Fix 0006183 (waveview crash).
[ardour.git] / libs / canvas / wave_view.cc
index 7db6522d54209c1abfb2dcbe50da5a080e543199..3521ef33cd20bc610a745ceb7196cf06c7baab64 100644 (file)
@@ -34,6 +34,7 @@
 #include "canvas/wave_view.h"
 #include "canvas/utils.h"
 #include "canvas/canvas.h"
+#include "canvas/colors.h"
 
 #include <gdkmm/general.h>
 
@@ -70,6 +71,7 @@ WaveView::WaveView (Canvas* c, 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())
 {
        VisualPropertiesChanged.connect_same_thread (invalidation_connection, boost::bind (&WaveView::handle_visual_property_change, this));
@@ -123,7 +125,7 @@ WaveView::handle_visual_property_change ()
                _gradient_depth = global_gradient_depth();
                changed = true;
        }
-       
+
        if (changed) {
                begin_visual_change ();
                invalidate_image_cache ();
@@ -170,17 +172,11 @@ WaveView::set_samples_per_pixel (double samples_per_pixel)
                invalidate_image_cache ();
                _samples_per_pixel = samples_per_pixel;
                _bounding_box_dirty = true;
-               
+
                end_change ();
        }
 }
 
-static inline double
-image_to_window (double wave_origin, double image_start)
-{
-       return wave_origin + image_start;
-}
-
 static inline double
 window_to_image (double wave_origin, double image_start)
 {
@@ -215,6 +211,21 @@ WaveView::invalidate_image_cache ()
        vector <uint32_t> deletion_list;
        vector <CacheEntry> caches;
 
+       /* The source may have disappeared in the case of rec regions.*/
+       if (_region->n_channels() == 0) {
+               std::map <boost::shared_ptr<ARDOUR::AudioSource>, std::vector <CacheEntry> >::iterator i;
+               for (i = _image_cache.begin(); i != _image_cache.end(); ++i) {
+                       if (i->first.unique()) {
+                               for (uint32_t n = 0; n < (*i).second.size (); ++n) {
+                                       (*i).second[n].image.clear ();
+                               }
+                               (*i).second.clear ();
+                               _image_cache.erase(i->first);
+                       }
+               }
+               return;
+       }
+
        if (_image_cache.find (_region->audio_source ()) != _image_cache.end ()) {
                caches = _image_cache.find (_region->audio_source ())->second;
        } else {
@@ -223,17 +234,15 @@ WaveView::invalidate_image_cache ()
 
        for (uint32_t i = 0; i < caches.size (); ++i) {
 
-               if (_channel != caches[i].channel 
+               if (_channel != caches[i].channel
                    || _height != caches[i].height
-                   || _region_amplitude != caches[i].amplitude 
-                   || _fill_color != caches[i].fill_color 
-                   || _outline_color != caches[i].outline_color) {
+                   || _region_amplitude != caches[i].amplitude
+                   || _fill_color != caches[i].fill_color) {
 
                        continue;
                }
 
                deletion_list.push_back (i);
-               
        }
 
        while (deletion_list.size() > 0) {
@@ -247,7 +256,6 @@ WaveView::invalidate_image_cache ()
        } else {
                _image_cache[_region->audio_source ()] = caches;
        }
-
 }
 
 void
@@ -263,11 +271,10 @@ WaveView::consolidate_image_cache () const
 
        for (uint32_t i = 0; i < caches.size (); ++i) {
 
-               if (_channel != caches[i].channel 
+               if (_channel != caches[i].channel
                    || _height != caches[i].height
-                   || _region_amplitude != caches[i].amplitude 
-                   || _fill_color != caches[i].fill_color 
-                   || _outline_color != caches[i].outline_color) {
+                   || _region_amplitude != caches[i].amplitude
+                   || _fill_color != caches[i].fill_color) {
 
