attempt to correctly respond to changes in _amplitude_above_axis in ArdourCanvas...
[ardour.git] / libs / canvas / wave_view.cc
index a756cfe430a1547ff9c414ac9d7144bc7694f419..f4e56cb1d53f6fb2af75ca26a69276fdd9293efc 100644 (file)
 #include "ardour/lmath.h"
 #include "ardour/audioregion.h"
 #include "ardour/audiosource.h"
+#include "ardour/session.h"
 
-#include "canvas/wave_view.h"
-#include "canvas/utils.h"
 #include "canvas/canvas.h"
 #include "canvas/colors.h"
+#include "canvas/debug.h"
+#include "canvas/utils.h"
+#include "canvas/wave_view.h"
+
+#include "evoral/Range.hpp"
 
 #include <gdkmm/general.h>
 
@@ -49,6 +53,7 @@
 
 using namespace std;
 using namespace ARDOUR;
+using namespace PBD;
 using namespace ArdourCanvas;
 
 double WaveView::_global_gradient_depth = 0.6;
@@ -87,12 +92,17 @@ WaveView::WaveView (Canvas* c, boost::shared_ptr<ARDOUR::AudioRegion> region)
        , _start_shift (0.0)
        , _region_start (region->start())
        , get_image_in_thread (false)
+       , always_get_image_in_thread (false)
        , rendered (false)
 {
+       if (!images) {
+               images = new WaveViewCache;
+       }
+
        VisualPropertiesChanged.connect_same_thread (invalidation_connection, boost::bind (&WaveView::handle_visual_property_change, this));
        ClipLevelChanged.connect_same_thread (invalidation_connection, boost::bind (&WaveView::handle_clip_level_change, this));
 
-       ImageReady.connect (image_ready_connection, MISSING_INVALIDATOR, boost::bind (&WaveView::image_ready, this), gui_context());
+       ImageReady.connect (image_ready_connection, invalidator (*this), boost::bind (&WaveView::image_ready, this), gui_context());
 }
 
 WaveView::WaveView (Item* parent, boost::shared_ptr<ARDOUR::AudioRegion> region)
@@ -112,14 +122,20 @@ WaveView::WaveView (Item* parent, boost::shared_ptr<ARDOUR::AudioRegion> region)
        , _gradient_depth_independent (false)
        , _amplitude_above_axis (1.0)
        , _region_amplitude (region->scale_amplitude ())
+       , _start_shift (0.0)
        , _region_start (region->start())
        , get_image_in_thread (false)
+       , always_get_image_in_thread (false)
        , rendered (false)
 {
+       if (!images) {
+               images = new WaveViewCache;
+       }
+
        VisualPropertiesChanged.connect_same_thread (invalidation_connection, boost::bind (&WaveView::handle_visual_property_change, this));
        ClipLevelChanged.connect_same_thread (invalidation_connection, boost::bind (&WaveView::handle_clip_level_change, this));
 
-       ImageReady.connect (image_ready_connection, MISSING_INVALIDATOR, boost::bind (&WaveView::image_ready, this), gui_context());
+       ImageReady.connect (image_ready_connection, invalidator (*this), boost::bind (&WaveView::image_ready, this), gui_context());
 }
 
 WaveView::~WaveView ()
@@ -136,9 +152,16 @@ WaveView::debug_name() const
 void
 WaveView::image_ready ()
 {
+        DEBUG_TRACE (DEBUG::WaveView, string_compose ("queue draw for %1 at %2 (vis = %3 CR %4)\n", this, g_get_monotonic_time(), visible(), current_request));
        redraw ();
 }
 
+void
+WaveView::set_always_get_image_in_thread (bool yn)
+{
+       always_get_image_in_thread = yn;
+}
+
 void
 WaveView::handle_visual_property_change ()
 {
@@ -235,45 +258,71 @@ WaveView::set_clip_level (double dB)
 void
 WaveView::invalidate_image_cache ()
 {
+        DEBUG_TRACE (DEBUG::WaveView, string_compose ("%1 invalidates image cache and cancels current request\n", this));
        cancel_my_render_request ();
        _current_image.reset ();
 }
 
