no-reply@allegro.cc (Fred58) — Mon, 16 Jul 2012 12:23:26 +0000

hello,

i'm looking for examples of code for functions because i don't understand the
int points_stride and int num_segments parameters :

void al_draw_ribbon(const float *points, int points_stride, ALLEGRO_COLOR color,
float thickness, int num_segments)

void al_calculate_ribbon(float* dest, int dest_stride, const float *points,
int points_stride, float thickness, int num_segments)

void al_calculate_spline(float* dest, int stride, float points[8],
float thickness, int num_segments)

Thank very much
F

no-reply@allegro.cc (SiegeLord) — Mon, 16 Jul 2012 18:02:44 +0000

Here's a quick example. I note that num_segments is a wrong name for that parameter: it should be num_corners or num_points perhaps. The stride parameters allow you to use structs that are not just pairs of floats when the functions ask for points.

#SelectExpand
  1#include 
  2#include 
  3
  4int main()
  5{
al_init();
al_init_primitives_addon();
auto disp = al_create_display(800, 600);
auto queue = al_create_event_queue();
al_register_event_source(queue, al_get_display_event_source(disp));
al_clear_to_color(al_map_rgb_f(0, 0, 0));

struct MyPoint
{
  float x, y;
  int something_else;
};

const size_t num_points1 = 5;
MyPoint points1[5] = 
{
  {100, 100, 0},
  {100, 150, 0},
  {200, 200, 0},
  {200, 300, 0},
  {100, 500, 0}
};

al_draw_ribbon((float*)points1, sizeof(MyPoint), al_map_rgb_f(1, 0, 0.5), 10, num_points1);

const size_t num_points2 = num_points1 * 2;
auto points2 = new MyPoint[num_points2];

al_calculate_ribbon((float*)points2, sizeof(MyPoint), (float*)points1, sizeof(MyPoint), 30, num_points1);

for(size_t ii = 0; ii < num_points2; ii++)
  al_draw_filled_circle(points2[ii].x, points2[ii].y, 5, al_map_rgb_f(1, 0.5, 0));

float spline_control_points[8] = 
{
  400, 100,
  500, 200,
  300, 400,
  400, 500
};

al_calculate_spline((float*)points2, sizeof(MyPoint), spline_control_points, 30, num_points1);

for(size_t ii = 0; ii < num_points2; ii++)
  al_draw_filled_circle(points2[ii].x, points2[ii].y, 5, al_map_rgb_f(0.5, 1, 0));

al_flip_display();
ALLEGRO_EVENT ev;
al_wait_for_event(queue, &ev);

delete[] points2;
 57}

no-reply@allegro.cc (Fred58) — Sat, 21 Jul 2012 18:21:14 +0000

Thank you very much for this example of code.
Very usefull for understanding !

example of code for al_draw_ribbon, al_calculate_spline/ribbon