                        other_entries++;
                        continue;
@@ -278,11 +285,10 @@ WaveView::consolidate_image_cache () const
 
                for (uint32_t j = i; j < caches.size (); ++j) {
 
-                       if (i == j || _channel != caches[j].channel 
-                           || _height != caches[i].height 
-                           || _region_amplitude != caches[i].amplitude 
-                           || _fill_color != caches[i].fill_color 
-                           || _outline_color != caches[i].outline_color) {
+                       if (i == j || _channel != caches[j].channel
+                           || _height != caches[i].height
+                           || _region_amplitude != caches[i].amplitude
+                           || _fill_color != caches[i].fill_color) {
 
                                continue;
                        }
@@ -303,7 +309,7 @@ WaveView::consolidate_image_cache () const
                deletion_list.pop_back();
        }
 
-       /* We don't care if this channel/height/amplitude has anything in the cache - just drop the Last Added entries 
+       /* We don't care if this channel/height/amplitude has anything in the cache - just drop the Last Added entries
           until we reach a size where there is a maximum of CACHE_HIGH_WATER + other entries.
        */
 
@@ -319,19 +325,115 @@ WaveView::consolidate_image_cache () const
        }
 }
 
+Coord
+WaveView::y_extent (double s, bool /*round_to_lower_edge*/) 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...
+                */
+               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)));
+       }
+}
+
+void
+WaveView::draw_absent_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peaks, int n_peaks) const
+{
+       Cairo::RefPtr<Cairo::ImageSurface> stripe = Cairo::ImageSurface::create (Cairo::FORMAT_A8, n_peaks, _height);
+
+       Cairo::RefPtr<Cairo::Context> stripe_context = Cairo::Context::create (stripe);
+       stripe_context->set_antialias (Cairo::ANTIALIAS_NONE);
+
+       uint32_t stripe_separation = 150;
+       double start = - floor (_height / stripe_separation) * stripe_separation;
+       int stripe_x = 0;
+
+       while (start < n_peaks) {
+
+               stripe_context->move_to (start, 0);
+               stripe_x = start + _height;
+               stripe_context->line_to (stripe_x, _height);
+               start += stripe_separation;
+       }
+
+       stripe_context->set_source_rgba (1.0, 1.0, 1.0, 1.0);
+       stripe_context->set_line_cap (Cairo::LINE_CAP_SQUARE);
+       stripe_context->set_line_width(50);
+       stripe_context->stroke();
+
+       Cairo::RefPtr<Cairo::Context> context = Cairo::Context::create (image);
+
+       context->set_source_rgba (1.0, 1.0, 0.0, 0.3);
+       context->mask (stripe, 0, 0);
+       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;
+       Cairo::RefPtr<Cairo::ImageSurface> clip;
+       Cairo::RefPtr<Cairo::ImageSurface> zero;
+
+       ImageSet() :
+               wave (0), outline (0), clip (0), zero (0) {}
+};
+
 void
 WaveView::draw_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peaks, int n_peaks) const
 {
-       Cairo::RefPtr<Cairo::Context> context = Cairo::Context::create (image);
+
+       ImageSet images;
+
+       images.wave = Cairo::ImageSurface::create (Cairo::FORMAT_A8, n_peaks, _height);
+       images.outline = Cairo::ImageSurface::create (Cairo::FORMAT_A8, n_peaks, _height);
+       images.clip = Cairo::ImageSurface::create (Cairo::FORMAT_A8, n_peaks, _height);
+       images.zero = Cairo::ImageSurface::create (Cairo::FORMAT_A8, n_peaks, _height);
+
+       Cairo::RefPtr<Cairo::Context> wave_context = Cairo::Context::create (images.wave);
+       Cairo::RefPtr<Cairo::Context> outline_context = Cairo::Context::create (images.outline);
+       Cairo::RefPtr<Cairo::Context> clip_context = Cairo::Context::create (images.clip);
+       Cairo::RefPtr<Cairo::Context> zero_context = Cairo::Context::create (images.zero);
+       wave_context->set_antialias (Cairo::ANTIALIAS_NONE);
+       outline_context->set_antialias (Cairo::ANTIALIAS_NONE);
+       clip_context->set_antialias (Cairo::ANTIALIAS_NONE);
+       zero_context->set_antialias (Cairo::ANTIALIAS_NONE);
+
        boost::scoped_array<LineTips> tips (new LineTips[n_peaks]);
 