-Coord
-WaveView::y_extent (double s, bool /*round_to_lower_edge*/) const
+void
+WaveView::compute_tips (PeakData const & peak, WaveView::LineTips& tips) const
 {
-       /* it is important that this returns an integral value, so that we
-        * can ensure correct single pixel behaviour.
-        *
-        * we need (_height - max(wave_line_width))
-        * wave_line_width == 1 IFF top==bottom (1 sample per pixel or flat line)
-        * wave_line_width == 2 otherwise
-        * then round away from the zero line, towards peak
-        */
-       if (_shape == Rectified) {
-               // we only ever have 1 point and align to the bottom (not center)
-               return floor ((1.0 - s) * (_height - 2.0));
-       } else {
-               /* currently canvas rectangle is off-by-one and we
-                * cannot draw a pixel at 0 (-.5 .. +.5) without it being
-                * clipped. A value 1.0 (ideally one point at y=0) ends
-                * up a pixel down. and a value of -1.0 (ideally y = _height-1)
-                * currently is on the bottom separator line :(
-                * So to make the complete waveform appear centered in
-                * a region, we translate by +.5 (instead of -.5)
-                * and waste two pixel of height: -4 (instad of -2)
-                *
-                * This needs fixing in canvas/rectangle the intersect
-                * functions and probably a couple of other places as well...
+       const double effective_height  = _height;
+
+       /* remember: canvas (and cairo) coordinate space puts the origin at the upper left. 
+          
+          So, a sample value of 1.0 (0dbFS) will be computed as:
+
+                (1.0 - 1.0) * 0.5 * effective_height
+
+          which evaluates to 0, or the top of the image.
+
+          A sample value of -1.0 will be computed as
+
+               (1.0 + 1.0) * 0.5 * effective height
+
+           which evaluates to effective height, or the bottom of the image.
+       */
+
+       const double pmax = (1.0 - peak.max) * 0.5 * effective_height;
+       const double pmin = (1.0 - peak.min) * 0.5 * effective_height;
+
+       /* remember that the bottom of the image (pmin) has larger y-coordinates
+          than the top (pmax).
+       */
+
+       double spread = (pmin - pmax) * 0.5;
+
+       /* find the nearest pixel to the nominal center. */
+       const double center = round (pmin - spread);
+
+       if (spread < 1.0) {
+               /* minimum distance between line ends is 1 pixel, and we want it "centered" on a pixel,
+                  as per cairo single-pixel line issues.
+
+                  NOTE: the caller will not draw a line between these two points if the spread is
+                  less than 2 pixels. So only the tips.top value matters, which is where we will
+                  draw a single pixel as part of the outline.
                 */
-               Coord pos;
-               if (s < 0) {
-                       pos = ceil  ((1.0 - s) * .5 * (_height - 4.0));
-               } else {
-                       pos = floor ((1.0 - s) * .5 * (_height - 4.0));
-               }
-               return min (_height - 4.0, (max (0.0, pos)));
+               tips.top = center;
+               tips.bot = center + 1.0;
+       } else {
+               /* round spread above and below center to an integer number of pixels */
+               spread = round (spread);
+               /* top and bottom are located equally either side of the center */
+               tips.top = center - spread;
+               tips.bot = center + spread;
        }
+       
+       tips.top = min (effective_height, max (0.0, tips.top));
+       tips.bot = min (effective_height, max (0.0, tips.bot));
+}
+       
+
+Coord
+WaveView::y_extent (double s) const
+{
+       assert (_shape == Rectified);
+       return floor ((1.0 - s) * _height);
 }
 
 void
@@ -308,16 +357,6 @@ WaveView::draw_absent_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData
        context->fill ();
 }
 
-struct LineTips {
-       double top;
-       double bot;
-       double spread;
-       bool clip_max;
-       bool clip_min;
-
-       LineTips() : top (0.0), bot (0.0), clip_max (false), clip_min (false) {}
-};
-
 struct ImageSet {
        Cairo::RefPtr<Cairo::ImageSurface> wave;
        Cairo::RefPtr<Cairo::ImageSurface> outline;
@@ -360,7 +399,7 @@ WaveView::draw_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peak
           has been scaled by scale_amplitude() already.
        */
 
-       const double clip_level = _clip_level * _region_amplitude;
+       const double clip_level = _clip_level * req->amplitude;
 
        if (_shape == WaveView::Rectified) {
 
@@ -374,8 +413,8 @@ WaveView::draw_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peak
 
                                tips[i].bot = height() - 1.0;
                                const double p = alt_log_meter (fast_coefficient_to_dB (max (fabs (_peaks[i].max), fabs (_peaks[i].min))));
-                               tips[i].top = y_extent (p, false);
-                               tips[i].spread = p * (_height - 1.0);
+                               tips[i].top = y_extent (p);
+                               tips[i].spread = p * _height;
 
                                if (_peaks[i].max >= clip_level) {
                                        tips[i].clip_max = true;
@@ -391,8 +430,8 @@ WaveView::draw_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peak
 
                                tips[i].bot = height() - 1.0;
                                const double p = max(fabs (_peaks[i].max), fabs (_peaks[i].min));
-                               tips[i].top = y_extent (p, false);
-                               tips[i].spread = p * (_height - 2.0);
+                               tips[i].top = y_extent (p);
+                               tips[i].spread = p * _height;
                                if (p >= clip_level) {
                                        tips[i].clip_max = true;
                                }
@@ -404,34 +443,34 @@ WaveView::draw_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peak
 
                if (_logscaled) {
                        for (int i = 0; i < n_peaks; ++i) {
-                               double top = _peaks[i].max;
-                               double bot = _peaks[i].min;
+                               PeakData p;
+                               p.max = _peaks[i].max;
+                               p.min = _peaks[i].min;
 
                                if (_peaks[i].max >= clip_level) {
-                                               tips[i].clip_max = true;
+                                       tips[i].clip_max = true;
                                }
                                if (-(_peaks[i].min) >= clip_level) {
                                        tips[i].clip_min = true;
                                }
 
-                               if (top > 0.0) {
-                                       top = alt_log_meter (fast_coefficient_to_dB (top));
-                               } else if (top < 0.0) {
-                                       top =-alt_log_meter (fast_coefficient_to_dB (-top));
+                               if (p.max > 0.0) {
+                                       p.max = alt_log_meter (fast_coefficient_to_dB (p.max));
+                               } else if (p.max < 0.0) {
+                                       p.max =-alt_log_meter (fast_coefficient_to_dB (-p.max));
                                } else {
-                                       top = 0.0;
+                                       p.max = 0.0;
                                }
 
