bresenham_circle.cpp

#include <stdio.h>

#define WIDTH 320
#define HEIGHT 200

int main(int argc, char** argv)
{
	char Pixels[HEIGHT][WIDTH] = {};
	short Cx = 160;
	short Cy = 100;
	short R = 30;
	short X = -R;
	short Y = 0;
	short Ep = 0;
	char* Cursor = &Pixels[Cx][Cy];
	// si = X
	// di = Y
	// bx = Ep
	// bp is a scratch register (we don't need a frame pointer)
	// this leaves ax,cx,dx free for pixel fill (and bp is available too)

	// jmp loop_test
	// loop_top:
	while (X + Y < 0) {
		Cursor[Y * WIDTH + X] = 1;
		Cursor[Y * WIDTH - X] = 1;
		Cursor[-Y * WIDTH + X] = 1;
		Cursor[-Y * WIDTH - X] = 1;
		Cursor[X * WIDTH + Y] = 1;
		Cursor[X * WIDTH - Y] = 1;
		Cursor[-X * WIDTH + Y] = 1;
		Cursor[-X * WIDTH - Y] = 1;

		// lea bx,[bx+di+1]
		// add bx,di
		Ep += (Y << 1) + 1;
		// mov bp,bx
		// add bp,si
		// jg no_x_inc
		if (Ep + X > 0) {
			// lea bx,[bp+si]
			Ep += X << 1;
			// inc si
			++X;
		}
		// no_x_inc:
		// inc di
		++Y;
		// loop_test:
		// mov bp,si
		// add bp,di
		// jl loop_top
	}
	for (int Y = 0; Y < HEIGHT; ++Y) {
		for (int X = 0; X < WIDTH; ++X) {
			printf(Pixels[Y][X] ? "*" : ".");
		}
		printf("\n");
	}
}