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Add comments to FlatViewGroup, DrawCommandManage, ElementsList and StateBuilder.

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Summary: Documentate all of the things.

Reviewed By: ahmedre

Differential Revision: D3700420
This commit is contained in:
Seth Kirby
2016-08-15 14:16:53 -07:00
committed by Ahmed El-Helw
parent 3adbf1e822
commit 8600723402
8 changed files with 656 additions and 74 deletions
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193
ReactAndroid/src/main/java/com/facebook/react/flat/ClippingDrawCommandManager.java
View File

@@ -27,8 +27,123 @@ import com.facebook.infer.annotation.Assertions;
import com.facebook.react.views.view.ReactClippingViewGroupHelper;
/**
* Implementation of a {@link DrawCommandManager} with clipping. Performs drawing by iterating
* over an array of DrawCommands, executing them one by one except when the commands are clipped.
* Abstract class for a {@link DrawCommandManager} with directional clipping. Allows support for
* vertical and horizontal clipping by implementing abstract methods.
*
* Uses two dynamic programming arrays to efficiently update which views and commands are onscreen,
* while not having to sort the incoming draw commands. The draw commands are loosely sorted, as
* they represent a flattening of the normal view hierarchy, and we use that information to quickly
* find children that should be considered onscreen. One array keeps track of, for each index, the
* maximum bottom position that occurs at or before that index; the other keeps track of the
* minimum top position that occurs at or after that index. Given the following children:
*
* +---------------------------------+ 0 (Y coordinate)
* | 0 |
* | +-----------+ | 10
* | | 1 | |
* | | | +--------------+ | 20
* | | | | 3 | |
* | +-----------+ | | | 30
* | | | |
* | +-----------+ | | | 40
* | | 2 | | | |
* | | | +--------------+ | 50
* | | | |
* | +-----------+ | 60
* | |
* +---------------------------------+ 70
*
* +-----------+ 80
* | 4 |
* | | +--------------+ 90
* | | | 6 |
* +-----------+ | | 100
* | |
* +-----------+ | | 110
* | 5 | | |
* | | +--------------+ 120
* | |
* +-----------+ 130
*
* The two arrays are:
* 0 1 2 3 4 5 6
* Max Bottom: [70, 70, 70, 70, 100, 130, 130]
* Min Top: [ 0, 0, 0, 0, 80, 90, 90]
*
* We can then binary search for the first max bottom that is below our rect, and the first min top
* that is above our rect.
*
* If the top and bottom of the rect are 55 and 85, respectively, we will start drawing at index 0
* and stop at index 4.
*
* +---------------------------------+ 0 (Y coordinate)
* | 0 |
* | +-----------+ | 10
* | | 1 | |
* | | | +--------------+ | 20
* | | | | 3 | |
* | +-----------+ | | | 30
* | | | |
* | +-----------+ | | | 40
* | | 2 | | | |
* | | | +--------------+ | 50
* - -| -| - - - -| - - - - - - |- - -
* | +-----------+ | 60
* | |
* +---------------------------------+ 70
*
* +-----------+ 80
* - - -| 4 - - - | - - - - - - - - -
* | | +--------------+ 90
* | | | 6 |
* +-----------+ | | 100
* | |
* +-----------+ | | 110
* | 5 | | |
* | | +--------------+ 120
* | |
* +-----------+ 130
*
* If the top and bottom are 75 and 105 respectively, we will start drawing at index 4 and stop at
* index 6.
*
* +---------------------------------+ 0 (Y coordinate)
* | 0 |
* | +-----------+ | 10
* | | 1 | |
* | | | +--------------+ | 20
* | | | | 3 | |
* | +-----------+ | | | 30
* | | | |
* | +-----------+ | | | 40
* | | 2 | | | |
* | | | +--------------+ | 50
* | | | |
* | +-----------+ | 60
* | |
* +---------------------------------+ 70
* - - - - - - - - - - - - - - - -
* +-----------+ 80
* | 4 |
* | | +--------------+ 90
* | | | 6 |
* +-----------+ | | 100
* - - - - - - - |- - - - - | - - -
* +-----------+ | | 110
* | 5 | | |
* | | +--------------+ 120
* | |
* +-----------+ 130
*
* While this doesn't map exactly to all of the commands that could be clipped, it means that
* children which contain other children (a pretty common case when flattening views) are clipped
* or unclipped as one logical unit. This has the side effect of minimizing the amount of
