Finding 3Dworld position of texture pixel (texel)?

Blitz3D Forums/Blitz3D Programming/Finding 3Dworld position of texture pixel (texel)?

Beaker (Posted 2006) [#1]

I can probably work this out, but has anyone already created a function to calculate the 3D world position of a texture pixel on a particular triangle/surface? Any help would be appreciated. Thanks.

Mustang (Posted 2006) [#2]

This should do it, more or less: http://www.blitzbasic.com/codearcs/codearcs.php?code=515 [edit] Ooops, or maybe not... if I understud the question correctly after second reading.

Baystep Productions (Posted 2006) [#3]

As in a radar map? I did it as a 2D image for the hud... And I as I remember it's easy math, just get the pixel cordinate x&y subtract half the width&height (if you want the center to be 0) devide it by the whole width& height and multiply the result by the scale of the map. So it would be something like... x#=(Pixel_X-(ImageWidth(map)/2))/ImageWidth(map) z#=(Pixel_Y-(ImageHeight(map)/2))/ImageHeight(map) PositionEntity(obj,x#*Scale#,0,z#=*Scale#)

Bobysait (Posted 2006) [#4]

use LinePick (or CameraPick ) - Surf=pickedsurface() - Tri=PickedTriangle() - get the 3 vertices of the triangle : V0=Trianglevertex(surf,0) V1=Trianglevertex(surf,1) V2=Trianglevertex(surf,2) VU0#=vertexU(surf,V0) VV0#=vertexV(surf,V0) VU1#=vertexU(surf,V1) VV1#=vertexV(surf,V1) VU2#=vertexU(surf,V2) VV2#=vertexV(surf,V2) => And get the coord : U#=(VU0+VU1+VU2)/3 V#=(VV0+VV1+VV2)/3 Then convert the UV with texturecoord using: => GetSurfaceBrush => getBrushTexture() And finally => texturewidth() , TextureHeight() => Pixel_I=U*TextureWidth() => Pixel_J=V*TextureHeight()

Jeppe Nielsen (Posted 2006) [#5]

