# tkspline(3tk) [centos man page]

tkspline(n)Tk Spline - An additional smoothing method for canvas items tkspline(n)__________________________________________________________________________________________________________________________________________________NAME

spline, - additional smoothing method for canvas items.SYNOPSIS

package require Tkspline ... .c create line ...spline ... .c create polygon ...-smoothspline ...-smooth_________________________________________________________________INTRODUCTION

The new option value:spline provides an additional smoothing method to line and polygon canvas items. Spline smoothing will revert to the builtin smoothing method unless the number of points is 3n+1, where n is the number of spline segments. (Normally in polygons this means 3n points because the last point of the spline is understood to be the same as the first in order to close the polygon). In line and polygon items, the curves generated with the standard-smoothtrue option have the following properties: - the curve is always tangential to a straight line between consecutive points. - the curve is only guaranteed to intersect the first and last points of lines. - the curve is not guaranteed to intersect any points of polygons. With-smoothspline (and the right number of coordinates) the curves generated have the following different properties: - the curve is guaranteed to intersect the first point, and every third point after that. - each segment of the curve shares endpoints with the adjacent segments, but is otherwise independent of them. - the curve is guaranteed to be tangential to a line between n and n+1 at point n, and also to a line between n+2 and n+3 at point n+3. - the curve is not guaranteed to be smooth at the junctions between segments unless the shared point and the points either side of it are on a straight line. These alternative properties are useful to some path planning algorithms.-smoothCREDITS

The underlying Bezier code is in John Ousterhout's original canvas widget, this extension just provides an alternate interface to it. The hooks into the canvas are provided by Jan Nijtmans in his "dash" patch.KEYWORDS

spline, line, polygon, bezier, canvas, widgetAUTHOR

John Ellson, ellson@graphviz.orgTk8.0 tkspline(n)

## Check Out this Related Man Page

exspline(3alleg4) Allegro manual exspline(3alleg4)NAME

exspline - Constructing smooth movement paths from spline curves. Allegro game programming library.SYNOPSIS

#include <allegro.h> Example exsplineDESCRIPTION

This program demonstrates the use of spline curves to create smooth paths connecting a number of node points. This can be useful for con- structing realistic motion and animations. The technique is to connect the series of guide points p1..p(n) with spline curves from p1-p2, p2-p3, etc. Each spline must pass though both of its guide points, so they must be used as the first and fourth of the spline control points. The fun bit is coming up with sensible values for the second and third spline control points, such that the spline segments will have equal gradients where they meet. I came up with the following solution: For each guide point p(n), calculate the desired tangent to the curve at that point. I took this to be the vector p(n-1) -> p(n+1), which can easily be calculated with the inverse tangent function, and gives decent looking results. One implication of this is that two dummy guide points are needed at each end of the curve, which are used in the tangent calculations but not connected to the set of splines. Having got these tangents, it becomes fairly easy to calculate the spline control points. For a spline between guide points p(a) and p(b), the second control point should lie along the positive tangent from p(a), and the third control point should lie along the negative tangent from p(b). How far they are placed along these tangents controls the shape of the curve: I found that applying a 'curviness' scaling factor to the distance between p(a) and p(b) works well. One thing to note about splines is that the generated points are not all equidistant. Instead they tend to bunch up nearer to the ends of the spline, which means you will need to apply some fudges to get an object to move at a constant speed. On the other hand, in situations where the curve has a noticeable change of direction at each guide point, the effect can be quite nice because it makes the object slow down for the curve.SEE ALSO

END_OF_MAIN(3alleg4), SCREEN_W(3alleg4), acquire_screen(3alleg4), alert(3alleg4), allegro_error(3alleg4), allegro_init(3alleg4), alle- gro_message(3alleg4), calc_spline(3alleg4), circlefill(3alleg4), clear_keybuf(3alleg4), clear_to_color(3alleg4), desktop_palette(3alleg4), fixatan2(3alleg4), fixcos(3alleg4), fixed(3alleg4), fixmul(3alleg4), fixsin(3alleg4), fixsqrt(3alleg4), fixtof(3alleg4), fixtoi(3alleg4), font(3alleg4), ftofix(3alleg4), install_keyboard(3alleg4), install_mouse(3alleg4), install_timer(3alleg4), itofix(3alleg4), key(3alleg4), keypressed(3alleg4), line(3alleg4), makecol(3alleg4), mouse_b(3alleg4), mouse_x(3alleg4), mouse_y(3alleg4), palette_color(3alleg4), poll_mouse(3alleg4), readkey(3alleg4), release_screen(3alleg4), screen(3alleg4), set_gfx_mode(3alleg4), set_palette(3alleg4), show_mouse(3alleg4), spline(3alleg4), textout_centre_ex(3alleg4), textprintf_centre_ex(3alleg4), textprintf_ex(3alleg4), vsync(3alleg4), xor_mode(3alleg4)Allegroversion 4.4.2 exspline(3alleg4)