        /* Clip level nominally set to -0.9dBFS to account for inter-sample
@@ -355,97 +457,262 @@ WaveView::draw_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peak
 
                if (_logscaled) {
                        for (int i = 0; i < n_peaks; ++i) {
-                               tips[i].bot = height();
-                               tips[i].top = y_extent (alt_log_meter (fast_coefficient_to_dB (max (fabs (_peaks[i].max), fabs (_peaks[i].min)))));
 
-                               if (fabs (_peaks[i].max) >= clip_level) {
+                               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);
+
+                               if (_peaks[i].max >= clip_level) {
                                        tips[i].clip_max = true;
                                }
 
-                               if (fabs (_peaks[i].min) >= clip_level) {
+                               if (-(_peaks[i].min) >= clip_level) {
                                        tips[i].clip_min = true;
                                }
                        }
-               } else {for (int i = 0; i < n_peaks; ++i) {
-                               tips[i].bot = height();
-                               tips[i].top = y_extent (max (fabs (_peaks[i].max), fabs (_peaks[i].min)));
 
-                               if (fabs (_peaks[i].max) >= clip_level) {
-                                       tips[i].clip_max = true;
-                               }
+               } else {
+                       for (int i = 0; i < n_peaks; ++i) {
 
-                               if (fabs (_peaks[i].min) >= clip_level) {
-                                       tips[i].clip_min = true;
+                               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);
+                               if (p >= clip_level) {
+                                       tips[i].clip_max = true;
                                }
                        }
+
                }
 
        } else {
 
                if (_logscaled) {
                        for (int i = 0; i < n_peaks; ++i) {
-                               Coord top = _peaks[i].min;
-                               Coord bot = _peaks[i].max;
+                               double top = _peaks[i].max;
+                               double bot = _peaks[i].min;
 
-                               if (fabs (top) >= clip_level) {
-                                       tips[i].clip_max = true;
+                               if (_peaks[i].max >= clip_level) {
+                                               tips[i].clip_max = true;
                                }
-
-                               if (fabs (bot) >= clip_level) {
+                               if (-(_peaks[i].min) >= clip_level) {
                                        tips[i].clip_min = true;
                                }
 
                                if (top > 0.0) {
-                                       top = y_extent (alt_log_meter (fast_coefficient_to_dB (top)));
+                                       top = alt_log_meter (fast_coefficient_to_dB (top));
                                } else if (top < 0.0) {
-                                       top = y_extent (-alt_log_meter (fast_coefficient_to_dB (-top)));
+                                       top =-alt_log_meter (fast_coefficient_to_dB (-top));
                                } else {
-                                       top = y_extent (0.0);
+                                       top = 0.0;
                                }
 
                                if (bot > 0.0) {
-                                       bot = y_extent (alt_log_meter (fast_coefficient_to_dB (bot)));
+                                       bot = alt_log_meter (fast_coefficient_to_dB (bot));
                                } else if (bot < 0.0) {
-                                       bot = y_extent (-alt_log_meter (fast_coefficient_to_dB (-bot)));
+                                       bot = -alt_log_meter (fast_coefficient_to_dB (-bot));
                                } else {
-                                       bot = y_extent (0.0);
+                                       bot = 0.0;
                                }
 
-                               tips[i].top = top;
-                               tips[i].bot = bot;
-                       } 
+                               tips[i].top = y_extent (top, false);
+                               tips[i].bot = y_extent (bot, true);
+                               tips[i].spread = tips[i].bot - tips[i].top;
+                       }
 
