void turtle_draw_circle(int x0, int y0, int radius)
{
// implementation based on midpoint circle algorithm:
// https://en.wikipedia.org/wiki/Midpoint_circle_algorithm
int x = radius;
int y = 0;
int switch_criteria = 1 - x;
if (main_turtle.filled) {
turtle_fill_circle(x0, y0, radius);
}
while (x >= y) {
turtle_draw_pixel( x + x0, y + y0);
turtle_draw_pixel( y + x0, x + y0);
turtle_draw_pixel(-x + x0, y + y0);
turtle_draw_pixel(-y + x0, x + y0);
turtle_draw_pixel(-x + x0, -y + y0);
turtle_draw_pixel(-y + x0, -x + y0);
turtle_draw_pixel( x + x0, -y + y0);
turtle_draw_pixel( y + x0, -x + y0);
y++;
if (switch_criteria <= 0) {
switch_criteria += 2 * y + 1; // no x-coordinate change
} else {
x--;
switch_criteria += 2 * (y - x) + 1;
}
}
}
void turtle_draw_line(int x0, int y0, int x1, int y1)
{
// uses a variant of Bresenham's line algorithm:
// https://en.wikipedia.org/wiki/Talk:Bresenham%27s_line_algorithm
int absX = ABS(x1-x0); // absolute value of coordinate distances
int absY = ABS(y1-y0);
int offX = x0<x1 ? 1 : -1; // line-drawing direction offsets
int offY = y0<y1 ? 1 : -1;
int x = x0; // incremental location
int y = y0;
int err;
turtle_draw_pixel(x, y);
if (absX > absY) {
// line is more horizontal; increment along x-axis
err = absX / 2;
while (x != x1) {
err = err - absY;
if (err < 0) {
y += offY;
err += absX;
}
x += offX;
turtle_draw_pixel(x,y);
}
} else {
// line is more vertical; increment along y-axis
err = absY / 2;
while (y != y1) {
err = err - absX;
if (err < 0) {
x += offX;
err += absY;
}
y += offY;
turtle_draw_pixel(x,y);
}
}
}
void turtle_draw_int(int value)
{
// calculate number of digits to draw
int ndigits = 1;
if (value > 9) {
ndigits = (int)(ceil(log10(value)));
}
// draw each digit
for (int i=ndigits-1; i>=0; i--) {
int digit = value % 10;
for (int y=0; y<5; y++) {
for (int x=0; x<4; x++) {
if (TURTLE_DIGITS[digit][y*4+x] == 1) {
turtle_draw_pixel(main_turtle.xpos + i*5 + x, main_turtle.ypos - y);
}
}
}
value = value / 10;
}
}
void turtle_dot()
{
// draw a pixel at the current location, regardless of pen status
turtle_draw_pixel((int)round(main_turtle.xpos),
(int)round(main_turtle.ypos));
}
