Size a Triangle in place.
Blitz3D Forums/Blitz3D Programming/Size a Triangle in place.
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| Hi All, I have a bunch of unwelded triangles scattered across a 2D plane (i.e they all have three verts to themselves and differ in VertexX and VertexY positions, but all are aligned to a Z value of 0. What I wanted to do was to increase their size without moving their orientation or center point. I guess it would involve working out a 2D averaged normal of the two sides connected to a vertex and moving the vertex according to this vector. Any ideas? |
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| I'm sure I saw a function in code archives that did exactly this... |
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| Get each verticy X,Y, and Z values for the triangle: X1# = first verticy X location Y1# = first verticy Y location Z1# = first verticy Z location X2# = second verticy X location Y2# = second verticy Y location Z2# = second verticy Z location X3# = third verticy X location Y3# = third verticy Y location Z3# = third verticy Z location Then average each together: CenterX# = (X1+X2+X3)/3 CenterY# = (Y1+Y2+Y3)/3 CenterZ# = (Z1+Z2+Z3)/3 Then find the tanget space values for these verticies: TanX1# = X1 - CenterX TanY1# = Y1 - CenterY TanZ1# = Z1 - CenterZ TanX2# = X2 - CenterX TanY2# = Y2 - CenterY TanZ2# = Z2 - CenterZ TanX3# = X3 - CenterX TanY3# = Y3 - CenterY TanZ3# = Z3 - CenterZ Then apply your scaleing factor (1 = same size, .5 = half size, 2 = twice the size, etc..) TanX1 = TanX1 * scale TanY1 = TanY1 * scale TanZ1 = TanZ1 * scale TanX2 = TanX2 * scale TanY2 = TanY2 * scale TanZ2 = TanZ2 * scale TanX3 = TanX3 * scale TanY3 = TanY3 * scale TanZ3 = TanZ3 * scale Then apply this to the triangle verticies...you do this by transforming (adding) the scaled tangent space X,Y,Z to the center X,Y,Z...which gives you the location the original verticies should be located at First verticy new X = TanX1 + CenterX First verticy new Y = TanY1 + CenterY First verticy new Z = TanZ1 + CenterZ Second verticy new X = TanX2 + CenterX Second verticy new Y = TanY2 + CenterY Second verticy new Z = TanZ2 + CenterZ Third verticy new X = TanX3 + CenterX Third verticy new Y = TanY3 + CenterY Third verticy new Z = TanZ3 + CenterZ pretty simple... |
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| @ Rob - Can't find it. Some interesting code to find the center of a triangle though. @MSW - I see. Although I only need X and Y as Z is constant. |
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Hey Lee, how about this. Press left and right key to scale.Graphics3D 800,600 SetBuffer BackBuffer() Global camera=CreateCamera() PositionEntity camera,0,0,-10 light=CreateLight() Global mesh=CreateMesh() Global surf=CreateSurface(mesh) v0=AddVertex(surf,0, 1,0) v1=AddVertex(surf,-3,0,0) v2=AddVertex(surf,1, 0,0) tri=AddTriangle(surf,v0,v2,v1) Dim p#(2,2); for scaling the vertexs Global scale#=1.0 While Not KeyHit(1) If KeyDown(203) Then scale=1.01:scale_triangle(surf,0,scale); set scale to either just over 1 or just below 1. If KeyDown(205) Then scale=0.99:scale_triangle(surf,0,scale) UpdateWorld RenderWorld Text 0,0,"scale="+scale Flip Wend End Function scale_triangle(surface,index,t_scale#) For loop=0 To 2; loop through vertexs x and y and store them p(loop,0)=VertexX(surface,index+loop) p(loop,1)=VertexY(surface,index+loop) Next centre_x#= (p(0,0)+p(1,0)+p(2,0))/3; centre calculated by averaging all three points centre_y#= (p(0,1)+p(1,1)+p(2,1))/3; same as above ; multiply the difference between the centerx and the first vertex point x, by t_scale ; then add it the centre point x. same for y For loop=0 To 2 VertexCoords(surface,index+loop,centre_x+t_scale*(p(loop,0)-centre_x),centre_y+t_scale*(p(loop,1)-centre_y),p(loop,2)) Next End Function |
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| Hi Ross C, Yes! Simple and effective. :) Thanks. BTW: You wouldn't believe the ham handed routine I wrote to try and do the same thing! Some days things just don't flow :0 Thanks again :) |
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| Hehe, i know where your coming from :) |
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