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PONSScrollView constant scrolling (and expansion) with as few drawRect: calls as possible
 

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  1. PONSScrollView constant scrolling (and expansion) with as few drawRect: calls as possible
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    <p>I have an application that records audio and draws the waveform (along with some other elements) on the screen. While recording, I'd like to be drawing the waveform in the containerView of an <code>NSScrollView</code>. The containerView keeps expanding to accomodate the new audio information and keeps scrolling to the end. This behavior is exactly like how the scrollviews in GarageBand act when recording new information.</p> <p>While I've figured out how to accomplish this, my system seems to use an unnecessary number of <code>drawRect:</code> calls when doing the scrolling. What's the most efficient way to do this (update the contentView size, draw the new content on the expanded area, and scroll so the end is visible? Somehow, mine ends up calling drawRect 5 times on each scroll once the containerView is larger width-wise than the scrollView</p> <p>Document view of scroller is set:</p> <p><code>[self.scrollView setDocumentView:self.containerView];</code></p> <p>The method to scroll further (called from an <code>NSTimer</code>):</p> <pre><code>- (void)scrollFurther { scrollPoint = ([SSSubdivisionManager manager].lastStartSample + [RemoteIOPlayer remote].diffInFrames) / (zoomLevel * baseZoomLevel); int scrollWidth = self.scrollView.frame.size.width; CGRect frame = self.containerView.frame; if (scrollPoint &gt;= ((scrollPoint + (scrollWidth * 0.5f) ) / 2)) { if (![SSAudioManager manager].isDoingInputPlayback) { frame.size.width = scrollPoint + (scrollWidth * 0.5f); NSLog(@"Setting scroller frame to: %@", NSStringFromRect(frame)); [self.containerView setFrame:frame]; } NSPoint p = NSMakePoint(scrollPoint - (scrollWidth * 0.5), 0); NSLog(@"Scrolling to point %@", NSStringFromPoint(p)); [self.containerView scrollPoint:p]; } else { NSLog(@"Not exapanding frame or scrolling to a point"); [self.containerView setNeedsDisplayInRect:frame]; } } </code></pre> <p>And the resulting log calls:</p> <p>At first, when the containerView is smaller than the scrollView:</p> <pre><code>2012-07-29 17:42:43.607 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{0, 0}, {1924, 700}} 2012-07-29 17:42:43.683 MET[4679:503] Setting scroller frame to: {{0, 0}, {1942.3199462890625, 700}} 2012-07-29 17:42:43.684 MET[4679:503] Scrolling to point {580.3199462890625, 0} 2012-07-29 17:42:43.687 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{0, 0}, {1942, 700}} 2012-07-29 17:42:43.757 MET[4679:503] Setting scroller frame to: {{0, 0}, {1957.6800537109375, 700}} 2012-07-29 17:42:43.758 MET[4679:503] Scrolling to point {595.6800537109375, 0} 2012-07-29 17:42:43.760 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{0, 0}, {1957, 700}} 2012-07-29 17:42:43.835 MET[4679:503] Setting scroller frame to: {{0, 0}, {1975.5999755859375, 700}} 2012-07-29 17:42:43.836 MET[4679:503] Scrolling to point {613.5999755859375, 0} 2012-07-29 17:42:43.839 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{0, 0}, {1975, 700}} 2012-07-29 17:42:43.889 MET[4679:503] Setting scroller frame to: {{0, 0}, {1988.4000244140625, 700}} 2012-07-29 17:42:43.890 MET[4679:503] Scrolling to point {626.4000244140625, 0} 2012-07-29 17:42:43.892 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{0, 0}, {1988, 700}} </code></pre> <p>And then, it gets out of control:</p> <pre><code>2012-07-29 17:42:43.954 MET[4679:503] Setting scroller frame to: {{0, 0}, {2001.199951171875, 700}} 2012-07-29 17:42:43.956 MET[4679:503] Scrolling to point {639.199951171875, 0} 2012-07-29 17:42:43.960 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{1536, 512}, {465.199951171875, 188}} 2012-07-29 17:42:43.961 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{1024, 512}, {512, 188}} 2012-07-29 17:42:43.964 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{512, 512}, {512, 188}} 2012-07-29 17:42:43.971 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{1536, 0}, {465.199951171875, 512}} 2012-07-29 17:42:43.972 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{1024, 0}, {512, 512}} 2012-07-29 17:42:43.977 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{512, 0}, {512, 512}} 2012-07-29 17:42:44.098 MET[4679:503] Setting scroller frame to: {{0, 0}, {2034.47998046875, 700}} 2012-07-29 17:42:44.099 MET[4679:503] Scrolling to point {672.47998046875, 0} 2012-07-29 17:42:44.104 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{1536, 512}, {498.47998046875, 188}} 2012-07-29 17:42:44.107 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{1024, 512}, {512, 188}} 2012-07-29 17:42:44.112 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{512, 512}, {512, 188}} 2012-07-29 17:42:44.118 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{1536, 0}, {498.47998046875, 512}} 2012-07-29 17:42:44.120 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{1024, 0}, {512, 512}} 2012-07-29 17:42:44.125 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{512, 0}, {512, 512}} 2012-07-29 17:42:44.154 MET[4679:503] Setting scroller frame to: {{0, 0}, {2047.280029296875, 700}} 2012-07-29 17:42:44.155 MET[4679:503] Scrolling to point {685.280029296875, 0} 2012-07-29 17:42:44.157 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{1536, 512}, {511.280029296875, 188}} 2012-07-29 17:42:44.159 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{1024, 512}, {512, 188}} 2012-07-29 17:42:44.162 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{512, 512}, {512, 188}} 2012-07-29 17:42:44.168 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{1536, 0}, {511.280029296875, 512}} 2012-07-29 17:42:44.172 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{1024, 0}, {512, 512}} 2012-07-29 17:42:44.178 MET[4679:503] -[SSVisualContainer drawRect:] [Line 70] Drawrect: {{512, 0}, {512, 512}} </code></pre>
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    1. COthis isn't really out of control. notice that each of the individual drawRect calls in the beginning cover your entire screen area, whereas the later drawRect calls each only cover a much smaller portion of your screen area, and none of which overlap. these six calls are thus actually **more** efficient than a single call to redraw the whole area (if you buy the assumption that a drawRect on a {100,100} area will take 25% as much time as a drawRect on a {200,200} area).
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    2. COYes, but it redraws back to point 0 each time -- I only need drawing calls on the area added by the new setFrame call.
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    3. COi guess the way i'm reading the logs, it never draws anything to the left of 512 in the second set you presented. it might not be completely optimized, but from what i can tell, those later drawRect calls are only on small portions of your screen (the first 3 are 512x188, the next three are 512x512), and altogether, it never redraws anything on the left portion of your screen.
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