2D dot line collision - GameCreators Forum

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Wiley85

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Posted: 7th Feb 2009 16:39

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Hello everybloody! I've a new problem concerning basic 2d drawing collisions. Specifically, I've a program that launches a dot line on a projectile path dependant on user input. I want the program to be able to detect when the dot line has collided with any of the lines I've use to create a basic terrain. ANy suggestions?

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Phaelax

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Posted: 7th Feb 2009 18:21

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So you're drawing the projectile's path using a dotted line?

You can loop through all the line segments which make up your terrain and check to see if a dot is below that line or not.

There is an equation for detecting that, but I don't know it off hand. I have it written down at home, but won't be there until tomorrow.

Your signature has been erased by a mod because it's larger than 600x120

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Ashingda 27

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Posted: 7th Feb 2009 19:52

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Have you tried using the point(x,y) function? It returns a color on the screen.

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BN2 Productions

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Posted: 8th Feb 2009 07:17

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y=mx+b (or for simplicity y-y1=m(x-x1))

so:

ya=m1(x-x1)+y1
yb=m2(x-x2)+y2

but ya and yb will be the same where they intersect so

m1(x-x1)+y1=m2(x-x2)+y2

m1x-m1x1+y1=m2x-m2x2+y2
m1x-m2x=m1x1-m2x2-y1+y2

x=(m1x1-m2x2-y1+y2)/(m1-m2)
then

y=m1(x-x1)+y1

Key:
m1=slope of line 1
m2=slope of line 2
(x1,y1)=a point on line 1
(x2,y2)=a point on line 2

(x,y)=the point of intersection.

Great Quote:
"Time...LINE??? Time isn't made out of lines...it is made out of circles. That is why clocks are round!" -Caboose

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Wiley85

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Posted: 9th Feb 2009 03:18

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Ok, it's a mess, but here's what I've come up with so far. I couldn't figure out how to implement any of those formulas though. Check it out!

`STARTING BOX, FIELD, TURRETS, AND STARTING VARIABLES
HIDE MOUSE
INK RGB(0,255,0),RGB(0,0,0)
LINE 0,0,639,0 : LINE 0,0,0,470 : LINE 0,470,639,470 : LINE 639,470,639,0

LINE 0,375,640,375

CIRCLE 20,375,5
CIRCLE 615,375,5

G#=9.8
1S=0
2S=0

`***********INPUT PLAYER 1 INFO***********
1:

INK RGB(255,255,255),RGB(0,0,0)
SET CURSOR 10,425
INPUT "VELOCITY> ",1V#

SET CURSOR 10,440
INPUT "ANGLE> ",1ANG#

INK RGB(0,0,0),RGB(0,0,0)
BOX 10,425,115,455

1XI=20
1YI=375
T#=0
Y=0

`DRAW LINE FOR PLAYER 1 PROJECTILE
REPEAT

INK RGB(255,255,255),RGB(255,255,255)

1X#=(1V#*COS(1ANG#))*T#
1Y#=(G#*T#)-(1V#*SIN(1ANG#)*Y)

1X#=1X#/10
	1Y#=1Y#/10

1X=1XI+1X#
		1Y=1YI+1Y#

DOT 1X,1Y
INK RGB(0,0,0),RGB(0,0,0)
DOT 1X,1Y

1YI=1YI+1Y#

Y=1

T#=T#+0.25

IF 1X<620 AND 1X>610 AND 1Y<380 AND 1Y>370 THEN 1S=1S+1

UNTIL 1Y>375 OR 1X>640

BOX 10,390,75,405
	INK RGB(255,255,255),RGB(0,0,0)
	SET CURSOR 10,390
	PRINT "SCORE> ";1S

`***********INPUT PLAYER 2 INFO***********

INK RGB(255,255,255),RGB(0,0,0)
SET CURSOR 525,425
INPUT "VELOCITY> ",2V#
SET CURSOR 525,440
INPUT "ANGLE> ",2ANG#
INK RGB(0,0,0),RGB(0,0,0)
BOX 500,425,630,455

