ardour/livetrax
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stop pixel jitter when changing waveview height.

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To avoid pixel jitter, the top and bottom of each line in the waveview must be computed together in a single computation,
rather than independently.

Also, remove various height corrections and cairo translations that are not necessary or relevant anymore. A subsequent
commit for the GUI will pick up on this work to get the appearance completely correct
This commit is contained in:
Paul Davis 2015-06-19 08:14:02 -04:00
parent 1043357cc9
commit 8491a015e3
2 changed files with 102 additions and 75 deletions
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14
libs/canvas/canvas/wave_view.h
View File

@ -364,7 +364,19 @@ public:
boost::shared_ptr<WaveViewCache::Entry> get_image (framepos_t start, framepos_t end, bool& full_image) const;
boost::shared_ptr<WaveViewCache::Entry> get_image_from_cache (framepos_t start, framepos_t end, bool& full_image) const;
ArdourCanvas::Coord y_extent (double, bool) const;
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) {}
};
ArdourCanvas::Coord y_extent (double) const;
void compute_tips (ARDOUR::PeakData const & peak, LineTips& tips) const;
void draw_image (Cairo::RefPtr<Cairo::ImageSurface>&, ARDOUR::PeakData*, int n_peaks, boost::shared_ptr<WaveViewThreadRequest>) const;
void draw_absent_image (Cairo::RefPtr<Cairo::ImageSurface>&, ARDOUR::PeakData*, int) const;

163
libs/canvas/wave_view.cc
View File

@ -252,41 +252,66 @@ WaveView::invalidate_image_cache ()
_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
@ -321,16 +346,6 @@ 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;
@ -387,8 +402,8 @@ 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;
@ -404,8 +419,8 @@ 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;
}
@ -417,34 +432,34 @@ 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;
}
@ -457,8 +472,7 @@ 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;
}
@ -479,16 +493,16 @@ 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.
@ -550,7 +564,7 @@ WaveView::draw_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peak
outline_context->stroke ();
} else {
const double height_2 = (_height - 2.5) * .5;
const double height_2 = _height * .5;
for (int i = 0; i < n_peaks; ++i) {
@ -560,6 +574,7 @@ 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) {
@ -575,7 +590,7 @@ WaveView::draw_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peak
}
}
/* zero line */
/* zero line, show only if there is enough spread */
if (tips[i].spread >= 5.0 && show_zero_line()) {
zero_context->move_to (i, floor(height_2));
@ -600,12 +615,12 @@ WaveView::draw_image (Cairo::RefPtr<Cairo::ImageSurface>& image, PeakData* _peak
}
if (!clipped) {
outline_context->move_to (i, tips[i].bot + 1.0);
/* normal lower terminal dot */
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 {