                } else {
                        for (int i = 0; i < n_peaks; ++i) {
-
-                               if (fabs (_peaks[i].max) >= clip_level) {
+                               if (_peaks[i].max >= clip_level) {
                                        tips[i].clip_max = true;
                                }
-
-                               if (fabs (_peaks[i].min) >= clip_level) {
+                               if (-(_peaks[i].min) >= clip_level) {
                                        tips[i].clip_min = true;
                                }
 
-                               tips[i].top = y_extent (_peaks[i].min);
-                               tips[i].bot = y_extent (_peaks[i].max);
+                               tips[i].top = y_extent (_peaks[i].max, false);
+                               tips[i].bot = y_extent (_peaks[i].min, true);
+                               tips[i].spread = tips[i].bot - tips[i].top;
+                       }
+
+               }
+       }
+       Color alpha_one = rgba_to_color (0, 0, 0, 1.0);
+
+       set_source_rgba (wave_context, alpha_one);
+       set_source_rgba (outline_context, alpha_one);
+       set_source_rgba (clip_context, alpha_one);
+       set_source_rgba (zero_context, alpha_one);
+
+       /* ensure single-pixel lines */
+
+       wave_context->set_line_width (1.0);
+       wave_context->translate (0.5, +0.5);
+
+       outline_context->set_line_width (1.0);
+       outline_context->translate (0.5, +0.5);
+
+       clip_context->set_line_width (1.0);
+       clip_context->translate (0.5, +0.5);
+
+       zero_context->set_line_width (1.0);
+       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.
+        */
+
+       const double clip_height = min (7.0, ceil (_height * 0.05));
+       bool draw_outline_as_wave = false;
+
+       /* There are 3 possible components to draw at each x-axis position: the
+          waveform "line", the zero line and an outline/clip indicator.  We
+          have to decide which of the 3 to draw at each position, pixel by
+          pixel. This makes the rendering less efficient but it is the only
+          way I can see to do this correctly.
+
+          To avoid constant source swapping and stroking, we draw the components separately
+          onto four alpha only image surfaces for use as a mask.
 
+          With only 1 pixel of spread between the top and bottom of the line,
+          we just draw the upper outline/clip indicator.
 