* invalidates coming from minor clipping rect adjustments. The underlying dynamic programming
* arrays can be calculated off the UI thread in O(n) time, requiring just two passes through the
* command array.
*
* We do a similar optimization when searching for matching node regions, as node regions are
* loosely sorted as well when clipping.
*/
/* package */ abstract class ClippingDrawCommandManager extends DrawCommandManager {
private final FlatViewGroup mFlatViewGroup;
@@ -63,6 +178,13 @@ import com.facebook.react.views.view.ReactClippingViewGroupHelper;
initialSetup(drawCommands);
}
/**
* Initially setup this instance. Makes sure the draw commands are mounted, and that our
* clipping rect reflects our current bounds.
*
* @param drawCommands The list of current draw commands. In current implementations, this will
* always be DrawCommand.EMPTY_ARRAY
*/
private void initialSetup(DrawCommand[] drawCommands) {
mountDrawCommands(
drawCommands,
@@ -255,14 +377,18 @@ import com.facebook.react.views.view.ReactClippingViewGroupHelper;
}
}
// Returns true if a view is currently animating.
/**
* Returns true if a view is currently animating.
*/
private static boolean animating(View view) {
Animation animation = view.getAnimation();
return animation != null && !animation.hasEnded();
}
// Return true if a command index is currently onscreen.
boolean withinBounds(int i) {
/**
* Returns true if a command index is currently onscreen.
*/
private boolean withinBounds(int i) {
return mStart <= i && i < mStop;
}
@@ -291,6 +417,22 @@ import com.facebook.react.views.view.ReactClippingViewGroupHelper;
return true;
}
/**
* Used either after we have updated the current rect, or when we have mounted new commands and
* the rect hasn't changed. Updates the clipping after mStart and mStop have been set to the
* correct values. For draw commands, this is all it takes to update the command mounting, as
* draw commands are only attached in a conceptual sense, and rely on the android view
* hierarchy.
*
* For native children, we have to walk through our current views and remove any that are no
* longer on screen, and add those that are newly on screen. As an optimization for fling, if we
* are removing two or more native views we instead detachAllViews from the {@link FlatViewGroup}
* and re-attach or add as needed.
*
* This approximation is roughly correct, as we tend to add and remove the same amount of views,
* and each add and remove pair is O(n); detachAllViews and re-attach requires two passes, so
* using this once we are removing more than two native views is a good breakpoint.
*/
private void updateClippingToCurrentRect() {
for (int i = 0, size = mFlatViewGroup.getChildCount(); i < size; i++) {
View view = mFlatViewGroup.getChildAt(i);
@@ -372,6 +514,47 @@ import com.facebook.react.views.view.ReactClippingViewGroupHelper;
return mClippedSubviews.values();
}
/**
* Draws the unclipped commands on the given canvas. This would be much simpler if we didn't
* have to worry about animating views, as we could simply:
*
* for (int i = start; i < stop; i++) {
* drawCommands[i].draw(...);
* }
*
* This is complicated however by animating views, which may occur before or after the current
* clipping rect. Consider the following array:
*
* +--------------+
* | DrawView | 0
* | *animating* |
* +--------------+
* | DrawCommmand | 1
* | *clipped* |
* +--------------+
* | DrawCommand | 2 start
* | |
* +--------------+
* | DrawCommand | 3
* | |
* +--------------+
* | DrawView | 4
* | |
* +--------------+
* | DrawView | 5 stop
* | *clipped* |
* +--------------+
* | DrawView | 6
* | *animating* |
* +--------------+
*
* 2, 3, and 4 are onscreen according to bounds, while 0 and 6 are onscreen according to
* animation. We have to walk through the attached children making sure to draw any draw
* commands that should be drawn before that draw view, as well as making sure not to draw any
* draw commands that are out of bounds.
*
* @param canvas The canvas to draw on.
*/
@Override
public void draw(Canvas canvas) {
int commandIndex = mStart;