lines

[Dio]

How do I draw lines? Um, I should probably clarify. Draw a line using PSET. Just like MS.
When I try I screw it up. So how does MS do it when I ask them to draw a line? Thanks.

[Agamemnus]

The "Bresenham" line algorithm, my friend. Can also draw circles if yer smart..

SUB bline (x, y, x2, y2)
dx = x2 - x
dy = y2 - y
IF dy < 0 THEN dy = -dy: yinc = -1 ELSE xinc = 1
IF dx < 0 THEN dx = -dx: xinc = -1 ELSE yinc = 1
IF dx > dy THEN
d1 = dy + dy - dx - dx
d = d1 + dx
d0 = d + dx
DO
IF x = x2 THEN EXIT DO
x = x + xinc
IF d < 0 THEN d = d + d0 ELSE d = d + d1: y = y + yinc
PSET (x, y)
LOOP
ELSE
d1 = dx + dx - dy - dy
d = d1 + dy
d0 = d + dy
DO
IF y = y2 THEN EXIT DO
y = y + yinc
IF d < 0 THEN d = d + d0 ELSE d = d + d1
x = x + xinc
PSET (x, y)
LOOP
END IF
END SUB

[Dio]

:???: same coordinates:

Code:

screen 13,,,1
x = 30
y = 45
x2 = 70
y2 = 140
line (30,45)-(70,140),4
dx = x2 - x
dy = y2 - y
IF dy < 0 THEN dy = -dy: yinc = -1 ELSE xinc = 1
IF dx < 0 THEN dx = -dx: xinc = -1 ELSE yinc = 1
IF dx > dy THEN
d1 = dy + dy - dx - dx
d = d1 + dx
d0 = d + dx
DO
IF x = x2 THEN EXIT DO
x = x + xinc
IF d < 0 THEN d = d + d0 ELSE d = d + d1: y = y + yinc
PSET (x, y)
LOOP
ELSE
d1 = dx + dx - dy - dy
d = d1 + dy
d0 = d + dy
DO
IF y = y2 THEN EXIT DO
y = y + yinc
IF d < 0 THEN d = d + d0 ELSE d = d + d1
x = x + xinc
PSET (x, y)
LOOP
END IF
sleep

[Ralph]

A little simpler?

Code:

'create a straight line from P1 to P2
'P1(x1,y1)
'P2(x2,y2)
x1 = 10: y1 = 20
x2 = 100: y2 = 150
dx = 1
dy = dx * (y2 - y1) / (x2 - x1)

y = y1
SCREEN 13
FOR x = x1 TO y1
  PSET (x, y), 15
  y = y + 1
NEXT x

[Dio]

Alright, look people, it’s not that hard. I wanna know how do draws lines identical to how MS or whoever draw lines. That means I enter the first set of coordinates then the second, and the line gets drawn. Unless the code needed is ten thousand lines long, and a hundred libs involved, it shouldn’t be that hard. Just say ‘I don’t know” and I’ll stop asking.
I mean, I appreciate the help (in this case, Ralph and Agamemnus) but it just seems like no matter what I ask for or how I articulate it, I never seem to get the results I ask for. “I need code that draws lines” couldn’t be simpler; one of the most basic functions in QBASIC and other crude primitive graphical programming languages and still, no one can give me the right answer. This is why I hardly ask questions, because you people employ sort of passive aggressive attack on my mind. Do you guys go to another forum and mock me, keeping an open log of my mental distress. Placing bets on when I’ll snap. See on the news that some kid from San Diego when on a killing spree.

Again, I appreciate the help, but I feel like I’m a lab rat in some psychology experiment
Agamemnus, the code you showed me almost worked. And Ralph, all I did was change x1 from 10 to 106. and it rendered your code completely useless. And what did I do? Added one number; A 8-bit change is it? And it didn’t even draw a single pixel. I mean, do you guys even test the code that you post? At all?

