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Optimize ProximityInfo#computeNearestNeighbors()

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This cuts the time spent in computeNearestNeigbors by
a factor of 6 to 20, with an average at about 8.
This method representing about 25% of the total time
spent when switching keyboards, this change is a
20% improvement in layout switching time.

Bug: 8689779
Change-Id: Icb465f6010b317c7156057891c3341e51a198688
This commit is contained in:
Jean Chalard 2013-06-03 18:42:55 +09:00
parent 27d9c6f795
commit d55baf06d9
1 changed files with 110 additions and 17 deletions
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127
java/src/com/android/inputmethod/keyboard/ProximityInfo.java
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@ -240,27 +240,120 @@ 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) {
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;
if (key.squaredDistanceToEdge(centerX, centerY) < threshold) {
neighborKeys[count++] = key;
/* 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;
}
baseIndexOfCurrentRow += mGridWidth;
}
}
mGridNeighbors[(y / mCellHeight) * mGridWidth + (x / mCellWidth)] =
Arrays.copyOfRange(neighborKeys, 0, count);
}
for (int i = 0; i < gridSize; ++i) {
final int base = i * keyCount;
mGridNeighbors[i] =
Arrays.copyOfRange(neighborsFlatBuffer, base, base + neighborCountPerCell[i]);
}
}