From ff4c3855aa5eba7de25ecb5cca77886b4039b6d9 Mon Sep 17 00:00:00 2001
From: Tor Andersson <tor.andersson@artifex.com>
Date: Tue, 1 Nov 2011 03:55:43 +0100
Subject: Fix scrolling/page flipping glitches by using real animations.

The UIScrollView animated scrolling doesn't interact with the regular
animation framework, nor does it work well with gesture recognizers.
When tapping quickly to flip pages, the repeated taps overwrite the
animations already started. Fix this by queuing real animations instead.
---
 ios/main.m | 58 +++++++++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 43 insertions(+), 15 deletions(-)

(limited to 'ios')

diff --git a/ios/main.m b/ios/main.m
index bfcfc805..03601ba7 100644
--- a/ios/main.m
+++ b/ios/main.m
@@ -44,6 +44,7 @@ static UIBarButtonItem *flexibleSpace = nil;
 	int width; // current screen size
 	int height;
 	int current; // currently visible page
+	int scroll_animating; // stop view updates during scrolling animations
 }
 - (id) initWithFile: (NSString*)filename;
 - (void) loadPage: (int)number;
@@ -392,9 +393,12 @@ static UIImage *renderPage(pdf_xref *xref, int number, float width, float height
 	[canvas setPagingEnabled: YES];
 	[canvas setShowsHorizontalScrollIndicator: NO];
 	[canvas setShowsVerticalScrollIndicator: NO];
-	[canvas addGestureRecognizer: [[UITapGestureRecognizer alloc] initWithTarget: self action: @selector(didSingleTap:)]];
 	[canvas setDelegate: self];
 
+	[canvas addGestureRecognizer: [[UITapGestureRecognizer alloc] initWithTarget: self action: @selector(didSingleTap:)]];
+
+	scroll_animating = NO;
+
 	indicator = [[UILabel alloc] initWithFrame: CGRectZero];
 	[indicator setAutoresizingMask: UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleRightMargin | UIViewAutoresizingFlexibleTopMargin];
 	[indicator setText: @"0000 of 9999"];
@@ -459,6 +463,7 @@ static UIImage *renderPage(pdf_xref *xref, int number, float width, float height
 	});
 
 	free(pageviews);
+
 	[indicator release];
 	[slider release];
 	[wrapper release];
@@ -507,6 +512,8 @@ static UIImage *renderPage(pdf_xref *xref, int number, float width, float height
 				}
 				[image release];
 			});
+		} else {
+			printf("not loading page %d\n", number);
 		}
 	});
 }
@@ -593,25 +600,21 @@ static UIImage *renderPage(pdf_xref *xref, int number, float width, float height
 	if (width == 0)
 		return; // not visible yet
 
+	if (scroll_animating)
+		return; // don't mess with layout during animations
+
 	float x = [canvas contentOffset].x + width * 0.5f;
 	current = x / width;
 
-#if 0
-	for (int i = 0; i < pdf_count_pages(xref); i++)
-		if (i != current)
-			[self unloadPage: i];
-	[self loadPage: current];
-#else
 	for (int i = 0; i < pdf_count_pages(xref); i++)
 		if (i < current - 2 || i > current + 2)
 			[self unloadPage: i];
 	[self loadPage: current];
 	[self loadPage: current + 1];
 	[self loadPage: current - 1];
-#endif
 
 	[indicator setText: [NSString stringWithFormat: @" %d of %d ", current+1, pdf_count_pages(xref)]];
-	[slider setValue: current animated: YES];
+	[slider setValue: current];
 }
 
 - (void) gotoPage: (int)number animated: (BOOL)animated
@@ -620,8 +623,33 @@ static UIImage *renderPage(pdf_xref *xref, int number, float width, float height
 		number = 0;
 	if (number >= pdf_count_pages(xref))
 		number = pdf_count_pages(xref) - 1;
+	if (animated) {
+		// setContentOffset:animated: does not use the normal animation
+		// framework. It also doesn't play nice with the tap gesture
+		// recognizer. So we do our own page flipping animation here.
+		// We must set the scroll_animating flag so that we don't create
+		// or remove subviews until after the animation, or they'll
+		// swoop in from origo during the animation.
+		scroll_animating = YES;
+		[UIView beginAnimations: @"MuScroll" context: NULL];
+		[UIView setAnimationDuration: 0.4];
+		[UIView setAnimationBeginsFromCurrentState: YES];
+		[UIView setAnimationDelegate: self];
+		[UIView setAnimationDidStopSelector: @selector(didGotoPage)];
+		[canvas setContentOffset: CGPointMake(number * width, 0)];
+		[slider setValue: number];
+		[indicator setText: [NSString stringWithFormat: @" %d of %d ", number+1, pdf_count_pages(xref)]];
+		[UIView commitAnimations];
+	} else {
+		[canvas setContentOffset: CGPointMake(number * width, 0)];
+	}
 	current = number;
-	[canvas setContentOffset: CGPointMake(current * width, 0) animated: animated];
+}
+
+- (void) didGotoPage
+{
+	scroll_animating = NO;
+	[self scrollViewDidScroll: canvas];
 }
 
 - (BOOL) shouldAutorotateToInterfaceOrientation: (UIInterfaceOrientation)o
@@ -664,11 +692,11 @@ static UIImage *renderPage(pdf_xref *xref, int number, float width, float height
 	float x1 = (width - GAP) - x0;
 	p.x -= ofs.x;
 	p.y -= ofs.y;
-	if (p.x < x0)
-		[self gotoPage: current - 1 animated: YES];
-	else if (p.x > x1)
-		[self gotoPage: current + 1 animated: YES];
-	else {
+	if (p.x < x0) {
+		[self gotoPage: current-1 animated: YES];
+	} else if (p.x > x1) {
+		[self gotoPage: current+1 animated: YES];
+	} else {
 		if ([[self navigationController] isNavigationBarHidden])
 			[self showNavigationBar];
 		else
-- 
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