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simplifying code to prevent drawing off-screen

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On certain graphics drivers, if you draw to a off-
screen buffer that's not used, it can lead to
poor performance. We were running into this in 
launcher; when setChildrenLayersEnabled was called
on a CellLayout, that triggered a re-draw of that
CellLayout's hardware layer, even if that
CellLayout wasn't visible. This CL changes
PagedView so that pages that aren't going to be
rendered are set to View.INVISIBLE, preventing
re-drawing of their hardware layer.
This commit is contained in:
Michael Jurka
2011-12-16 14:16:32 -08:00
parent 58e8b25c59
commit 80c69853d6
2 changed files with 21 additions and 42 deletions
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26
src/com/android/launcher2/PagedView.java
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@@ -727,17 +727,16 @@ public abstract class PagedView extends ViewGroup {
final int pageCount = getChildCount();
if (pageCount > 0) {
final int screenWidth = getMeasuredWidth();
int x = (int) getPageAt(0).getRight();
int leftScreen = 0;
int rightScreen = 0;
while (x <= mScrollX && leftScreen < pageCount - 1) {
while (leftScreen < pageCount - 1 &&
getPageAt(leftScreen).getRight() <= mScrollX) {
leftScreen++;
x = getPageAt(leftScreen).getRight();
}
rightScreen = leftScreen;
while (x < mScrollX + screenWidth && rightScreen < pageCount - 1) {
while (rightScreen < pageCount - 1 &&
getPageAt(rightScreen + 1).getLeft() < mScrollX + screenWidth) {
rightScreen++;
x = (int) getPageAt(rightScreen).getRight();
}
range[0] = leftScreen;
range[1] = rightScreen;
@@ -773,8 +772,21 @@ public abstract class PagedView extends ViewGroup {
canvas.clipRect(mScrollX, mScrollY, mScrollX + mRight - mLeft,
mScrollY + mBottom - mTop);
for (int i = rightScreen; i >= leftScreen; i--) {
drawChild(canvas, getPageAt(i), drawingTime);
// On certain graphics drivers, if you draw to a off-screen buffer that's not
// used, it can lead to poor performance. We were running into this when
// setChildrenLayersEnabled was called on a CellLayout; that triggered a re-draw
// of that CellLayout's hardware layer, even if that CellLayout wasn't visible.
// As a fix, below we set pages that aren't going to be rendered are to be
// View.INVISIBLE, preventing re-drawing of their hardware layer
for (int i = getChildCount() - 1; i >= 0; i--) {
final View v = getPageAt(i);
if (leftScreen <= i && i <= rightScreen &&
v.getAlpha() > ViewConfiguration.ALPHA_THRESHOLD) {
v.setVisibility(VISIBLE);
drawChild(canvas, v, drawingTime);
} else {
v.setVisibility(INVISIBLE);
}
}
canvas.restore();
}