-                               if (bot > 0.0) {
-                                       bot = alt_log_meter (fast_coefficient_to_dB (bot));
-                               } else if (bot < 0.0) {
-                                       bot = -alt_log_meter (fast_coefficient_to_dB (-bot));
+                               if (p.min > 0.0) {
+                                       p.min = alt_log_meter (fast_coefficient_to_dB (p.min));
+                               } else if (p.min < 0.0) {
+                                       p.min = -alt_log_meter (fast_coefficient_to_dB (-p.min));
                                } else {
-                                       bot = 0.0;
+                                       p.min = 0.0;
                                }
-
-                               tips[i].top = y_extent (top, false);
-                               tips[i].bot = y_extent (bot, true);
+                               
+                               compute_tips (p, tips[i]);
                                tips[i].spread = tips[i].bot - tips[i].top;
                        }
 
@@ -444,8 +483,7 @@ WaveView::draw_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peak
                                        tips[i].clip_min = true;
                                }
 
-                               tips[i].top = y_extent (_peaks[i].max, false);
-                               tips[i].bot = y_extent (_peaks[i].min, true);
+                               compute_tips (_peaks[i], tips[i]);
                                tips[i].spread = tips[i].bot - tips[i].top;
                        }
 
@@ -466,16 +504,16 @@ WaveView::draw_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peak
        /* ensure single-pixel lines */
 
        wave_context->set_line_width (1.0);
-       wave_context->translate (0.5, +1.5);
+       wave_context->translate (0.5, 0.5);
 
        outline_context->set_line_width (1.0);
-       outline_context->translate (0.5, +1.5);
+       outline_context->translate (0.5, 0.5);
 
        clip_context->set_line_width (1.0);
-       clip_context->translate (0.5, +1.5);
+       clip_context->translate (0.5, 0.5);
 
        zero_context->set_line_width (1.0);
-       zero_context->translate (0.5, +1.5);
+       zero_context->translate (0.5, 0.5);
 
        /* the height of the clip-indicator should be at most 7 pixels,
         * or 5% of the height of the waveview item.
@@ -537,7 +575,7 @@ WaveView::draw_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peak
                outline_context->stroke ();
 
        } else {
-               const double height_2 = (_height - 2.5) * .5;
+               const int height_zero = floor( _height * .5);
 
                for (int i = 0; i < n_peaks; ++i) {
 
@@ -547,6 +585,7 @@ WaveView::draw_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peak
                                wave_context->move_to (i, tips[i].top);
                                wave_context->line_to (i, tips[i].bot);
                        }
+                       
                        /* draw square waves and other discontiguous points clearly */
                        if (i > 0) {
                                if (tips[i-1].top + 2 < tips[i].top) {
@@ -562,10 +601,11 @@ WaveView::draw_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peak
                                }
                        }
 
-                       /* zero line */
+                       /* zero line, show only if there is enough spread 
+                       or the waveform line does not cross zero line */
 
-                       if (tips[i].spread >= 5.0 && show_zero_line()) {
-                               zero_context->move_to (i, floor(height_2));
+                       if (show_zero_line() && ((tips[i].spread >= 5.0) || (tips[i].top > height_zero ) || (tips[i].bot < height_zero)) ) {
+                               zero_context->move_to (i, height_zero);
                                zero_context->rel_line_to (1.0, 0);
                        }
 
@@ -586,13 +626,17 @@ WaveView::draw_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peak
                                        clipped = true;
                                }
 
-                               if (!clipped) {
-                                       outline_context->move_to (i, tips[i].bot + 1.0);
-                                       /* normal lower terminal dot */
+                               if (!clipped && tips[i].spread > 2.0) {
+                                       /* only draw the outline if the spread
+                                          implies 3 or more pixels (so that we see 1
+                                          white pixel in the middle).
+                                       */
+                                       outline_context->move_to (i, tips[i].bot);
+                                       /* normal lower terminal dot; line moves up */
                                        outline_context->rel_line_to (0, -1.0);
 
-                                       outline_context->move_to (i, tips[i].top - 1.0);
-                                       /* normal upper terminal dot */
+                                       outline_context->move_to (i, tips[i].top);
+                                       /* normal upper terminal dot, line moves down */
                                        outline_context->rel_line_to (0, 1.0);
                                }
                        } else {
@@ -606,10 +650,15 @@ WaveView::draw_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peak
                                }
 
                                if (!clipped) {
+                                       /* special case where only 1 pixel of
+                                        * the waveform line is drawn (and
+                                        * nothing else).
+                                        *
+                                        * we draw a 1px "line", pretending
+                                        * that the span is 1.0 (whether it is
+                                        * zero or 1.0)
+                                        */
                                        wave_context->move_to (i, tips[i].top);
-                                       /* special case where outline only is drawn.
-                                        * we draw a 1px "line", pretending that the span is 1.0
-                                       */
                                        wave_context->rel_line_to (0, 1.0);
                                }
                        }
@@ -688,18 +737,15 @@ WaveView::draw_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peak
 boost::shared_ptr<WaveViewCache::Entry>
 WaveView::cache_request_result (boost::shared_ptr<WaveViewThreadRequest> req) const
 {
+       
        boost::shared_ptr<WaveViewCache::Entry> ret (new WaveViewCache::Entry (req->channel,
                                                                               req->height,
-                                                                              req->region_amplitude,
+                                                                              req->amplitude,
                                                                               req->fill_color,
                                                                               req->samples_per_pixel,
                                                                               req->start,
                                                                               req->end,
                                                                               req->image));
-       if (!images) {
-               images = new WaveViewCache;
-       }
-
        images->add (_region->audio_source (_channel), ret);
        
