeltaToGrid + halfCellWidth;
+ final int xStart = Math.max(halfCellWidth,
+ xMiddleOfLeftCell + (xDeltaToGrid <= halfCellWidth ? 0 : mCellWidth));
+ final int xEnd = Math.min(fullGridWidth, key.mX + key.mWidth + threshold);
+
+ int baseIndexOfCurrentRow = (yStart / mCellHeight) * mGridWidth + (xStart / mCellWidth);
+ for (int centerY = yStart; centerY <= yEnd; centerY += mCellHeight) {
+ int index = baseIndexOfCurrentRow;
+ for (int centerX = xStart; centerX <= xEnd; centerX += mCellWidth) {
+ if (key.squaredDistanceToEdge(centerX, centerY) < thresholdSquared) {
+ neighborsFlatBuffer[index * keyCount + neighborCountPerCell[index]] = key;
+ ++neighborCountPerCell[index];
}
+ ++index;
}
- mGridNeighbors[(y / mCellHeight) * mGridWidth + (x / mCellWidth)] =
- Arrays.copyOfRange(neighborKeys, 0, count);
+ baseIndexOfCurrentRow += mGridWidth;
}
}
+
+ for (int i = 0; i < gridSize; ++i) {
+ final int base = i * keyCount;
+ mGridNeighbors[i] =
+ Arrays.copyOfRange(neighborsFlatBuffer, base, base + neighborCountPerCell[i]);
+ }
}
public void fillArrayWithNearestKeyCodes(final int x, final int y, final int primaryKeyCode,