[pitivi: 15/18] previewer.py: cache and display waveforms at multiple resolutions

[Edward Hervey <edwardrv src gnome org>]

commit bb23f7cd1a2d84b44788dc937bc46b009b3d26ef
Author: Brandon Lewis <brandon_lewis alum berkeley edu>
Date:   Tue Nov 3 00:05:30 2009 -0800

    previewer.py: cache and display waveforms at multiple resolutions
    
    The waveform previewer was exceeding some kind of cairo limitation
    at low zoom ratios. This limitation has something to do with the number and
    size of images drawn during a single update. By storing and lower-resolution
    versions of each waveform segment, we can avoid hitting this limitation.

 pitivi/ui/previewer.py |   55 ++++++++++++++++++++++++++++++++++++++---------
 1 files changed, 44 insertions(+), 11 deletions(-)
---
diff --git a/pitivi/ui/previewer.py b/pitivi/ui/previewer.py
index 982f634..7401598 100644
--- a/pitivi/ui/previewer.py
+++ b/pitivi/ui/previewer.py
@@ -461,17 +461,31 @@ class RandomAccessAudioPreviewer(RandomAccessPreviewer):
         self.audioPipeline.set_state(gst.STATE_PLAYING)
 
     def _finishWaveform(self):
+        surfaces = []
         surface = cairo.ImageSurface(cairo.FORMAT_A8,
             self.base_width, self.theight)
         cr = cairo.Context(surface)
-        self._plotWaveform(cr)
+        self._plotWaveform(cr, self.base_width)
         self.audioSink.reset()
-        gobject.idle_add(self._finishThumbnail, surface, self._audio_cur)
 
-    def _plotWaveform(self, cr):
+        for width in [25, 100, 200]:
+            scaled = cairo.ImageSurface(cairo.FORMAT_A8,
+               width, self.theight)
+            cr = cairo.Context(scaled)
+            matrix = cairo.Matrix()
+            matrix.scale(self.base_width/width, 1.0)
+            cr.set_source_surface(surface)
+            cr.get_source().set_matrix(matrix)
+            cr.rectangle(0, 0, width, self.theight)
+            cr.fill()
+            surfaces.append(scaled)
+        surfaces.append(surface)
+        gobject.idle_add(self._finishThumbnail, surfaces, self._audio_cur)
+
+    def _plotWaveform(self, cr, base_width):
         # clear background
         cr.set_source_rgba(1, 1, 1, 0.0)
-        cr.rectangle(0, 0, self.base_width, self.theight)
+        cr.rectangle(0, 0, base_width, self.theight)
         cr.fill()
 
         samples = self.audioSink.samples
@@ -480,7 +494,7 @@ class RandomAccessAudioPreviewer(RandomAccessPreviewer):
             return
 
         # find the samples-per-pixel ratio
-        spp = len(samples) / self.base_width
+        spp = len(samples) / base_width
         if spp == 0:
             spp = 1
         channels = self.audioSink.channels
@@ -509,12 +523,31 @@ class RandomAccessAudioPreviewer(RandomAccessPreviewer):
         cr.stroke()
 
     def _thumbForTime(self, cr, time, x, y):
-        RandomAccessPreviewer._thumbForTime(self, cr, time, x, y)
-        x_scale = float(self.base_width) / self.twidth
-        matrix = cairo.Matrix()
-        matrix.scale(x_scale, 1.0)
-        matrix.translate(-x, -y)
-        cr.get_source().set_matrix(matrix)
+        segment = self._segment_for_time(time)
+        twidth = self.twidth
+        if segment in self._cache:
+            surfaces = self._cache[segment]
+            if twidth > 200:
+                surface = surfaces[3]
+                base_width = self.base_width
+            elif twidth <= 200:
+                surface = surfaces[2]
+                base_width = 200
+            elif twidth <= 100:
+                surface = surfaces[1]
+                base_width = 100
+            elif twidth <= 25:
+                surface = surfaces[0]
+                base_width = 25
+            x_scale = float(base_width) / self.twidth
+            cr.set_source_surface(surface)
+            matrix = cairo.Matrix()
+            matrix.scale(x_scale, 1.0)
+            matrix.translate(-x, -y)
+            cr.get_source().set_matrix(matrix)
+        else:
+            self._requestThumbnail(segment)
+            cr.set_source_rgba(0.0, 0.0, 0.0, 0.0)
 
     def _connectSettings(self, settings):
         RandomAccessPreviewer._connectSettings(self, settings)