This will do what you want, I think :-) Kind of the reverse of the code Mustang showed. Look at the TFormTexel function: ;this will calculate the world coordinates of a texel, at the texture pixel coordinates specified ;results are grabbed with TFormedX(),TFormedY() and TFormedZ() TFormTexel(mesh,texture,pixelx,pixely) ;Texel to world coordinates, use the TFormTexel function. Graphics3D 800,600,32,2 HidePointer camera=CreateCamera() PositionEntity camera,3,4,-4 RotateEntity camera,50,0,0 CameraClsColor camera,0,0,255 tex=CreateTexture(512,512) quad=CreateMesh() surface=CreateSurface(quad) AddVertex surface,0,0,0,0,0 AddVertex surface,2,0,0,1,0 AddVertex surface,2,0,-2,1,1 AddVertex surface,0,0,-4,0,1 AddTriangle surface,0,1,3 AddTriangle surface,1,2,3 EntityFX quad,1 sphere=CreateSphere(32) PositionEntity sphere,3,0,0 EntityFX sphere,1 cube=CreateCube() PositionEntity cube,6,0,0 EntityFX cube,1 EntityTexture quad,tex EntityTexture sphere,tex EntityTexture cube,tex Local marker[2] For n=0 To 2 marker[n]=CreateCube() ScaleEntity marker[n],0.15,0.15,0.15 EntityAlpha marker[n],0.8 EntityFX marker[n],1 Next Repeat mx=MouseX() my=MouseY() DrawToTexture(tex,mx,my) If TFormTexel(quad,tex,mx,my)=True PositionEntity marker[0],TFormedX(),TFormedY(),TFormedZ() Else PositionEntity marker[0],10000,10000,10000 EndIf If TFormTexel(sphere,tex,mx,my)=True PositionEntity marker[1],TFormedX(),TFormedY(),TFormedZ() Else PositionEntity marker[1],10000,10000,10000 EndIf If TFormTexel(cube,tex,mx,my)=True PositionEntity marker[2],TFormedX(),TFormedY(),TFormedZ() Else PositionEntity marker[2],10000,10000,10000 EndIf RenderWorld() Plot mx,my Rect 0,0,TextureWidth(tex),TextureHeight(tex),False Color 255,255,255 Oval mx-4/2,my-4/2,4,4,True Oval mx-40,my-40,80,80,False Flip Until KeyDown(1) End ;this will calculate the world coordinates of a texel, at the texture pixel coordinates specified ;results are grabbed with TFormedX(),TFormedY() and TFormedZ() Function TFormTexel(mesh,texture,pixelx,pixely) twid=TextureWidth(texture)-1 thei=TextureHeight(texture)-1 px#=Float(pixelx)/twid py#=Float(pixely)/thei surfs=CountSurfaces(mesh) For surf=1 To surfs surface=GetSurface(mesh,surf) tris=CountTriangles(surface)-1 For triangle=0 To tris vert0=TriangleVertex(surface,triangle,0) vert1=TriangleVertex(surface,triangle,1) vert2=TriangleVertex(surface,triangle,2) x0#=VertexU(surface,vert0) y0#=VertexV(surface,vert0) x1#=VertexU(surface,vert1) y1#=VertexV(surface,vert1) x2#=VertexU(surface,vert2) y2#=VertexV(surface,vert2) ;check if the point is in the texture triangle If IsInTriangle( px#,py#, x0#,y0#,x1#,y1#,x2#,y2# ) ;equations taken from here: ; ;http://local.wasp.uwa.edu.au/~pbourke/geometry/lineline2d/ ; ua#=( (x2-x1)*(y0-y1)-(y2-y1)*(x0-x1) ) / ( (y2-y1)*(px-x0)-(x2-x1)*(py-y0) ) ex#=x0+ua*(px-x0) ey#=y0+ua*(py-y0) dx#=ex-x1 dy#=ey-y1 le#=Sqr(dx*dx+dy*dy) dx#=x2-x1 dy#=y2-y1 d1#=le#/Sqr(dx*dx+dy*dy) ua#=( (x2-x0)*(y1-y0)-(y2-y0)*(x1-x0) ) / ( (y2-y0)*(px-x1)-(x2-x0)*(py-y1) ) ex#=x1+ua*(px-x1) ey#=y1+ua*(py-y1) dx#=ex-x0 dy#=ey-y0 le#=Sqr(dx*dx+dy*dy) dx#=x2-x0 dy#=y2-y0 d2#=le#/Sqr(dx*dx+dy*dy) px1#=VertexX(surface,vert0) py1#=VertexY(surface,vert0) pz1#=VertexZ(surface,vert0) px3#=VertexX(surface,vert1) py3#=VertexY(surface,vert1) pz3#=VertexZ(surface,vert1) dx#=VertexX(surface,vert2)-VertexX(surface,vert1) dy#=VertexY(surface,vert2)-VertexY(surface,vert1) dz#=VertexZ(surface,vert2)-VertexZ(surface,vert1) px2#=px3+dx*d1# py2#=py3+dy*d1# pz2#=pz3+dz*d1# dx#=VertexX(surface,vert2)-VertexX(surface,vert0) dy#=VertexY(surface,vert2)-VertexY(surface,vert0) dz#=VertexZ(surface,vert2)-VertexZ(surface,vert0) px4#=px1+dx*d2# py4#=py1+dy*d2# pz4#=pz1+dz*d2# ;equations taken from here: ; ;http://mathworld.wolfram.com/Line-LineIntersection.html ; ax#=px2#-px1# ay#=py2#-py1# az#=pz2#-pz1# bx#=px4#-px3# by#=py4#-py3# bz#=pz4#-pz3# cx#=px3#-px1# cy#=py3#-py1# cz#=pz3#-pz1# qx1# = cy * bz - by * cz qy1# = cz * bx - bz * cx qz1# = cx * by - bx * cy qx2# = ay * bz - by * az qy2# = az * bx - bz * ax qz2# = ax * by - bx * ay dot#=qx1*qx2+qy1*qy2+qz1*qz2 le#=Sqr(qx2*qx2+qy2*qy2+qz2*qz2) si#=dot#/(le#*le#) pointx#=px1#+ax#*si# pointy#=py1#+ay#*si# pointz#=pz1#+az#*si# TFormPoint pointx,pointy,pointz,mesh,0 Return True EndIf Next Next End Function ;taken from the blitzbasic site: ; ;http://www.blitzbasic.co.nz/codearcs/codearcs.php?code=483 ; Function IsInTriangle( px#,py#, ax#,ay#,bx#,by#,cx#,cy# ) Local bc#,ca#,ab#,ap#,bp#,cp#,abc# bc# = bx*cy - by*cx ca# = cx*ay - cy*ax ab# = ax*by - ay*bx ap# = ax*py - ay*px bp# = bx*py - by*px cp# = cx*py - cy*px abc# = Sgn(bc + ca + ab) Return (abc*(bc-bp+cp)>0) And (abc*(ca-cp+ap)>0) And (abc*(ab-ap+bp)>0) End Function Function DrawToTexture(tex,mx,my,size=4) SetBuffer TextureBuffer(tex) Cls Color 255,255,255 Oval mx-size/2,my-size/2,size,size,True Oval mx-40,my-40,80,80,False SetBuffer BackBuffer() End Function

Bobysait (Posted 2006) [#6]

good work. But maybe parsing all triangles of the mesh to get one coord could be long . Maybe using a preloading system to store triangles datas should get it work faster no ? But it should also use bigs array ...

Beaker (Posted 2006) [#7]

Thanks guys, particularly Jeppe. Just what I needed.

RemiD (Posted 2016) [#8]

Thanks Jeppe, very useful code !