        /* consolidate cache first (removes fully-contained
@@ -707,21 +753,26 @@ WaveView::cache_request_result (boost::shared_ptr<WaveViewThreadRequest> req) co
         */
        
        images->consolidate_image_cache (_region->audio_source (_channel),
-                                        _channel, _height, _region_amplitude,
-                                        _fill_color, _samples_per_pixel);
+                                        req->channel, req->height, req->amplitude,
+                                        req->fill_color, req->samples_per_pixel);
 
        return ret;
 }
 
 boost::shared_ptr<WaveViewCache::Entry>
-WaveView::get_image (framepos_t start, framepos_t end) const
+WaveView::get_image (framepos_t start, framepos_t end, bool& full_image) const
 {
        boost::shared_ptr<WaveViewCache::Entry> ret;
+
+       full_image = true;
        
        /* this is called from a ::render() call, when we need an image to
           draw with.
        */
 
+       DEBUG_TRACE (DEBUG::WaveView, string_compose ("%1 needs image from %2 .. %3\n", name, start, end));
+       
+       
        {
                Glib::Threads::Mutex::Lock lmq (request_queue_lock);
 
@@ -729,6 +780,10 @@ WaveView::get_image (framepos_t start, framepos_t end) const
                 * have an image there. if so, use it (and put it in the cache
                 * while we're here.
                 */
+
+                DEBUG_TRACE (DEBUG::WaveView, string_compose ("%1 CR %2 stop? %3 image %4\n", this, current_request, 
+                                                              (current_request ? current_request->should_stop() : false), 
+                                                              (current_request ? current_request->image : 0)));
                
                if (current_request && !current_request->should_stop() && current_request->image) {
 
@@ -740,7 +795,7 @@ WaveView::get_image (framepos_t start, framepos_t end) const
                                
                                ret.reset (new WaveViewCache::Entry (current_request->channel,
                                                                     current_request->height,
-                                                                    current_request->region_amplitude,
+                                                                    current_request->amplitude,
                                                                     current_request->fill_color,
                                                                     current_request->samples_per_pixel,
                                                                     current_request->start,
@@ -748,6 +803,8 @@ WaveView::get_image (framepos_t start, framepos_t end) const
                                                                     current_request->image));
        
                                cache_request_result (current_request);
+                               DEBUG_TRACE (DEBUG::WaveView, string_compose ("%1: got image from completed request, spans %2..%3\n",
+                                                                             name, current_request->start, current_request->end));
                        }
 
                        /* drop our handle on the current request */
@@ -759,14 +816,20 @@ WaveView::get_image (framepos_t start, framepos_t end) const
 
                /* no current image draw request, so look in the cache */
                
-               ret = get_image_from_cache (start, end);
+               ret = get_image_from_cache (start, end, full_image);
+               DEBUG_TRACE (DEBUG::WaveView, string_compose ("%1: lookup from cache gave %2 (full %3)\n",
+                                                             name, ret, full_image));
 
        }
 
-       if (!ret) {
-
-               if (get_image_in_thread) {
+       
+       
+       if (!ret || !full_image) {
 
+               if ((rendered && get_image_in_thread) || always_get_image_in_thread) {
+                        
+                       DEBUG_TRACE (DEBUG::WaveView, string_compose ("%1: generating image in caller thread\n", name));
+                       
                        boost::shared_ptr<WaveViewThreadRequest> req (new WaveViewThreadRequest);
 
                        req->type = WaveViewThreadRequest::Draw;
@@ -775,10 +838,10 @@ WaveView::get_image (framepos_t start, framepos_t end) const
                        req->samples_per_pixel = _samples_per_pixel;
                        req->region = _region; /* weak ptr, to avoid storing a reference in the request queue */
                        req->channel = _channel;
-                       req->width = _canvas->visible_area().width();
                        req->height = _height;
                        req->fill_color = _fill_color;
-                       req->region_amplitude = _region_amplitude;
+                       req->amplitude = _region_amplitude * _amplitude_above_axis;
+                        req->width = desired_image_width ();
 
                        /* draw image in this (the GUI thread) */
                        
@@ -799,19 +862,44 @@ WaveView::get_image (framepos_t start, framepos_t end) const
                }
        }
 