+          With 2 pixels of spread, we draw the upper and lower outline clip
+          indicators.
+
+          With 3 pixels of spread we draw the upper and lower outline/clip
+          indicators and at least 1 pixel of the waveform line.
+
+          With 5 pixels of spread, we draw all components.
+
+          We can do rectified as two separate passes because we have a much
+          easier decision regarding whether to draw the waveform line. We
+          always draw the clip/outline indicators.
+       */
+
+       if (_shape == WaveView::Rectified) {
+
+               for (int i = 0; i < n_peaks; ++i) {
+
+                       /* waveform line */
+
+                       if (tips[i].spread >= 1.0) {
+                               wave_context->move_to (i, tips[i].top);
+                               wave_context->line_to (i, tips[i].bot);
+                       }
+
+                       if (_global_show_waveform_clipping && (tips[i].clip_max)) {
+                               clip_context->move_to (i, tips[i].top);
+                               /* clip-indicating upper terminal line */
+                               clip_context->rel_line_to (0, min (clip_height, ceil(tips[i].spread + .5)));
+                       } else {
+                               outline_context->move_to (i, tips[i].top);
+                               /* normal upper terminal dot */
+                               outline_context->close_path ();
                        }
                }
+
+               wave_context->stroke ();
+               clip_context->stroke ();
+               outline_context->stroke ();
+
+       } else {
+               const double height_2 = (_height - 4.0) * .5;
+
+               for (int i = 0; i < n_peaks; ++i) {
+
+                       /* waveform line */
+
+                       if (tips[i].spread >= 2.0) {
+                               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) {
+                                       wave_context->move_to (i-1, tips[i-1].top);
+                                       wave_context->line_to (i-1, (tips[i].bot + tips[i-1].top)/2);
+                                       wave_context->move_to (i, (tips[i].bot + tips[i-1].top)/2);
+                                       wave_context->line_to (i, tips[i].top);
+                               } else if (tips[i-1].bot > tips[i].bot + 2) {
+                                       wave_context->move_to (i-1, tips[i-1].bot);
+                                       wave_context->line_to (i-1, (tips[i].top + tips[i-1].bot)/2);
+                                       wave_context->move_to (i, (tips[i].top + tips[i-1].bot)/2);
+                                       wave_context->line_to (i, tips[i].bot);
+                               }
+                       }
+
+                       /* zero line */
+
+                       if (tips[i].spread >= 5.0 && show_zero_line()) {
+                               zero_context->move_to (i, floor(height_2));
+                               zero_context->rel_line_to (1.0, 0);
+                       }
+
+                       if (tips[i].spread > 1.0) {
+                               draw_outline_as_wave = false;
+                               /* lower outline/clip indicator */
+                               if (_global_show_waveform_clipping && tips[i].clip_min) {
+                                       clip_context->move_to (i, tips[i].bot);
+                                       /* clip-indicating lower terminal line */
+                                       const double sign = tips[i].bot > height_2 ? -1 : 1;
+                                       clip_context->rel_line_to (0, sign * min (clip_height, ceil (tips[i].spread + .5)));
+                               } else {
+                                       outline_context->move_to (i, tips[i].bot + 0.5);
+                                       /* normal lower terminal dot */
+                                       outline_context->rel_line_to (0, -0.5);
+                               }
+                       } else {
+                               draw_outline_as_wave = true;
+                               if (tips[i].clip_min) {
+                                       // make sure we draw the clip
+                                       tips[i].clip_max = true;
+                               }
+                       }
+
+                       /* upper outline/clip indicator */
+                       if (_global_show_waveform_clipping && tips[i].clip_max) {
+                               clip_context->move_to (i, tips[i].top);
+                               /* clip-indicating upper terminal line */
+                               const double sign = tips[i].top > height_2 ? -1 : 1;
+                               clip_context->rel_line_to (0, sign * min(clip_height, ceil(tips[i].spread + .5)));
+                       } else {
+                               if (draw_outline_as_wave) {
+                                       wave_context->move_to (i, tips[i].top + 0.5);
+                                       /* special case where outline only is drawn.
+                                          is this correct? too short by 0.5?
+                                       */
+                                       wave_context->rel_line_to (0, -0.5);
+                               } else {
+                                       outline_context->move_to (i, tips[i].top + 0.5);
+                                       /* normal upper terminal dot */
+                                       outline_context->rel_line_to (0, -0.5);
+                               }
+                       }
+               }
+
+               wave_context->stroke ();
+               outline_context->stroke ();
+               clip_context->stroke ();
+               zero_context->stroke ();
        }
 
+       Cairo::RefPtr<Cairo::Context> context = Cairo::Context::create (image);
+
+       /* Here we set a source colour and use the various components as a mask. */
+
        if (gradient_depth() != 0.0) {
-                       
+
                Cairo::RefPtr<Cairo::LinearGradient> gradient (Cairo::LinearGradient::create (0, 0, 0, _height));
-                       
+
                double stops[3];
-                       
+
                double r, g, b, a;
 
                if (_shape == Rectified) {
                        stops[0] = 0.1;
-                       stops[0] = 0.3;
-                       stops[0] = 0.9;
+                       stops[1] = 0.3;
+                       stops[2] = 0.9;
                } else {
                        stops[0] = 0.1;
                        stops[1] = 0.5;
@@ -453,95 +720,37 @@ WaveView::draw_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peak
                }
 
