Commander X16/KickC circle.

// Circle.kc
import "vera"

char j = 16;

void main() {

    vpoke(15,VERA_DC_VIDEO,1);
    vpoke(15,VERA_DC_HSCALE,64);
    vpoke(15,VERA_DC_VSCALE,64);

    vpoke(15,VERA_LAYER1,0);
    vpoke(15,VERA_LAYER0,(7 << 5) | 1);

    vpoke(15,VERA_L0_CTRL1,%00000000);

    vpoke(15,VERA_L0_TILE_BASE_L,0);
    vpoke(15,VERA_L0_TILE_BASE_H,0);

    vaddr(0x10,0x0000);

    for (dword i = 0; i < (320*239); i++) {
        *VERA_ADDR_DATA0 = 0;
    }

    for (int i = 5; i < 200; i += 1) {
        circle(160,100,i);
        j++;
    }


    do {} while (1);
}

void circle(int xc, int yc, int r) {
    int x = 0;
    int y = r;
    int p = 3-(r << 1);

    for(int x = 0; x <= y; x ++) {
        if(p < 0) {
            p = p + (x << 2) + 6;
        } else {
            y=y-1;
            p = p + ((x-y) << 2) + 10;
        }

        plot(xc+x,yc-y);
        plot(xc-x,yc-y);
        plot(xc+x,yc+y);
        plot(xc-x,yc+y);
        plot(xc+y,yc-x);
        plot(xc-y,yc-x);
        plot(xc+y,yc+x);
        plot(xc-y,yc+x);
    }
}

void plot(int x, int y) {
    if (x < 0 || x >= 320 || y < 0 || y >= 200) {
        return; // bounds check
    }
    word z = (word) y * 320;
    vpoke(0,(word) x+z, j);
}

-----8<--- split here ---8<-----

// Vera.kc
const char* VERA_ADDR_LO = 0x9f20;
const char* VERA_ADDR_MID = 0x9f21;
const char* VERA_ADDR_HI = 0x9f22;
const char* VERA_ADDR_INC = 0x9f22;
const char* VERA_ADDR_DATA0 = 0x9f23;
const char* VERA_ADDR_DATA1 = 0x9f24;
const char* VERA_CTRL = 0x9f25;

const word VERA_DC_VIDEO = 0x0000;
const word VERA_DC_HSCALE = 0x0001;
const word VERA_DC_VSCALE = 0x0002;
const word VERA_DC_BORDER_COLOR = 0x0003;
const word VERA_DC_HSTART_L = 0x0004;
const word VERA_DC_HSTOP_L = 0x0005;
const word VERA_DC_VSTART_L = 0x0006;
const word VERA_DC_VSTOP_L = 0x0007;
const word VERA_DC_STARTSTOP_H = 0x0008;
const word VERA_DC_IRQ_LINE_L = 0x0009;
const word VERA_DC_IRQ_LINE_H = 0x000a;

const word VERA_LAYER0 = 0x2000;
const word VERA_L0_CTRL1 = 0x2001;
const word VERA_L0_TILE_BASE_L = 0x2004;
const word VERA_L0_TILE_BASE_H = 0x2005;
const word VERA_LAYER1 = 0x3000;
const word VERA_L1_CTRL1 = 0x3001;
const word VERA_L1_TILE_BASE_L = 0x3004;
const word VERA_L1_TILE_BASE_H = 0x3005;

void vaddr(char bank, word offset) {
    *VERA_ADDR_LO = (char) offset;
    *VERA_ADDR_MID = (char) (offset >> 8);
    *VERA_ADDR_HI = bank;
}

void vpoke(char bank, word offset, char value) {
    *VERA_ADDR_LO = (char) offset;
    *VERA_ADDR_MID = (char) (offset >> 8);
    *VERA_ADDR_HI = bank;
    *VERA_ADDR_DATA0 = value;
}

char vpeek(char bank, word offset) {
    *VERA_ADDR_LO = (char) offset;
    *VERA_ADDR_MID = (char) (offset >> 8);
    *VERA_ADDR_HI = bank;
    return *VERA_ADDR_DATA0;
}