2XI=615
2YI=375
T#=0
Y=0

`DRAW LINE FOR PLAYER 2 PROJECTILE
REPEAT
INK RGB(255,255,255),RGB(255,255,255)

2X#=(2V#*COS(2ANG#))*T#
2Y#=(G#*T#)-(2V#*SIN(2ANG#)*Y)

2X#=2X#/10
	2Y#=2Y#/10

2X=2XI-2X#
		2Y=2YI+2Y#

DOT 2X,2Y
INK RGB(0,0,0),RGB(0,0,0)
DOT 2X,2Y

2YI=2YI+2Y#

Y=1

T#=T#+0.25

IF 2X<25 AND 2X>15 AND 2Y<380 AND 2Y>370 THEN 2S=2S+1

UNTIL 2Y>375 OR 2X<0

BOX 500,390,600,405
	INK RGB(255,255,255),RGB(0,0,0)
	SET CURSOR 525,390
	PRINT "SCORE> ";2S

IF 2S+1S=5 AND G#=9.8 THEN GOSUB CG1
IF 2S+1S=7 AND G#<10 THEN GOSUB CG2

GOTO 1

`FIRST GRAVITY CHANGE
CG1:

G#=4.9

SET CURSOR 200,50
	PRINT "GRAVITY HAS BEEN REDUCED!"
	SLEEP 3000
	INK RGB(0,0,0),RGB(0,0,0)
	BOX 200,50,500,75

RETURN

`SECOND GRAVITY CHANGE
CG2:

G#=G#+2

SET CURSOR 200,50
	PRINT "GRAVITY HAS BEEN INCREASED!"
	SLEEP 3000
	INK RGB(0,0,0),RGB(0,0,0)
	BOX 200,50,500,75

RETURN

+ Code Snippet

`STARTING BOX, FIELD, TURRETS, AND STARTING VARIABLES
HIDE MOUSE
INK RGB(0,255,0),RGB(0,0,0)
LINE 0,0,639,0 : LINE 0,0,0,470 : LINE 0,470,639,470 : LINE 639,470,639,0

LINE 0,375,640,375

CIRCLE 20,375,5
CIRCLE 615,375,5

G#=9.8
1S=0
2S=0

`***********INPUT PLAYER 1 INFO***********
1:

INK RGB(255,255,255),RGB(0,0,0)
SET CURSOR 10,425
INPUT "VELOCITY> ",1V#

SET CURSOR 10,440
INPUT "ANGLE> ",1ANG#

INK RGB(0,0,0),RGB(0,0,0)
BOX 10,425,115,455

1XI=20
1YI=375
T#=0
Y=0

`DRAW LINE FOR PLAYER 1 PROJECTILE
REPEAT

INK RGB(255,255,255),RGB(255,255,255)

1X#=(1V#*COS(1ANG#))*T#
1Y#=(G#*T#)-(1V#*SIN(1ANG#)*Y)

	1X#=1X#/10
	1Y#=1Y#/10

		1X=1XI+1X#
		1Y=1YI+1Y#

DOT 1X,1Y
INK RGB(0,0,0),RGB(0,0,0)
DOT 1X,1Y

	1YI=1YI+1Y#

	Y=1

	T#=T#+0.25

IF 1X<620 AND 1X>610 AND 1Y<380 AND 1Y>370 THEN 1S=1S+1

UNTIL 1Y>375 OR 1X>640

BOX 10,390,75,405
	INK RGB(255,255,255),RGB(0,0,0)
	SET CURSOR 10,390
	PRINT "SCORE> ";1S

`***********INPUT PLAYER 2 INFO***********

INK RGB(255,255,255),RGB(0,0,0)
SET CURSOR 525,425
INPUT "VELOCITY> ",2V#
SET CURSOR 525,440
INPUT "ANGLE> ",2ANG#
INK RGB(0,0,0),RGB(0,0,0)
BOX 500,425,630,455

