Filled Triangle

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Pakz	Created : 06 July 2017 System : Browser Based Language : Monkey-X Filled Triangle Fill triangles using bresenham algorithm Flash applet with the triangle fill routine.
' ' Fill triangles using the bresenham algorithm ' Import mojo Class filledtriangle ' These variables are the points of ' the triangle. Field x1:Int,y1:Int Field x2:Int,y2:Int Field x3:Int,y3:Int ' This variable is the y of the triangle ' that has the lowest value. Field lowesty:Int ' This is the total height of the triangle. Field sizey:Int ' These arrays hold the x coordinates with ' which we draw the lines. Field lefty:Int[] Field righty:Int[] ' Here we create and draw the triangle. Method New(x1:Int,y1:int,x2:Int,y2:int,x3:int,y3:int) ' In order to draw below ZERO we add a value to the inputted ' coordinates. We decrease this amount when drawing the ' actual triangles on the canvas. Local offscreen:Int=10000 x1 += offscreen y1 += offscreen x2 += offscreen y2 += offscreen x3 += offscreen y3 += offscreen ' We need to know which coordinate has the lowest ' y value and we put that in the lowesty variable. 'find lowest If y1<y2 And y1<y3 Then lowesty = y1 If y2<y1 And y2<y3 Then lowesty = y2 If y3<y1 And y3<y2 Then lowesty = y3 ' We also need to know the total height of the ' triangle so we can create a array of that size ' where we store the left and right side line ' coordinates in. 'find height If y1>y2 And y1>y3 Then sizey = y1-lowesty If y2>y1 And y2>y3 Then sizey = y2-lowesty If y3>y1 And y3>y2 Then sizey = y3-lowesty ' ' If there is nothing to draw then ' exit this method. If sizey = 0 Then Return ' Create two arrays which will hold the coordinates ' for the lines inside the triangles. The x coordinates. lefty = New Int[sizey+1] righty = New Int[sizey+1] ' Here we fill the lefty and righty arrays with the ' x coordinates of the lines inside the triangles. bline(x1,y1,x2,y2) bline(x2,y2,x3,y3) bline(x1,y1,x3,y3) ' Here we draw the lines inside the triangles. Filling ' it. You can do per pixel for colloring ect. For Local y:Int=0 until sizey DrawLine(lefty[y]-offscreen,lowesty+y-offscreen,righty[y]-offscreen,lowesty+y-offscreen) Next End Method ' ' This is the bresenham algorithm. It is modified so ' it fills two arrays with the x coordinates of the ' lines inside the triangles. Method bline:Void(x4:Int,y4:Int,x5:Int,y5:Int) Local dx:Int, dy:Int, sx:Int, sy:Int, e:Int dx = Abs(x5 - x4) sx = -1 If x4 < x5 Then sx = 1 dy = Abs(y5 - y4) sy = -1 If y4 < y5 Then sy = 1 If dx < dy Then e = dx / 2 Else e = dy / 2 End If Local exitloop:Bool=False While exitloop = False ' Here we fill the left and right sides arrays. ' we draw lines between these later on to fill the triangle If lefty[y4-lowesty] = 0 Then 'If left not used then fill left lefty[y4-lowesty] = x4 Elseif righty[y4-lowesty] = 0 'if right not used then fill right righty[y4-lowesty] = x4 Else 'if both sides are filled If lefty[y4-lowesty] = x4 Then 'overwrite same value lefty[y4-lowesty] = x4 Else 'write new value righty[y4-lowesty] = x4 End If End If If x4 = x5 If y4 = y5 exitloop = True End If End If If dx > dy Then x4 += sx ; e -= dy If e < 0 Then e += dx ; y4 += sy Else y4 += sy ; e -= dx If e < 0 Then e += dy ; x4 += sx Endif Wend End Method End Class Class MyGame Extends App ' cnt is used for the seed Field cnt:Int ' mytriangle is used to draw a triangle Field mytriangle:filledtriangle Method OnCreate() SetUpdateRate(10) End Method Method OnUpdate() ' If pressed space/touch/lmb then new set of triangles If KeyHit(KEY_SPACE) Or MouseHit(MOUSE_LEFT) Then cnt+=1 End Method Method OnRender() Cls 0,0,0 ' Always draw the same using this seed Seed = cnt ' Draw 100 triangles For Local i:=0 Until 100 Local x1:Int=Rnd(0,DeviceWidth) Local y1:Int=Rnd(0,DeviceHeight) Local x2:Int=x1+Rnd(-80,80) Local y2:Int=y1+Rnd(-80,80) Local x3:Int=x1+Rnd(-80,80) Local y3:Int=y1+Rnd(-80,80) SetColor(Rnd(255),Rnd(255),Rnd(255)) mytriangle = New filledtriangle(x1,y1,x2,y2,x3,y3) Next ' Draw some text SetColor 255,255,255 DrawText('Press the space bar/lmb/touch to draw new set.',0,0) End Method End Class Function Main() New MyGame() End Function --v
Latest Update I was reading on the javagaming forum and noticed someone describing how you could fill triangles by filling it with lines. Basically you use the bresenham line algorithm and with every step there you store the x coordinates at either the left or right side. When they are stored you then loop through the array where they are stored and use these x coordinates with the drawline command. I spend a while thinking on how I would do this and I was able to rather quickly make it work in monkey.

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Filled Triangle

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