                color_to_rgba (_fill_color, r, g, b, a);
-               gradient->add_color_stop_rgba (stops[0], r, g, b, a);
-               gradient->add_color_stop_rgba (stops[2], r, g, b, a);
-
+               gradient->add_color_stop_rgba (stops[1], r, g, b, a);
                /* generate a new color for the middle of the gradient */
                double h, s, v;
                color_to_hsv (_fill_color, h, s, v);
                /* change v towards white */
                v *= 1.0 - gradient_depth();
-               Color center = hsv_to_color (h, s, v, a);
+               Color center = hsva_to_color (h, s, v, a);
                color_to_rgba (center, r, g, b, a);
-               gradient->add_color_stop_rgba (stops[1], r, g, b, a);
-                       
-               context->set_source (gradient);
-       } else {
-               set_source_rgba (context, _fill_color);
-       }
 
-       /* ensure single-pixel lines */
-               
-       context->set_line_width (0.5);
-       context->translate (0.5, 0.0);
-
-       /* draw the lines */
+               gradient->add_color_stop_rgba (stops[0], r, g, b, a);
+               gradient->add_color_stop_rgba (stops[2], r, g, b, a);
 
-       if (_shape == WaveView::Rectified) {
-               for (int i = 0; i < n_peaks; ++i) {
-                       context->move_to (i, tips[i].top); /* down 1 pixel */
-                       context->line_to (i, tips[i].bot);
-               }
+               context->set_source (gradient);
        } else {
-               for (int i = 0; i < n_peaks; ++i) {
-                       context->move_to (i, tips[i].top);
-                       context->line_to (i, tips[i].bot);
-               }
-       }
-
-       context->stroke ();
-
-       /* zero line goes next, so that the outline/clip is on top of it 
-        */
-       
-       if (show_zero_line()) {
-               set_source_rgba (context, _zero_color);
-               context->set_line_width (1.0);
-               context->move_to (0, y_extent (0.0) + 0.5);
-               context->line_to (n_peaks, y_extent (0.0) + 0.5);
-               context->stroke ();
+               set_source_rgba (context, _fill_color);
        }
 
-       /* now add dots to the top and bottom of each line (this is
-        * modelled on pyramix, except that we also visual indicate 
-        * clipping if it occurs).
-        *
-        * the height of the clip-indicator should be at most 7 pixels,
-        * or 5% of the height of the waveview item.
-        */
-
-       const double clip_height = min (7.0, ceil (_height * 0.05));
+       context->mask (images.wave, 0, 0);
+       context->fill ();
 
        set_source_rgba (context, _outline_color);
+       context->mask (images.outline, 0, 0);
+       context->fill ();
 
-       for (int i = 0; i < n_peaks; ++i) {
-
-               context->move_to (i, tips[i].top);
-               if (_global_show_waveform_clipping && ((_shape == WaveView::Rectified && (tips[i].clip_max || tips[i].clip_min)) || tips[i].clip_max)) {
-                       /* clip-indicating upper terminal line */
-                       set_source_rgba (context, _clip_color);
-                       context->rel_line_to (0, clip_height);
-                       context->stroke ();
-                       set_source_rgba (context, _outline_color);
-               } else {
-                       /* normal upper terminal dot */
-                       context->rel_line_to (0, 1.0);
-                       context->stroke ();
-               }
+       set_source_rgba (context, _clip_color);
+       context->mask (images.clip, 0, 0);
+       context->fill ();
 
-               context->move_to (i, tips[i].bot);
-               if (_global_show_waveform_clipping && _shape != WaveView::Rectified && tips[i].clip_min) {
-                       /* clip-indicating lower terminal line */
-                       set_source_rgba (context, _clip_color);
-                       context->rel_line_to (0, -clip_height);
-                       context->stroke ();
-                       set_source_rgba (context, _outline_color);
-               } else {
-                       /* normal lower terminal dot */
-                       context->rel_line_to (0, -1.0);
-                       context->stroke ();
-               }
-       }
+       set_source_rgba (context, _zero_color);
+       context->mask (images.zero, 0, 0);
+       context->fill ();
 
