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"correct" curve drawing (no artifacts during redraw)

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Interpolation errors still need addressing.
This commit is contained in:
Paul Davis 2014-03-04 21:58:07 -05:00
parent c29d392b0c
commit e6849e9c7e
1 changed files with 29 additions and 31 deletions
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60
libs/canvas/curve.cc
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@ -283,10 +283,15 @@ Curve::map_value (double x) const
void
Curve::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) const
{
if (!_outline || _points.size() < 2) {
if (!_outline || _points.size() < 2 || !_bounding_box) {
return;
}
Rect self = item_to_window (_bounding_box.get());
boost::optional<Rect> d = self.intersection (area);
assert (d);
Rect draw = d.get ();
/* Our approach is to always draw n_segments across our total size.
*
* This is very inefficient if we are asked to only draw a small
@ -294,21 +299,9 @@ Curve::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) const
* with this.
*/
double y;
if (!_bounding_box) {
return;
}
Rect draw = area;
setup_outline_context (context);
/*
double r, g, b;
r = (random() % 255) / 255.0;
g = (random() % 255) / 255.0;
b = (random() % 255) / 255.0;
context->set_source_rgb (r, g, b);
*/
if (_points.size() == 2) {
/* straight line */
@ -320,15 +313,31 @@ Curve::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) const
window_space = item_to_window (_points.back());
context->line_to (window_space.x, window_space.y);
context->stroke ();
} else {
/* curve of at least 3 points */
/* clamp actual draw to area bound by points, rather than our bounding box which is slightly different */
/* x-axis limits of the curve, in window space coordinates */
Duple w1 = item_to_window (Duple (_points.front().x, 0.0));
Duple w2 = item_to_window (Duple (_points.back().x, 0.0));
/* clamp actual draw to area bound by points, rather than our bounding box which is slightly different */
context->save ();
context->rectangle (draw.x0, draw.y0, draw.width(), draw.height());
context->clip ();
/* expand drawing area by several pixels on each side to avoid cairo stroking effects at the boundary.
they will still occur, but cairo's clipping will hide them.
*/
draw = draw.expand (4.0);
/* now clip it to the actual points in the curve */
if (draw.x0 < w1.x) {
draw.x0 = w1.x;
}
@ -337,8 +346,6 @@ Curve::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) const
draw.x1 = w2.x;
}
std::cerr << "Draw " << draw << " win-x = " << w1 << " .. " << w2 << std::endl;
/* full width of the curve */
const double xextent = _points.back().x - _points.front().x;
/* Determine where the first drawn point will be */
@ -348,22 +355,14 @@ Curve::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) const
const uint32_t pixels = draw.width ();
Duple window_space;
#if 1
std::cerr << "begin draw at " << draw.x0 << " (" << item_space.x << ") which is " << xfract_offset << " into " << w1.x << " .. " << w2.x
<< " I = " << _points.front().x << " .. " << _points.back().x
<< std::endl;
#endif
/* draw the first point */
std::cerr << this << " redraw " << pixels << " pixels from " << draw.x0 << " .. " << draw.x0 + pixels << std::endl;
for (uint32_t pixel = 0; pixel < pixels; ++pixel) {
/* fractional distance into the total horizontal extent of the curve */
double xfract = xfract_offset + (pixel / xextent);
/* compute vertical coordinate (item-space) at that location */
y = map_value (xfract);
double y = map_value (xfract);
/* convert to window space for drawing */
window_space = item_to_window (Duple (0.0, y)); /* x-value is irrelevant */
@ -377,12 +376,11 @@ Curve::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) const
} else {
context->line_to (window_space.x, window_space.y);
}
std::cerr << window_space << ' ';
}
std::cerr << std::endl;
}
context->stroke ();
context->stroke ();
context->restore ();
}
#if 0
/* add points */