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EXAMPLE SOURCE CODE

Lines Intersect

By: Kevin Picone Added: January 7th, 2023

This code is a function that determines if two lines intersect and returns the intersection point as the coordinates (x,y). The function takes in the starting and ending x and y coordinates for each line as arguments. The function first calculates the slope and length of each line. It then uses these values to determine if the lines intersect and, if they do, calculates the intersection point. The function returns a boolean value indicating whether the lines intersect, as well as the x and y coordinates of the intersection point. The function is called in a loop that clears the screen, draws the two lines with the mouse coordinates as one of the endpoints, and prints the intersection point (if the lines intersect).

PlayBasic Code:

Do
// Clear the screen
Cls

// Set line1StartX, line1StartY, line1EndX, and line1EndY to variables
line1StartX=100
line1StartY=100
line1EndX = mousex()
line1EndY = mousey()

// Set line2StartX, line2StartY, line2EndX, and line2EndY to variables
line2StartX=20
line2StartY=200
line2EndX=1000
line2EndY=700

// Draw line1 in black
linec line1StartX, line1StartY, line1EndX, line1EndY,-1

// Draw line2 in green
linec line2StartX, line2StartY, line2EndX, line2EndY,$00ff00

// Check if lines intersect
State,x#,y#=Lines_Intersect(line1StartX, line1StartY, line1EndX, line1EndY,_
            line2StartX, line2StartY, line2EndX, line2EndY)

// Print intersect state
print State

// If lines intersect, draw a red circle at intersect point
if State
	Circlec X#,y#,10,true,$ff0000
endif

// Display the screen

sync
loop spacekey()

	end


 
Function Lines_Intersect(line1StartX, line1StartY, line1EndX, line1EndY, line2StartX, line2StartY, line2EndX, line2EndY)

// Initialize variables
intersects = False
intersectX = 0
intersectY = 0
s1_x# = line1EndX - line1StartX
s1_y# = line1EndY - line1StartY
s2_x# = line2EndX - line2StartX
s2_y# = line2EndY - line2StartY

// Calculate s and t
s# = (-s1_y# * (line1StartX - line2StartX) + s1_x# * (line1StartY - line2StartY)) / (-s2_x# * s1_y# + s1_x# * s2_y#)
t# = ( s2_x# * (line1StartY - line2StartY) - s2_y# * (line1StartX - line2StartX)) / (-s2_x# * s1_y# + s1_x# * s2_y#)

// Check if s and t are within valid range
if s# >= 0 and s# <= 1 and t# >= 0 and t# <= 1
	// Set intersects to true and calculate intersectX and intersectY
    intersects = True
    intersectX# = line1StartX + (t# * s1_x#)
    intersectY# = line1StartY + (t# * s1_y#)
EndIf

// Return intersects, intersectX, and intersectY

EndFunction intersects, intersectX#, intersectY#

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