 }
 
@@ -551,7 +760,7 @@ WaveView::get_image (Cairo::RefPtr<Cairo::ImageSurface>& image, framepos_t start
        vector <CacheEntry> caches;
 
        if (_image_cache.find (_region->audio_source ()) != _image_cache.end ()) {
-               
+
                caches = _image_cache.find (_region->audio_source ())->second;
        }
 
@@ -559,11 +768,10 @@ WaveView::get_image (Cairo::RefPtr<Cairo::ImageSurface>& image, framepos_t start
        */
        for (uint32_t i = 0; i < caches.size (); ++i) {
 
-               if (_channel != caches[i].channel 
+               if (_channel != caches[i].channel
                    || _height != caches[i].height
-                   || _region_amplitude != caches[i].amplitude 
-                   || _fill_color != caches[i].fill_color 
-                   || _outline_color != caches[i].outline_color) {
+                   || _region_amplitude != caches[i].amplitude
+                   || _fill_color != caches[i].fill_color) {
 
                        continue;
                }
@@ -572,7 +780,7 @@ WaveView::get_image (Cairo::RefPtr<Cairo::ImageSurface>& image, framepos_t start
                framepos_t segment_end = caches[i].end;
 
                if (end <= segment_end && start >= segment_start) {
-                       image_offset = (segment_start - _region->start()) / _samples_per_pixel;
+                       image_offset = (segment_start - _region_start) / _samples_per_pixel;
                        image = caches[i].image;
 
                        return;
@@ -582,9 +790,9 @@ WaveView::get_image (Cairo::RefPtr<Cairo::ImageSurface>& image, framepos_t start
        consolidate_image_cache ();
 
        /* sample position is canonical here, and we want to generate
-        * an image that spans about twice the canvas width 
+        * an image that spans about twice the canvas width
         */
-       
+
        const framepos_t center = start + ((end - start) / 2);
        const framecnt_t canvas_samples = _canvas->visible_area().width() * _samples_per_pixel; /* one canvas width */
 
@@ -598,16 +806,21 @@ WaveView::get_image (Cairo::RefPtr<Cairo::ImageSurface>& image, framepos_t start
 
        boost::scoped_array<ARDOUR::PeakData> peaks (new PeakData[n_peaks]);
 
-       _region->read_peaks (peaks.get(), n_peaks, 
+       framecnt_t peaks_read;
+       peaks_read = _region->read_peaks (peaks.get(), n_peaks,
                             sample_start, sample_end - sample_start,
-                            _channel, 
+                            _channel,
                             _samples_per_pixel);
 
-       image = Cairo::ImageSurface::create (Cairo::FORMAT_ARGB32, ((double)(sample_end - sample_start)) / _samples_per_pixel, _height);
+       image = Cairo::ImageSurface::create (Cairo::FORMAT_ARGB32, n_peaks, _height);
 
-       draw_image (image, peaks.get(), n_peaks);
+       if (peaks_read > 0) {
+               draw_image (image, peaks.get(), n_peaks);
+       } else {
+               draw_absent_image (image, peaks.get(), n_peaks);
+       }
 
-       _image_cache[_region->audio_source ()].push_back (CacheEntry (_channel, _height, _region_amplitude, _fill_color, _outline_color, sample_start,  sample_end, image));
+       _image_cache[_region->audio_source ()].push_back (CacheEntry (_channel, _height, _region_amplitude, _fill_color, sample_start,  sample_end, image));
 
        image_offset = (sample_start - _region->start()) / _samples_per_pixel;
 
@@ -625,29 +838,29 @@ WaveView::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) cons
                return;
        }
 
