# HG changeset patch
# User Chris Cannam
# Date 1537527005 -3600
# Node ID c1f719094c251b2b3219ce8601f09fc58b59f97d
# Parent  344f29e46258eeed8039b74398c909558ba41c6c
Ensure getFrameForX returns value on zoom blocksize boundary; take advantage of that (this is essentially reverting to the same behaviour as in the default branch, which we should probably have done all along)

diff -r 344f29e46258 -r c1f719094c25 layer/Colour3DPlotRenderer.cpp
--- a/layer/Colour3DPlotRenderer.cpp	Thu Sep 20 15:42:12 2018 +0100
+++ b/layer/Colour3DPlotRenderer.cpp	Fri Sep 21 11:50:05 2018 +0100
@@ -764,14 +764,14 @@
     int drawBufferWidth;
     int binResolution = model->getResolution();
 
-    int limitOverrun = 100; // overrun from edge before we decide this
-                            // isn't going to work out
-    int leftLimit = -limitOverrun;
-    int rightLimit = v->getPaintWidth() + limitOverrun;
+    // These loops should eventually terminate provided that
+    // getFrameForX always returns a multiple of the zoom level,
+    // i.e. there is some x for which getFrameForX(x) == 0 and
+    // subsequent return values are equally spaced
     
-    for (int x = x0; x > leftLimit; --x) {
+    for (int x = x0; ; --x) {
         sv_frame_t f = v->getFrameForX(x);
-        if ((f / binResolution) * binResolution == f || x-1 == leftLimit) {
+        if ((f / binResolution) * binResolution == f) {
             if (leftCropFrame == -1) leftCropFrame = f;
             else if (x < x0 - 2) {
                 leftBoundaryFrame = f;
@@ -780,9 +780,9 @@
         }
     }
     
-    for (int x = x0 + repaintWidth; x < rightLimit; ++x) {
+    for (int x = x0 + repaintWidth; ; ++x) {
         sv_frame_t f = v->getFrameForX(x);
-        if ((f / binResolution) * binResolution == f || x+1 == rightLimit) {
+        if ((f / binResolution) * binResolution == f) {
             if (rightCropFrame == -1) rightCropFrame = f;
             else if (x > x0 + repaintWidth + 2) {
                 rightBoundaryFrame = f;
@@ -791,11 +791,6 @@
         }
     }
 
-    if (leftBoundaryFrame == -1 || rightBoundaryFrame == -1) {
-        SVCERR << "WARNING: failed to set left or right boundary frame (values are " << leftBoundaryFrame << " and " << rightBoundaryFrame << " respectively)" << endl;
-        return;
-    }
-    
     drawBufferWidth = int
         ((rightBoundaryFrame - leftBoundaryFrame) / binResolution);
     
diff -r 344f29e46258 -r c1f719094c25 view/View.cpp
--- a/view/View.cpp	Thu Sep 20 15:42:12 2018 +0100
+++ b/view/View.cpp	Fri Sep 21 11:50:05 2018 +0100
@@ -395,16 +395,33 @@
 sv_frame_t
 View::getFrameForX(int x) const
 {
+    // Note, this must always return a value that is on a zoom-level
+    // boundary - regardless of whether the nominal centre frame is on
+    // such a boundary or not
+
     int diff = x - (width()/2);
-    sv_frame_t fdiff = diff;
-
+    sv_frame_t level = m_zoomLevel.level;
+    sv_frame_t fdiff, result;
+    
     if (m_zoomLevel.zone == ZoomLevel::FramesPerPixel) {
-        fdiff *= m_zoomLevel.level;
+        fdiff = diff * level;
+        result = ((fdiff + m_centreFrame) / level) * level;
     } else {
-        fdiff /= m_zoomLevel.level;
+        fdiff = diff / level;
+        result = fdiff + m_centreFrame;
     }
-
-    return fdiff + m_centreFrame;
+/*    
+    if (x == 0) {
+        SVCERR << "getFrameForX(" << x << "): diff = " << diff << ", fdiff = "
+               << fdiff << ", m_centreFrame = " << m_centreFrame
+               << ", level = " << m_zoomLevel.level
+               << ", diff % level = " << (diff % m_zoomLevel.level)
+               << ", nominal " << fdiff + m_centreFrame
+               << ", will return " << result
+               << endl;
+    }
+*/        
+    return result;
 }
 
 double