Look, I’m not a very good programmer, and I have at least five or six more, different, questions I could ask but I don’t for this very reason. But this time I thought, “I’m just asking how to draw lines, there is no way to mess this one up… it’s impossible!” but I was wrong.

And this extends to all my other threads in which I ask questions by the way. Not just this one and you guys (both of you)

So if there is anybody that isn’t to incredibly pissed at me, what is the code to draw lines?

Thank you for letting me rant my built up frustrations.

[Radical Raccoon]

Here's something I coded not too long ago to draw a line in a sprite editor I am working on. It's in C'ish syntax though...

[syntax="C"]
public void DrawLine(Sprite sprite, int color)
{
double slope = (double)(y2 - y1) / (double)(x2 - x1);

double x = (double)this.x1+0.5;
double y = (double)this.y1+0.5;

if(Math.Abs(slope) > 1)
{
slope = (double)(x2 - x1) / (double)(y2 - y1);
if(this.y1 < this.y2)
{
while((int)y <= this.y2)
{
sprite[(int)x, (int)y] = color;
y += 1;
x += slope;
}
}
else
{
while((int)y >= this.y2)
{
sprite[(int)x, (int)y] = color;
y -= 1;
x -= slope;
}
}
}
else
{
if(this.x1 < this.x2)
{
while((int)x <= this.x2)
{
sprite[(int)x, (int)y] = color;
x += 1;
y += slope;
}
}
else
{
while((int)x >= this.x2)
{
sprite[(int)x, (int)y] = color;
x -= 1;
y -= slope;
}
}
}
}
[/syntax]
You should be able to interpret this to basic. It shouldn't be too hard. If you need help, just ask and I'll do it for you.

Oh, yeah:

this.x1, this.y1 = starting coordinate
this.x2, this.y2 = ending coordinate

[axipher]

Here's the transalated code with a little example for you:

Code:

SUB DrawLine(Sprite AS ANY PTR, colour AS INTEGER, _
            x1 as integer, y1 as integer, _
            x2 as integer, y2 as integer)
    DIM AS DOUBLE slope,x,y
    slope = (y2 - y1) / (x2 - x1)
    
    x = x1+0.5
    y = y1+0.5
    
    IF (ABS(slope) > 1) THEN
        
        slope = (x2 - x1) / (y2 - y1)
        IF (y1 < y2) THEN
            
            WHILE (INT(y) <= y2)
                
                PSET sprite,(INT(x),INT(y)),colour
                y += 1
                x += slope
            WEND
            
        ELSE
            
            WHILE (INT(y) >= y2)
                
                PSET sprite,(INT(x),INT(y)),colour
                y -= 1
                x -= slope
            WEND
        END IF
        
    ELSEIF(x1 < x2) THEN
        
        
        
        WHILE(INT(x) <= x2)
            
            PSET sprite,(INT(x),INT(y)),colour
            x += 1
            y += slope
        WEND
        
    ELSE
        
        WHILE(INT(x) >= x2)
            
            PSET sprite,(INT(x),INT(y)),colour
            x -= 1
            y -= slope
        WEND
    END IF
END SUB


screenres 320,200,32

dim image as any ptr
image = imagecreate(10,10,&h808080)
DrawLine(image,&h125634,1,1,7,7)
put(10,10),image
sleep

Hope it helps, I liked it very much Radical Raccoon, I find it much easier to uinderstand then the "Bresenham" line algorithm.

[Ralph]

axipher:

Is your code in QuickBASIC 4.5? I can't seem to make your
'y += 1 or your 'y -= 1' make any sense in 4.5. Maybe they should be stated as 'y = y + 1' and 'y = y - 1'? Or, maybe, you should cite the progam and version you are using?

[axipher]

Sorry about that, I'm using a new version of HyperBASIC my friend was having me test, it also runs in DOS mode so I figured it should work, I'll fix right now.

[axipher]

Actually, I don't think I can do this for you, I only used QB for about 1 or 2 months and I never erally got into buffers and such in QB, but I tested this code in FreeBASIC and it works perfectly. Maybe someone else can convert it to QB for you, sorry .