-       
+       if (ret) {
+               DEBUG_TRACE (DEBUG::WaveView, string_compose ("%1 got an image from %2 .. %3 (full ? %4)\n", name, ret->start, ret->end, full_image));
+       } else {
+               DEBUG_TRACE (DEBUG::WaveView, string_compose ("%1 no useful image available\n", name));
+       }
+
        return ret;
 }
 
 boost::shared_ptr<WaveViewCache::Entry>
-WaveView::get_image_from_cache (framepos_t start, framepos_t end) const
+WaveView::get_image_from_cache (framepos_t start, framepos_t end, bool& full) const
 {
        if (!images) {
                return boost::shared_ptr<WaveViewCache::Entry>();
        }
 
        return images->lookup_image (_region->audio_source (_channel), start, end, _channel,
-                                    _height, _region_amplitude, _fill_color, _samples_per_pixel);
+                                    _height, _region_amplitude * _amplitude_above_axis, _fill_color, _samples_per_pixel, full);
+}
+
+framecnt_t
+WaveView::desired_image_width () const
+{
+        /* compute how wide the image should be, in samples. 
+         *
+         * We want at least 1 canvas width's worth, but if that 
+         * represents less than 1/10th of a second, use 1/10th of
+         * a second instead.
+         */
+        
+        framecnt_t canvas_width_samples = _canvas->visible_area().width() * _samples_per_pixel;
+        const framecnt_t one_tenth_of_second = _region->session().frame_rate() / 10;
+
+        if (canvas_width_samples > one_tenth_of_second) {
+                return  canvas_width_samples;
+        } 
+
+        return one_tenth_of_second;
 }
 
 void
@@ -825,12 +913,35 @@ WaveView::queue_get_image (boost::shared_ptr<const ARDOUR::Region> region, frame
        req->samples_per_pixel = _samples_per_pixel;
        req->region = _region; /* weak ptr, to avoid storing a reference in the request queue */
        req->channel = _channel;
-       req->width = _canvas->visible_area().width();
        req->height = _height;
        req->fill_color = _fill_color;
-       req->region_amplitude = _region_amplitude;
+       req->amplitude = _region_amplitude * _amplitude_above_axis;
+        req->width = desired_image_width ();
+
+       if (current_request) {
+               /* this will stop rendering in progress (which might otherwise
+                  be long lived) for any current request.
+               */
+               current_request->cancel ();
+       }
+
+       start_drawing_thread ();
+
+       /* swap requests (protected by lock) */
+
+       {
+               Glib::Threads::Mutex::Lock lm (request_queue_lock);
+               current_request = req;
+
+                DEBUG_TRACE (DEBUG::WaveView, string_compose ("%1 now has current request %2\n", this, req));
 
-       send_request (req);
+                if (request_queue.insert (this).second) {
+                        /* this waveview was not already in the request queue, make sure we wake
+                           the rendering thread in case it is asleep.
+                        */
+                        request_cond.signal ();
+                }
+       }
 }
 
 void
@@ -839,11 +950,13 @@ WaveView::generate_image (boost::shared_ptr<WaveViewThreadRequest> req, bool in_
        if (!req->should_stop()) {
 
                /* sample position is canonical here, and we want to generate
-                * an image that spans about twice the canvas width
+                * an image that spans about 3x the canvas width. We get to that 
+                 * width by using an image sample count of the screen width added
+                 * on each side of the desired image center.
                 */
                
                const framepos_t center = req->start + ((req->end - req->start) / 2);
-               const framecnt_t image_samples = req->width * req->samples_per_pixel; /* one canvas width */
+               const framecnt_t image_samples = req->width;
                
                /* we can request data from anywhere in the Source, between 0 and its length
                 */
@@ -864,8 +977,6 @@ WaveView::generate_image (boost::shared_ptr<WaveViewThreadRequest> req, bool in_
                                                             req->channel,
                                                             req->samples_per_pixel);
                
-               // apply waveform amplitude zoom multiplier
-
                req->image = Cairo::ImageSurface::create (Cairo::FORMAT_ARGB32, n_peaks, req->height);
                /* make sure we record the sample positions that were actually used */
                req->start = sample_start;
@@ -873,9 +984,17 @@ WaveView::generate_image (boost::shared_ptr<WaveViewThreadRequest> req, bool in_
                
                if (peaks_read > 0) {
 
-                       for (framecnt_t i = 0; i < n_peaks; ++i) {
-                               peaks[i].max *= _amplitude_above_axis;
-                               peaks[i].min *= _amplitude_above_axis;
+                       /* region amplitude will have been used to generate the
+                        * peak values already, but not the visual-only
+                        * amplitude_above_axis. So apply that here before
+                        * rendering.
+                        */
+                       
+                       if (_amplitude_above_axis != 1.0) {
+                               for (framecnt_t i = 0; i < n_peaks; ++i) {
+                                       peaks[i].max *= _amplitude_above_axis;
+                                       peaks[i].min *= _amplitude_above_axis;
+                               }
                        }
 
                        draw_image (req->image, peaks.get(), n_peaks, req);
@@ -885,6 +1004,7 @@ WaveView::generate_image (boost::shared_ptr<WaveViewThreadRequest> req, bool in_
        }
        
        if (in_render_thread && !req->should_stop()) {
+                DEBUG_TRACE (DEBUG::WaveView, string_compose ("done with request for %1 at %2 CR %3 req %4 range %5 .. %6\n", this, g_get_monotonic_time(), current_request, req, req->start, req->end));
                const_cast<WaveView*>(this)->ImageReady (); /* emit signal */
        }
        
