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fix x-fade drawing

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Catmull-Rom curve samples are not equally spaced on the x-axis.
Furthermore, Curve::map_value() is not needed, cairo line_to
already interpolates.
This commit is contained in:
Robin Gareus 2014-05-26 17:02:21 +02:00
parent a0037ee2d8
commit 791c668756
2 changed files with 19 additions and 58 deletions
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1
libs/canvas/canvas/curve.h
View File

@ -50,7 +50,6 @@ public:
uint32_t points_per_segment;
SplineType curve_type;
double map_value (double) const;
void interpolate ();
static void interpolate (const Points& coordinates, uint32_t points_per_segment, SplineType, bool closed, Points& results);

76
libs/canvas/curve.cc
View File

@ -272,34 +272,6 @@ Curve::interpolate (const Points& coordinates, uint32_t points_per_segment, Spli
}
}
/** Given a fractional position within the x-axis range of the
* curve, return the corresponding y-axis value
*/
double
Curve::map_value (double x) const
{
if (x > 0.0 && x < 1.0) {
double f;
Points::size_type index;
/* linearly interpolate between two of our smoothed "samples"
*/
x = x * (n_samples - 1);
index = (Points::size_type) x; // XXX: should we explicitly use floor()?
f = x - index;
return (1.0 - f) * samples[index].y + f * samples[index+1].y;
} else if (x >= 1.0) {
return samples.back().y;
} else {
return samples.front().y;
}
}
void
Curve::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) const
{
@ -366,36 +338,26 @@ Curve::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) const
draw.x1 = w2.x;
}
/* full width of the curve */
const double xextent = _points.back().x - _points.front().x;
/* Determine where the first drawn point will be */
Duple item_space = window_to_item (Duple (draw.x0, 0)); /* y value is irrelevant */
/* determine the fractional offset of this location into the overall extent of the curve */
const double xfract_offset = (item_space.x - _points.front().x)/xextent;
const uint32_t pixels = draw.width ();
/* find left and right-most sample */
Points::size_type left = 0;
Points::size_type right = n_samples;
for (Points::size_type idx = 0; idx < n_samples - 1; ++idx) {
left = idx;
if (samples[idx].x >= draw.x0) break;
}
for (Points::size_type idx = n_samples; idx > left + 1; --idx) {
if (samples[idx].x <= draw.x1) break;
right = idx;
}
/* draw line between samples */
Duple window_space;
/* draw the first point */
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 */
double y = map_value (xfract);
/* convert to window space for drawing */
window_space = item_to_window (Duple (0.0, y)); /* x-value is irrelevant */
/* we are moving across the draw area pixel-by-pixel */
window_space.x = draw.x0 + pixel;
/* plot this point */
if (pixel == 0) {
context->move_to (window_space.x, window_space.y);
} else {
context->line_to (window_space.x, window_space.y);
}
window_space = item_to_window (Duple (samples[left].x, samples[left].y));
context->move_to (window_space.x, window_space.y);
for (uint32_t idx = left + 1; idx < right; ++idx) {
window_space = item_to_window (Duple (samples[idx].x, samples[idx].y));
context->line_to (window_space.x, window_space.y);
}
context->stroke ();