-       Rect self = item_to_window (Rect (0.5, 0.0, _region->length() / _samples_per_pixel, _height));
+       Rect self = item_to_window (Rect (0.0, 0.0, _region->length() / _samples_per_pixel, _height));
        boost::optional<Rect> d = self.intersection (area);
 
        if (!d) {
                return;
        }
-       
+
        Rect draw = d.get();
 
        /* window coordinates - pixels where x=0 is the left edge of the canvas
         * window. We round down in case we were asked to
         * draw "between" pixels at the start and/or end.
         */
-
-       const double draw_start = floor (draw.x0);
+       
+       double draw_start = floor (draw.x0);
        const double draw_end = floor (draw.x1);
 
        // cerr << "Need to draw " << draw_start << " .. " << draw_end << endl;
-       
+
        /* image coordnates: pixels where x=0 is the start of this waveview,
         * wherever it may be positioned. thus image_start=N means "an image
         * that beings N pixels after the start of region that this waveview is
-        * representing. 
+        * representing.
         */
 
        const framepos_t image_start = window_to_image (self.x0, draw_start);
@@ -658,7 +871,7 @@ WaveView::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) cons
        /* sample coordinates - note, these are not subject to rounding error */
        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 << endl;
 
        Cairo::RefPtr<Cairo::ImageSurface> image;
@@ -668,6 +881,16 @@ WaveView::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) cons
 
        // 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
+                  waveform. If so, _start_shift will be set.
+               */
+               //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;
+       }
+       
        context->rectangle (draw_start, draw.y0, draw_end - draw_start, draw.height());
 
        /* round image origin position to an exact pixel in device space to
@@ -683,6 +906,7 @@ WaveView::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) cons
 
        context->set_source (image, x, y);
        context->fill ();
+
 }
 
 void
@@ -693,10 +917,10 @@ WaveView::compute_bounding_box () const
        } else {
                _bounding_box = boost::optional<Rect> ();
        }
-       
+
        _bounding_box_dirty = false;
 }
-       
+
 void
 WaveView::set_height (Distance height)
 {
@@ -819,45 +1043,36 @@ WaveView::set_global_logscaled (bool yn)
 }
 
 void
-WaveView::region_resized ()
+WaveView::set_region_start (frameoffset_t start)
 {
        if (!_region) {
                return;
        }
 
-       /* special: do not use _region->length() here to compute
-          bounding box because it will already have changed.
-          
-          if we have a bounding box, use it.
-       */
-
-       _pre_change_bounding_box = _bounding_box;
+       if (_region_start == start) {
+               return;
+       }
 
+       begin_change ();
+       _region_start = start;
        _bounding_box_dirty = true;
-       compute_bounding_box ();
-
        end_change ();
 }
 
-Coord
-WaveView::y_extent (double s) const
+void
+WaveView::region_resized ()
 {
-       /* it is important that this returns an integral value, so that we 
-          can ensure correct single pixel behaviour.
-        */
-
-       Coord pos;
+       /* Called when the region start or end (thus length) has changed.
+       */
 
-       switch (_shape) {
-       case Rectified:
-               pos = floor (_height - (s * _height));
-               break;
-       default:
-               pos = floor ((1.0-s) * (_height / 2.0));
-               break;
+       if (!_region) {
+               return;
        }
 
-       return min (_height, (max (0.0, pos)));
+       begin_change ();
+       _region_start = _region->start();
+       _bounding_box_dirty = true;
+       end_change ();
 }
 
 void
@@ -874,7 +1089,19 @@ WaveView::set_global_show_waveform_clipping (bool yn)
 {
        if (_global_show_waveform_clipping != yn) {
                _global_show_waveform_clipping = yn;
-               VisualPropertiesChanged (); /* EMIT SIGNAL */
+               ClipLevelChanged ();
        }
 }
 
+void
+WaveView::set_start_shift (double pixels)
+{
+       if (pixels < 0) {
+               return;
+       }
+
+       begin_visual_change ();
+       _start_shift = pixels;
+       end_visual_change ();
+}
+