@@ -909,17 +1029,13 @@ void
 WaveView::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) const
 {
        assert (_samples_per_pixel != 0);
-
-       if (!rendered) {
-               /* first image generation should happen in RENDER thread */
-               get_image_in_thread = false;
-               rendered = true; /* comments in header file */
-       }
        
        if (!_region) {
                return;
        }
 
+        DEBUG_TRACE (DEBUG::WaveView, string_compose ("render %1 at %2\n", this, g_get_monotonic_time()));
+
        /* a WaveView is intimately connected to an AudioRegion. It will
         * display the waveform within the region, anywhere from the start of
         * the region to its end.
@@ -940,6 +1056,8 @@ WaveView::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) cons
        
        Rect self = item_to_window (Rect (0.0, 0.0, region_length() / _samples_per_pixel, _height));
 
+       // cerr << name << " RENDER " << area << " self = " << self << endl;
+       
        /* Now lets get the intersection with the area we've been asked to draw */
 
        boost::optional<Rect> d = self.intersection (area);
@@ -974,7 +1092,7 @@ WaveView::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) cons
        const framepos_t image_end = window_to_image (self.x0, draw_end);
        
        // cerr << "Image/WV space: " << image_start << " .. " << image_end << endl;
-
+       
        /* sample coordinates - note, these are not subject to rounding error 
         *
         * "sample_start = N" means "the first sample we need to represent is N
@@ -983,7 +1101,7 @@ WaveView::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) cons
         
        framepos_t sample_start = _region_start + (image_start * _samples_per_pixel);
        framepos_t sample_end   = _region_start + (image_end * _samples_per_pixel);
-
+       
        // cerr << "Sample space: " << sample_start << " .. " << sample_end << " @ " << _samples_per_pixel << " rs = " << _region_start << endl;
 
        /* sample_start and sample_end are bounded by the region
@@ -995,8 +1113,9 @@ WaveView::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) cons
        
        // cerr << debug_name() << " will need image spanning " << sample_start << " .. " << sample_end << " region spans " << _region_start << " .. " << region_end() << endl;
 
-       double image_offset;
-
+       double image_origin_in_self_coordinates;
+       boost::shared_ptr<WaveViewCache::Entry> image_to_draw;
+       
        if (_current_image) {
 
                /* check it covers the right sample range */
@@ -1007,29 +1126,40 @@ WaveView::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) cons
                } else {
                        /* timestamp our continuing use of this image/cache entry */
                        images->use (_region->audio_source (_channel), _current_image);
+                       image_to_draw = _current_image;
                }
        }
 
-       if (!_current_image) {
+       if (!image_to_draw) {
 
                /* look it up */
-               
-               _current_image = get_image (sample_start, sample_end);
 
-               if (!_current_image) {
+               bool full_image;
+               image_to_draw = get_image (sample_start, sample_end, full_image);
+
+               DEBUG_TRACE (DEBUG::WaveView, string_compose ("%1 image to draw = %2 (full? %3)\n", name, image_to_draw, full_image));
+               
+               if (!image_to_draw) {
                        /* image not currently available. A redraw will be scheduled
                           when it is ready.
                        */
                        return;
                }
+
+               if (full_image) {
+                       /* found an image that covers our entire sample range,
+                        * so keep a reference to it.
+                        */
+                       _current_image = image_to_draw;
+               }
        }
 
-       /* fix up offset: returned value is the first sample of the returned image */
+       /* compute the first pixel of the image that should be used when we
+        * render the specified range. 
+        */
 
-       image_offset = (_current_image->start - _region_start) / _samples_per_pixel;
+       image_origin_in_self_coordinates = (image_to_draw->start - _region_start) / _samples_per_pixel;
        
-       // cerr << "Offset into image to place at zero: " << image_offset << endl;
-
        if (_start_shift && (sample_start == _region_start) && (self.x0 == draw.x0)) {
                /* we are going to draw the first pixel for this region, but 
                   we may not want this to overlap a border around the
@@ -1037,25 +1167,65 @@ WaveView::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) cons
                */
                //cerr << name.substr (23) << " ss = " << sample_start << " rs = " << _region_start << " sf = " << _start_shift << " ds = " << draw_start << " self = " << self << " draw = " << draw << endl;
                //draw_start += _start_shift;
-               //image_offset += _start_shift;
+               //image_origin_in_self_coordinates += _start_shift;
        }
        
-       context->rectangle (draw_start, draw.y0, draw_end - draw_start, draw.height());
+       /* the image may only be a best-effort ... it may not span the entire
+        * range requested, though it is guaranteed to cover the start. So
+        * determine how many pixels we can actually draw.
+        */
+
+       double draw_width;
+       
+       if (image_to_draw != _current_image) {
+
+               /* the image is guaranteed to start at or before
+                * draw_start. But if it starts before draw_start, that reduces
+                * the maximum available width we can render with.
+                *
+                * so .. clamp the draw width to the smaller of what we need to
+                * draw or the available width of the image.
+                */
+
+               draw_width = min ((double) image_to_draw->image->get_width() - (draw_start - image_to_draw->start),
+                                 (draw_end - draw_start));
+
+
+               DEBUG_TRACE (DEBUG::WaveView, string_compose ("%1 draw just %2 of %3 (iwidth %4 off %5 img @ %6 rs @ %7)\n", name, draw_width, (draw_end - draw_start),
+                                                             image_to_draw->image->get_width(), image_origin_in_self_coordinates,
+                                                             image_to_draw->start, _region_start));
+       } else {
+               draw_width = draw_end - draw_start;
+               DEBUG_TRACE (DEBUG::WaveView, string_compose ("use current image, span entire render width %1..%2\n", draw_start, draw_end));
+       }
+
+       context->rectangle (draw_start, draw.y0, draw_width, draw.height());
 
