flying-balls/gravity.cc

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#include "gravity.h"
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#include "game.h"
#include "polygons.h"
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#include <cmath>
#include <gtk/gtk.h>
#include <sstream>
#include <string>
static const double constant_field_increment = 1.0;
static const double newton_field_increment = 1000.0;
static vec2d g{.x = 0, .y = 20};
static double g_r = 50;
static double g_g = 10000000;
static int constant_field = 1;
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void gravity_constant_field(double x, double y) {
constant_field = 1;
g.x = x;
g.y = y;
}
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void gravity_newton_field(double r, double g) {
constant_field = 0;
g_r = r;
g_g = g;
}
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void gravity_draw(cairo_t* cr) {
if (constant_field) {
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cairo_save(cr);
cairo_new_path(cr);
cairo_move_to(cr, width / 2, height / 2);
cairo_line_to(cr, width / 2 + g.x, height / 2 + g.y);
cairo_set_source_rgb(cr, 1.0, 1.0, 1.0);
cairo_set_line_width(cr, 1.0);
cairo_stroke(cr);
cairo_arc(cr, width / 2 + g.x, height / 2 + g.y, 3, 0, 2 * M_PI);
cairo_fill(cr);
cairo_restore(cr);
} else {
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std::ostringstream output;
output << (g_g / 1000) << "K";
cairo_save(cr);
cairo_set_source_rgb(cr, 1.0, 1.0, 1.0);
cairo_select_font_face(cr,
"sans-serif",
CAIRO_FONT_SLANT_NORMAL,
CAIRO_FONT_WEIGHT_NORMAL);
cairo_set_font_size(cr, 16);
std::string output_str = output.str();
cairo_text_extents_t extent;
cairo_text_extents(cr, output_str.c_str(), &extent);
cairo_move_to(
cr, width / 2 - extent.width / 2, height / 2 + extent.height / 2);
cairo_show_text(cr, output_str.c_str());
cairo_restore(cr);
}
}
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void gravity_draw_visible_field(cairo_t* cr) {
if (!constant_field) {
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cairo_save(cr);
cairo_set_source_rgb(cr, 1.0, 1.0, 1.0);
cairo_new_path(cr);
cairo_arc(cr, width / 2, height / 2, g_r, 0, 2 * M_PI);
cairo_set_line_width(cr, 3.0);
cairo_stroke(cr);
cairo_restore(cr);
}
}
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void gravity_change(double dx, double dy) {
if (constant_field) {
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g.x += dx * constant_field_increment;
g.y += dy * constant_field_increment;
} else {
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g_r += dx;
g_g -= dy * newton_field_increment;
}
}
vec2d gravity_vector(const polygon* p) {
if (constant_field) {
return g;
} else {
vec2d b_c = vec2d{width / 2.0, height / 2.0} - p->centroid();
double r2 = vec2d::dot(b_c, b_c);
if (r2 < g_r * g_r)
return vec2d{0, 0};
else
return g_g / r2 / sqrt(r2) * b_c;
}
}
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vec2d gravity_vector(const ball* b) {
if (constant_field) {
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return g;
} else {
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vec2d b_c = vec2d{width / 2.0, height / 2.0} - b->position;
double r2 = vec2d::dot(b_c, b_c);
if (r2 < g_r * g_r)
return vec2d{0, 0};
else
return g_g / r2 / sqrt(r2) * b_c;
}
}
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void gravity_collisions(ball* begin, ball* end) {
if (constant_field)
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return;
for (ball* b = begin; b != end; ++b) {
vec2d b_c = b->position - vec2d{width / 2.0, height / 2.0};
double d2 = vec2d::dot(b_c, b_c);
double r = b->radius + g_r;
if (d2 <= r * r) {
double d = sqrt(d2);
if (d <= b->radius)
b->position = vec2d{width / 2.0, height / 2.0 + r};
else
b->position += (r - d) / d * b_c;
double f = vec2d::dot(b->velocity, b_c);
if (f < 0) {
f /= d2;
b->velocity -= 2 * f * b_c;
}
}
}
}