Bresenham for VB

triproc.c

#include "libgccvb/libgccvb.h"
#include "gamectl.h"
#include <limits.h>

void draw_line(short start_x, short start_y, short start_z, \
	short end_x, short end_y, short end_z);
void inline plot_point(short x, short y, short z);
/* void inline convert_octant(short * dx, short * dy, short * z); */
int sign(int i);
int iabs(int i);
//int swap(short * x, short * y);

void triangle_mainproc()
{
	WA[31].head = WRLD_END;
	vbDisplayShow();
	
	while(!(vbPadKeyDown()))
	{
		//int i;
		/* for(i = 0; i < 384; i++)
		{
			plot_point(i, i, i/12);
		} */
		//Synchronize with display
		
		//Draw lines until VIP says that "need to draw"
		
		draw_line(0, 0, 0, 383, 223, 0);
		draw_line(0, 0, 0, 383, 223, 0);
		draw_line(0, 0, 0, 383, 223, 0);
		
		//draw_line(100, 100, 0, 150, 200, 0);
		//draw_line(150, 200, 0, 150, 150, 0);
		//draw_line(150, 150, 0, 100, 100, 0);
		//draw_line(250, 50, 0, 100, 100, 0);
		//draw_line(200, 75, 0, 100, 100, 0);
		//draw_line(0, 150, 0, 100, 100, 0);
		//draw_line(100, 100, 0, 125, 220, 0);
		//draw_line(200, 150, 0, 100, 100, 0);
		//draw_line(100, 100, 0, 50, 200, 0);
		//draw_line(0, 25, 0, 200, 150, 0);
		//draw_line(50, 150, 0, 50, 200, 0);
	}
	 
	
	vbDisplayHide();
	jump_to_reset();
}

//Use Bresenham's algorithm
void draw_line(short start_x, short start_y, short start_z, \
	short end_x, short end_y, short end_z)
{
	int count;
	int do_swap = 0;
	long error = 0;
	short dx;
	short dy; 
	short di; /* Change in independent var */
	short dd; /* Change in dependent var */
	short curr_dv, start_iv, end_iv, start_dv, end_dv;
	//short * curr_x, * curr_y;
	
	dx = iabs(end_x - start_x);
	dy = iabs(end_y - start_y); 
	
	/* If y changes at a faster rate than y, do all calculations relative to
	y (i.e. y is independent var), and reverse vars when plotting. */
	if(dx < dy)
	{
		do_swap = 1;
		di = dy;
		dd = dx;
		start_iv = start_y;
		end_iv = end_y;
		start_dv = start_x;
		end_dv = end_x;
		curr_dv = start_x;
	}
	else
	{
		do_swap = 0;
		di = dx;
		dd = dy;
		start_iv = start_x;
		end_iv = end_x;
		start_dv = start_y;
		end_dv = end_y;
		curr_dv = start_y;
	}
	
	error = 2*dd - di;
	
	plot_point(start_x, start_y, 0);
	
	if(end_iv > start_iv)
	{
		for(count = (start_iv + 1); count <= end_iv; count++)
		{
			if(error > 0)
			{
				if(end_dv > start_dv)
				{
					curr_dv = curr_dv + 1;
				}
				else
				{
					curr_dv = curr_dv - 1;
				}
					
				error = error + (2*dd - 2*di);
			}
			else
			{
				error = error + 2*dd;
			}
			
			if(do_swap)
			{
				plot_point(curr_dv, count, 0);
			}
			else
			{
				plot_point(count, curr_dv, 0);
			}
		}
	}
	else if(end_iv < start_iv)
	{
		for(count = (start_iv - 1); count >= end_iv; count--)
		{
			if(error > 0)
			{
				if(end_dv > start_dv)
				{
					curr_dv = curr_dv + 1;
				}
				else
				{
					curr_dv = curr_dv - 1;
				}
					
				error = error + (2*dd - 2*di);
			}
			else
			{
				error = error + 2*dd;
			}
			
			if(do_swap)
			{
				plot_point(curr_dv, count, 0);
			}
			else
			{
				plot_point(count, curr_dv, 0);
			}
		}
	}
	else /* Vertical or Horizontal Line. */
	{
		for(count = start_dv; count <= end_dv; count++)
		{
			if(do_swap)
			{
				plot_point(count, start_iv, 0);
			}
			else
			{
				plot_point(start_iv, count, 0);
			}
		}
	}
}

void inline plot_point(short x, short y, short z)
{
	short y_bias = 2*(y & 0x0F); /* Multiply by 2 b/c 2 bits == 1 pixel */
	
	short rx_offs = 16*(x + z); /* 64 bytes (half-words) per column == 16 longs */
	short lx_offs = 16*(x - z); /* 64 bytes (half-words) per column == 16 longs */
	short y_offs = y >> 4; /* 16 pixels per 4 bytes (doubleword). */
	short lframe_pos = lx_offs + y_offs;
	short rframe_pos = rx_offs + y_offs;
		
	(* (L_FRAME0 + lframe_pos)) |= 0x0003uL << y_bias;
	(* (L_FRAME1 + lframe_pos)) |= 0x0003uL << y_bias;
	(* (R_FRAME0 + rframe_pos)) |= 0x0003uL << y_bias;
	(* (R_FRAME1 + rframe_pos)) |= 0x0003uL << y_bias;
	
	/* (* (L_FRAME0 + lframe_pos)) = 0x0003uL << y_bias;
	(* (L_FRAME1 + lframe_pos)) = 0x0003uL << y_bias;
	(* (R_FRAME0 + rframe_pos)) = 0x0003uL << y_bias;
	(* (R_FRAME1 + rframe_pos)) = 0x0003uL << y_bias; */
	
}

int sign(int i)
{
	return i > 0 ? 1 : -1;
}

/* Relies on twos-complement arithmetic. */
int iabs(int i)
{
	return i >= 0 ? i : -i;
}

/* void inline convert_octant(short * dx, short * dy, short * z)
{
	if(	
	
} */