        /* round image origin position to an exact pixel in device space to
         * avoid blurring
         */
 
-       double x  = self.x0 + image_offset;
+       double x  = self.x0 + image_origin_in_self_coordinates;
        double y  = self.y0;
        context->user_to_device (x, y);
        x = round (x);
        y = round (y);
        context->device_to_user (x, y);
 
-       context->set_source (_current_image->image, x, y);
+       /* the coordinates specify where in "user coordinates" (i.e. what we
+        * generally call "canvas coordinates" in this code) the image origin
+        * will appear. So specifying (10,10) will put the upper left corner of
+        * the image at (10,10) in user space.
+        */
+       
+       context->set_source (image_to_draw->image, x, y);
        context->fill ();
 
+       /* image obtained, some of it painted to display: we are rendered.
+          Future calls to get_image_in_thread are now meaningful.
+       */
+
+       rendered = true;
 }
 
 void
@@ -1116,6 +1286,7 @@ WaveView::gain_changed ()
        begin_visual_change ();
        invalidate_image_cache ();
        _region_amplitude = _region->scale_amplitude ();
+       get_image_in_thread = true;
        end_visual_change ();
 }
 
@@ -1170,6 +1341,7 @@ WaveView::set_amplitude_above_axis (double a)
                begin_visual_change ();
                invalidate_image_cache ();
                _amplitude_above_axis = a;
+               get_image_in_thread = true;
                end_visual_change ();
        }
 }
@@ -1266,7 +1438,6 @@ WaveView::set_start_shift (double pixels)
        _start_shift = pixels;
        end_visual_change ();
 }
-       
 
 void
 WaveView::cancel_my_render_request () const
@@ -1291,36 +1462,18 @@ WaveView::cancel_my_render_request () const
        
        request_queue.erase (this);
        current_request.reset ();
-}
+        DEBUG_TRACE (DEBUG::WaveView, string_compose ("%1 now has no request %2\n", this));
 
-void
-WaveView::send_request (boost::shared_ptr<WaveViewThreadRequest> req) const
-{      
-       if (req->type == WaveViewThreadRequest::Draw && current_request) {
-               /* this will stop rendering in progress (which might otherwise
-                  be long lived) for any current request.
-               */
-               current_request->cancel ();
-       }
-
-       start_drawing_thread ();
-
-       Glib::signal_idle().connect (sigc::bind (sigc::mem_fun (*this, &WaveView::idle_send_request), req));
 }
 
-bool
-WaveView::idle_send_request (boost::shared_ptr<WaveViewThreadRequest> req) const
+void
+WaveView::set_image_cache_size (uint64_t sz)
 {
-       {
-               Glib::Threads::Mutex::Lock lm (request_queue_lock);
-               /* swap requests (protected by lock) */
-               current_request = req;
-               request_queue.insert (this);
+       if (!images) {
+               images = new WaveViewCache;
        }
 
-       request_cond.signal (); /* wake thread */
-       
-       return false; /* do not call from idle again */
+       images->set_image_cache_threshold (sz);
 }
 
 /*-------------------------------------------------*/
@@ -1371,6 +1524,8 @@ WaveView::drawing_thread ()
                requestor = *(request_queue.begin());
                request_queue.erase (request_queue.begin());
 
+                DEBUG_TRACE (DEBUG::WaveView, string_compose ("start request for %1 at %2\n", requestor, g_get_monotonic_time()));
+
                boost::shared_ptr<WaveViewThreadRequest> req = requestor->current_request;
 
                if (!req) {
@@ -1419,7 +1574,8 @@ WaveViewCache::lookup_image (boost::shared_ptr<ARDOUR::AudioSource> src,
                              Coord height,
                              float amplitude,
                              Color fill_color,
-                             double samples_per_pixel)
+                             double samples_per_pixel,
+                             bool& full_coverage)
 {
        ImageCache::iterator x;
        
@@ -1429,7 +1585,9 @@ WaveViewCache::lookup_image (boost::shared_ptr<ARDOUR::AudioSource> src,
        }
 
        CacheLine& caches = x->second;
-
+       boost::shared_ptr<Entry> best_partial;
+       framecnt_t max_coverage = 0;
+       
        /* Find a suitable ImageSurface, if it exists.
        */
 
@@ -1445,13 +1603,36 @@ WaveViewCache::lookup_image (boost::shared_ptr<ARDOUR::AudioSource> src,
                        continue;
                }
 
-               if (end <= e->end && start >= e->start) {
-                       /* found an image that covers the range we need */
+                switch (Evoral::coverage (start, end, e->start, e->end)) {
+                case Evoral::OverlapExternal:  /* required range is inside image range */
+                       DEBUG_TRACE (DEBUG::WaveView, string_compose ("found image spanning %1..%2 covers %3..%4\n",
+                                                                     e->start, e->end, start, end));
                        use (src, e);
-                       return e;
+                        full_coverage = true;
+                        return e;
+
+                case Evoral::OverlapStart: /* required range start is covered by image range */
+                        if ((e->end - start) > max_coverage) {
+                                best_partial = e;
+                                max_coverage = e->end - start;
+                        }
+                        break;
+
+                case Evoral::OverlapNone:
+                case Evoral::OverlapEnd:
+                case Evoral::OverlapInternal:
+                        break;
                }
        }
 
