PicoGraphics Implementation of Arc, Pie and Fast Trigonometry

[thinkier]

Hi, I implemented the maths for drawing arcs and pies for one of my projects. I thought it would be helpful to contribute this upstream too.

This works like normal trigonometry except it's degrees based (due to performance hits with float related operations). With this particular implementation, the discrete steps are 1 degree.

Example

#include <cmath>
#include <cstdlib>

#include "drivers/st7789/st7789.hpp"
#include "libraries/pico_graphics/pico_graphics.hpp"

using namespace pimoroni;

const int WIDTH = 240;
const int HEIGHT = 240;

ST7789 st7789(WIDTH, HEIGHT, ROTATE_0, true, get_spi_pins(BG_SPI_FRONT));
PicoGraphics_PenRGB332 graphics(st7789.width, st7789.height, nullptr);

Pen blk = graphics.create_pen(0x00, 0x00, 0x00);
Pen wht = graphics.create_pen(0xFF, 0xFF, 0xFF);
Pen red = graphics.create_pen(0xFF, 0x00, 0x00);
Pen orn = graphics.create_pen(0xFF, 0xA5, 0x00);
Pen ylw = graphics.create_pen(0xFF, 0xFF, 0x00);
Pen grn = graphics.create_pen(0x00, 0x80, 0x00);
Pen blu = graphics.create_pen(0x00, 0x00, 0xFF);
Pen pur = graphics.create_pen(0x4B, 0x00, 0x82);

void rainbow(int8_t r, int8_t w) {
    graphics.arc(
        Point(WIDTH / 2, HEIGHT / 2),
        Point(WIDTH / 2 + r, HEIGHT / 2),
        180,
        w
    );
}

int main() {
    st7789.set_backlight(255);
    Point c(120, 120);

    graphics.set_pen(blk);
    graphics.clear();

    // Demo of poly impl (rainbow)
    graphics.set_pen(red);
    rainbow(120, 10);
    graphics.set_pen(orn);
    rainbow(110, 10);
    graphics.set_pen(ylw);
    rainbow(100, 10);
    graphics.set_pen(grn);
    rainbow(90, 10);
    graphics.set_pen(blu);
    rainbow(80, 10);
    graphics.set_pen(pur);
    rainbow(70, 10);

    graphics.set_pen(wht);
    // Demo of pie
    graphics.arc(c, Point(180, 180), -90, 85);
    // Demo of line arc
    for (int i = 0; i < 6; i++) {
        graphics.arc(c, Point(239 - (i * 10), 120), -180);
    }

    st7789.update(&graphics);
}

Demo

[thinkier]

8ed7fae should address the CI failures.

[Gadgetoid]

Thank you, your demo shot looks incredible! This could be really useful. I probably wont have the time to give this the attention it deserves until the new year, but it's on my radar.

[Gadgetoid]

This might have been entirely supplanted by PicoVector - #783 - which, with a basic walk around the perimeter of two circles of "r" and "r - arc_thickness", can produce similar results. I posted an example to this end here - #783 (comment)

Does make me wonder if PicoVector should have an explicit arc function. It's fertile ground for all-the-shapes.

[Gadgetoid]

The new, updated PicoVector does have an explicit arc function, but it's still slowly trundling through the pipeline.

Experimental builds are available here, but there is no documentation... yet - #1019

Since PicoVector can use anti-aliasing, arcs, circles and everything else looks so much nicer!