Need a little help with the math behind a rasterized line for a tile engine...

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BuccaneerBob

AGK Developer

13

Years of Service

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Joined: 18th Aug 2010

Location: Canada

Posted: 17th Jan 2019 06:55 Edited at: 17th Jan 2019 06:57

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Hey everyone,

Looking for a little help or suggestions/pointers.

I have a tile engine build with App Game Kit, it renders a 400x200 tile map (tiles are 60x60). I did some fancy foot work so that to cut down on battery drain, there's only Screen Width / 60 number of actual tiles on the screen and as you go left/right on the map, it simply updates the "View" to the textures of the offset we're looking at, I'm quite impressed with that, anyway, that's just me bragging. What I'm trying to work out, is rasterized line movement.

The way it works, is based on a tick count (when the tick = 100) if a "Troop" has a Destination X/Y tile that is greater than their current X/Y position, it moves them one step closer to the destination X/Y. The way I build it right now is simply this

+ Code Snippet

 /* if Troop[TroopSlot].MoveToX > tmpX
		NewX = tmpX + 1
	endif
	if Troop[TroopSlot].MoveToX < tmpX
		NewX = tmpX - 1
	endif
	if Troop[TroopSlot].MoveToY > tmpY
		NewY = tmpY + 1
	endif
	if Troop[TroopSlot].MoveToY < tmpY
		NewY = tmpY - 1
	endif */

The problem here is that the troop moves diagonal until the x or y is the same, then they walk in a straight line to the destination tile.

What I'm looking to do is something similar to this:

Here's my entire move function, what I suspect I'd have to do is do the math for the invisible line from Start X, Start Y to End X, End Y, find out where the next tile works out to based on that line and then move the troop the proper direction. However, it's apparent I just stink at math!

+ Code Snippet

function MoveTroop(TroopSlot)

    TileWidth = 60
    TileHeight = 60
    StartX = Troop[TroopSlot].StartX 
    StartY = Troop[TroopSlot].StartY
    CurrentX = Troop[TroopSlot].X
    CurrentY = Troop[TroopSlot].Y 
    EndX = Troop[TroopSlot].MoveToX 
    EndY = Troop[TroopSlot].MoveToY
    

     if Troop[TroopSlot].MoveToX > CurrentX
        NewX = CurrentX + 1
    endif
    if Troop[TroopSlot].MoveToX < CurrentX
        NewX = CurrentX - 1
    endif
    if Troop[TroopSlot].MoveToY > CurrentY
        NewY = CurrentY + 1
    endif
    if Troop[TroopSlot].MoveToY < CurrentY
        NewY = CurrentY - 1
    endif 
    
    
   Troop[TroopSlot].X = NewX
   Troop[TroopSlot].Y = NewY


    
endfunction

Robert Janes (Samu Games)
http://www.samugames.com/artifact

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blink0k

Moderator

11

Years of Service

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Joined: 22nd Feb 2013

Location: the land of oz

Posted: 17th Jan 2019 07:12 Edited at: 17th Jan 2019 07:14

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I think you need to calculate a slope.
First of all you will need to use floats not integers

slope.x = target.x - current.x
slope.y = target.y - current.y

Then you can divide the slope by the number of steps you want to get to your destination.

step.x = slope.x / totalSteps
step.y = slope.y / totalSteps

Then you add the step value to the troop

inc troop.x, step.x
inc troop.y, step.y

Is that what you are after?

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puzzler2018

User Banned

Posted: 17th Jan 2019 07:13

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Hi,

I did a sprite creator with a line feature in there too, here is my algo

// Draw a line
                        if line=1
                            oldx#=getpointerx()
                            oldy#=getpointery()
                            line=2
                        endif
                        if line=2
                             
                            distancex# = getpointerx() - oldx#
                            distancey# = getpointery() - oldy#
                             
                            if abs(distancex#)>=abs(distancey#)
                                stp# = abs(distancex#)
                            else
                                stp# = abs(distancey#)
                            endif
                            distancex# = distancex#/stp#
                            distancey# = distancey#/stp#
                            xx#=oldx#
                            yy#=oldy#
                            col = MakeColor(selectcolorred,selectcolorgreen,selectcolorblue)
                             
                            // clear the tmp color data before we use it
                            for xx=0 to sprites[spritenumber].spritesizex
                                for yy=0 to sprites[spritenumber].spritesizey
                                    tmpcolordata[xx,yy]=0
                                next
                            next
                             
                            for i=1 to stp#
                                 
     
                                    drawBox((xx#),(yy#),((xx#)+size),((yy#)+size),col,col,col,col,1)
                                posx=floor(xx#-originx)/size
                                posy=floor(yy#-originy)/size
                                tmpcolordata[posx,posy]=col
                                inc xx#,distancex#
                                inc yy#,distancey#
                                 
                            next
                             
                        else
 
// Draw a circle

+ Code Snippet

 // Draw a line
                        if line=1
                            oldx#=getpointerx()
                            oldy#=getpointery()
                            line=2
                        endif
                        if line=2
                             
                            distancex# = getpointerx() - oldx#
                            distancey# = getpointery() - oldy#
                             
                            if abs(distancex#)>=abs(distancey#)
                                stp# = abs(distancex#)
                            else
                                stp# = abs(distancey#)
                            endif
                            distancex# = distancex#/stp#
                            distancey# = distancey#/stp#
                            xx#=oldx#
                            yy#=oldy#
                            col = MakeColor(selectcolorred,selectcolorgreen,selectcolorblue)
                             
                            // clear the tmp color data before we use it
                            for xx=0 to sprites[spritenumber].spritesizex
                                for yy=0 to sprites[spritenumber].spritesizey
                                    tmpcolordata[xx,yy]=0
                                next
                            next
                             
                            for i=1 to stp#
                                 
     
                                    drawBox((xx#),(yy#),((xx#)+size),((yy#)+size),col,col,col,col,1)
                                posx=floor(xx#-originx)/size
                                posy=floor(yy#-originy)/size
                                tmpcolordata[posx,posy]=col
                                inc xx#,distancex#
                                inc yy#,distancey#
                                 
                            next
                             
                        else
 
// Draw a circle

Thread to this is

https://forum.thegamecreators.com/thread/223450

Hope this helps for now - others may have better algo's too

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BuccaneerBob

AGK Developer

13

Years of Service

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Joined: 18th Aug 2010

Location: Canada

Posted: 17th Jan 2019 07:15

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You might be onto something there blink0k, though I perhaps am not getting the total steps part or how I'd factor that into it, I'm guessing total steps would be the distance / time to travel from Point A to Point B or something similar to that? The slope part makes total sense, don't know why I didn't think of that!

Robert Janes (Samu Games)
http://www.samugames.com/artifact

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BuccaneerBob

AGK Developer

13

Years of Service

User Offline

Joined: 18th Aug 2010

Location: Canada

Posted: 17th Jan 2019 09:13 Edited at: 17th Jan 2019 09:13

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Got it solved with

+ Code Snippet

	
	StartX = Troop[TroopSlot].X
	StartY = Troop[TroopSlot].Y
	EndX = Troop[TroopSlot].MoveToX
	EndY = Troop[TroopSlot].MoveToY
	dX = EndX - StartX
	dY = EndY - StartY
	if Abs(dX) > Abs(dY)
		Steps = Abs(dX)
	else
		Steps = Abs(dY)
	endif
	XIncrement = dX / steps
	YIncrement = dY / steps
	NewX = Troop[TroopSlot].X + XIncrement
	NewY = Troop[TroopSlot].Y + YIncrement

Robert Janes (Samu Games)
http://www.samugames.com/artifact

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