+       if (best_partial) {
+               DEBUG_TRACE (DEBUG::WaveView, string_compose ("found PARTIAL image spanning %1..%2 partially covers %3..%4\n",
+                                                             best_partial->start, best_partial->end, start, end));
+               use (src, best_partial);
+               full_coverage = false;
+               return best_partial;
+       }
+
        return boost::shared_ptr<Entry> ();
 }
 
@@ -1525,8 +1706,11 @@ WaveViewCache::consolidate_image_cache (boost::shared_ptr<ARDOUR::AudioSource> s
                        
                        if (e2->start >= e1->start && e2->end <= e1->end) {
                                /* c2 is fully contained by c1, so delete it */
-                               c2 = caches.erase (c2);
-                               continue;
+                               caches.erase (c2);
+
+                               /* and re-start the whole iteration */
+                               nxt = caches.begin ();
+                               break;
                        }
 
                        c2 = nxt2;
@@ -1558,7 +1742,6 @@ WaveViewCache::add (boost::shared_ptr<ARDOUR::AudioSource> src, boost::shared_pt
        ce->timestamp = g_get_monotonic_time ();
 
        cache_map[src].push_back (ce);
-       cache_list.push_back (make_pair (src, ce));
 }
 
 uint64_t
@@ -1584,51 +1767,62 @@ WaveViewCache::cache_full()
 void
 WaveViewCache::cache_flush ()
 {
-       SortByTimestamp sorter;
+       /* Build a sortable list of all cache entries */
+       
+       CacheList cache_list;
 
+       for (ImageCache::const_iterator cm = cache_map.begin(); cm != cache_map.end(); ++cm) {
+               for (CacheLine::const_iterator cl = cm->second.begin(); cl != cm->second.end(); ++cl) {
+                       cache_list.push_back (make_pair (cm->first, *cl));
+               }
+       }
+       
        /* sort list in LRU order */
-
+       SortByTimestamp sorter;
        sort (cache_list.begin(), cache_list.end(), sorter);
 
-       while (image_cache_size > _image_cache_threshold) {
+       while (image_cache_size > _image_cache_threshold && !cache_map.empty() && !cache_list.empty()) {
 
                ListEntry& le (cache_list.front());
 
                ImageCache::iterator x;
                
-               if ((x = cache_map.find (le.first)) == cache_map.end ()) {
-                       /* wierd ... no entry for this AudioSource */
-                       continue;
-               }
+               if ((x = cache_map.find (le.first)) != cache_map.end ()) {
                
-               CacheLine& cl  = x->second;
-
-               for (CacheLine::iterator c = cl.begin(); c != cl.end(); ++c) {
-
-                       if (*c == le.second) {
-
-                               /* Remove this entry from this cache line */
-                               cl.erase (c);
-
-                               if (cl.empty()) {
-                                       /* remove cache line from main cache: no more entries */
-                                       cache_map.erase (x);
+                       CacheLine& cl  = x->second;
+                       
+                       for (CacheLine::iterator c = cl.begin(); c != cl.end(); ++c) {
+                               
+                               if (*c == le.second) {
+
+                                       DEBUG_TRACE (DEBUG::WaveView, string_compose ("Removing cache line entry for %1\n", x->first->name()));
+                                       
+                                       /* Remove this entry from this cache line */
+                                       cl.erase (c);
+                                       
+                                       if (cl.empty()) {
+                                               /* remove cache line from main cache: no more entries */
+                                               cache_map.erase (x);
+                                       }
+                                       
+                                       break;
                                }
-
-                               break;
                        }
-               }
-               
-               Cairo::RefPtr<Cairo::ImageSurface> img (le.second->image);
-               uint64_t size = img->get_height() * img->get_width() * 4; /* 4 = bytes per FORMAT_ARGB32 pixel */
-
-               if (image_cache_size > size) {
-                       image_cache_size -= size;
-               } else {
-                       image_cache_size = 0;
+                       
+                       Cairo::RefPtr<Cairo::ImageSurface> img (le.second->image);
+                       uint64_t size = img->get_height() * img->get_width() * 4; /* 4 = bytes per FORMAT_ARGB32 pixel */
+                       
+                       if (image_cache_size > size) {
+                               image_cache_size -= size;
+                       } else {
+                               image_cache_size = 0;
+                       }
+                       DEBUG_TRACE (DEBUG::WaveView, string_compose ("cache shrunk to %1\n", image_cache_size));
                }
       
-               /* Remove from the linear list */
+               /* Remove from the linear list, even if we didn't find it in
+                * the actual cache_mao
+                */
                cache_list.erase (cache_list.begin());
        }
 }
@@ -1636,6 +1830,7 @@ WaveViewCache::cache_flush ()
 void
 WaveViewCache::set_image_cache_threshold (uint64_t sz)
 {
+       DEBUG_TRACE (DEBUG::WaveView, string_compose ("new image cache size \n", sz));
        _image_cache_threshold = sz;
        cache_flush ();
 }