2XI=615
2YI=375
T#=0
Y=0

`DRAW LINE FOR PLAYER 2 PROJECTILE
REPEAT
INK RGB(255,255,255),RGB(255,255,255)

2X#=(2V#*COS(2ANG#))*T#
2Y#=(G#*T#)-(2V#*SIN(2ANG#)*Y)

	2X#=2X#/10
	2Y#=2Y#/10

		2X=2XI-2X#
		2Y=2YI+2Y#

DOT 2X,2Y
INK RGB(0,0,0),RGB(0,0,0)
DOT 2X,2Y

	2YI=2YI+2Y#

	Y=1

	T#=T#+0.25

IF 2X<25 AND 2X>15 AND 2Y<380 AND 2Y>370 THEN 2S=2S+1

UNTIL 2Y>375 OR 2X<0

BOX 500,390,600,405
	INK RGB(255,255,255),RGB(0,0,0)
	SET CURSOR 525,390
	PRINT "SCORE> ";2S

IF 2S+1S=5 AND G#=9.8 THEN GOSUB CG1
IF 2S+1S=7 AND G#<10 THEN GOSUB CG2

GOTO 1

`FIRST GRAVITY CHANGE
CG1:

G#=4.9

SET CURSOR 200,50
	PRINT "GRAVITY HAS BEEN REDUCED!"
	SLEEP 3000
	INK RGB(0,0,0),RGB(0,0,0)
	BOX 200,50,500,75

RETURN

`SECOND GRAVITY CHANGE
CG2:

G#=G#+2

SET CURSOR 200,50
	PRINT "GRAVITY HAS BEEN INCREASED!"
	SLEEP 3000
	INK RGB(0,0,0),RGB(0,0,0)
	BOX 200,50,500,75

RETURN

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BN2 Productions

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Posted: 9th Feb 2009 04:17

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Here is a physics formula that you can use to calculate a projectile's path:

S=.5*GRAVITY*TIME^2+VELOCITY INITIAL*sin(ANGLE)*TIME+S ORIGINAL

Or, in a more friendly form:

Y=.5*G*(X-X Initial)^2+Vi*sin(ANGLE)*(X-X Initial)+Y Initial

Where X Initial and Y Initial are the starting points (the player locations).

LONG NOTE: The Velocity is multiplied by the Sine of the angle because of this:

The velocity is the speed along the line of action (the angled line). However, you need the x and y components of that velocity to do anything with it (since all other measurements are taken in x and y parts). So, using a bit of trig (if you don't know anything about trig, you can read on if you want, or you can just accept the fact), we can see that the y component is the hypotenuse of a triangle multiplied by the sine of the angle (remember, Sin(angle)=opposite/hypotenuse therefore hypotenuse*sin(angle)=opposite). Here is a diagram to help illustrate.

So, the opposite side from the angle of 30 degrees is the red side. Therefore, according to the formula, Red=black*sin(30), or Red=10*sin(30). Using a calculator we can find that sin(30)=.5, thereofre RED=10*.5 thus RED=5.
[/LONG NOTE]

Get it?

Great Quote:
"Time...LINE??? Time isn't made out of lines...it is made out of circles. That is why clocks are round!" -Caboose

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Wiley85

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Posted: 9th Feb 2009 15:17

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I do. That sounds much less messy than what I've done. I have taken a trig class and that's how I came up with my formulas. It looks like your formula would just find the y position, so for x I just use the same formula with cosine instead and without gravity correct?

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BN2 Productions

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Posted: 10th Feb 2009 08:25

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With x you just treat it like time, so that you can increase it by a fixed amount.

Alternatively, you can use

S=V*cos(angle)*Time+S INIT

But that would require you to time the shots. It is easier just to use the difference in x positions as the time and increment the x position by a fixed amount.

Great Quote:
"Time...LINE??? Time isn't made out of lines...it is made out of circles. That is why clocks are round!" -Caboose

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