Rotation issues

**primo** · 24-12-2015, 16:33

some times our graphics rotate in an orbit instead of around itself. also some models do the same thing. there is a sub to adjust the object vertices so it will rotate correctly around itself (the sub is not mine). i will use a model from Petr utility thinEdge (simple house). by default it will rotate around the far end of its front yard, so the house will rotate in orbit, after centering it will rotate around its front door, and wherever we translate it it will still keep the correct rotations
so comment/uncomment line 025 GraphicsCentering() to see the difference.
note: the M15 models have a great and many functions to manipulate its vertices, and i have used some of them to get and then to set the new vertices xyz coordinates.

you need the house model and its textures zipped in the attached file

  Uses "TBGL"
  Uses "UI" 
  Uses "FILE"
  
  DIM hWnd      as dword
  
  ' We will initialize OpenGL and internal buffers
  ' Function also returns window handle
  hWnd = TBGL_CreateWindowEx(" Graphics Centering -  ESC to quit", 640, 480, 32, %TBGL_WS_WINDOWED )      
                                
  TBGL_ShowWindow            ' This will display the window on the screen

  TBGL_GetAsyncKeyState(-1)  ' Reset status of the all keys to prevent immediate quit  
  
  Dim ModelFile As String
  ModelFile = "simple_house.m15"
  TBGL_m15LoadModel ModelFile, "Textures\", 1, 1, 2
  Dim LightX, LightY, LightZ As Single
  LightY = 0 :LightZ = 0
  TBGL_UseLighting 1
  TBGL_UseLightSource %GL_LIGHT0, 1
  TBGL_SetupLightSource %GL_LIGHT0, LightX, LightY, LightZ, 32,32,32,255
   
  '===========================================================
  GraphicsCentering()
  '===========================================================    
    
  while TBGL_IsWindow(hWnd)          ' While window exists, we will draw and check for ESCAPE
    
    tbgl_ClearFrame             ' This clears the frame and prepares it for drawing
        
    TBGL_Camera 0,20,10,0,15,0    ' We will look from point 0,0,10 to 0,0,0 ( origin of coordinates )
   
    TBGL_Translate 0,0,-30 
    TBGL_Rotate GetTickCount/10, 0, 1, 0
        
    TBGL_m15DrawModel 1
    tbgl_DrawFrame              ' This will display the scene
    
    ' When ESCAPE is pressed, we will leave the main loop
    IF TBGL_GetWindowKeyState( hWnd, %VK_ESCAPE ) THEN EXIT while
    
  Wend  
  
  tbgl_DestroyWindow            ' This will destroy the window

 '****************************************** 
 
 Sub GraphicsCentering()
 Local i, vtx As Long
 Local x,y,z As Single
 vtx = TBGL_m15GetModelVertexcount(1)
    
  Dim minx, miny, minz, maxx, maxy, maxz As Single
  Dim corx, cory, corz As Single
  minx =  99999
  miny =  99999
  minz =  99999
  maxx = -99999
  maxy = -99999
  maxz = -99999
  
  For i = 1 To vtx
  'TBGL_m15GetVertexXYZ( ModelID, VertexIndex, varX, varY, varZ )
    TBGL_m15GetVertexXYZ(1, i, x, y, z)
    If x > maxx Then
      maxx = x
    End If
    If x < minx Then
      minx = x
    End If    
    If y > maxy Then
      maxy = y
    End If
    If y < miny Then
      miny = y
    End If   
    If z > maxz Then
      maxz = z
    End If
    If z < minz Then
      minz = z
    End If       
  Next 
  
  corx = (-maxx - minx) /2.0
  cory = (-maxy - miny) /2.0
  corz = (-maxz - minz) /2.0
  
  'MsgBox 0, str$(corx)+"   " + str$(cory)+"    " +str$(corz)
  
  For i = 1 To vtx
  x = TBGL_m15GetVertexX( 1, i )
  y = TBGL_m15GetVertexY( 1, i )
  z = TBGL_m15GetVertexZ( 1, i )

  TBGL_m15SetVertexXYZ(1, i, x+corx, y+cory, z+corz)
             
  Next
  
  End Sub

**Petr Schreiber** · 25-12-2015, 11:09

Hi Primo,

thanks for the nice example. The pivot of rotation is responsibility of the artist (the one who makes the model).
Many times the models are not made centered, to fit a particular scenario (fitting top left corner of grid and such).

So it is not exactly an issue in TBGL itself, but something to be aware of when preparing art for the project.

Few hints for the code:

#1: It is better to specify the normal method via equate. For the case of house the PRECISE gives more pleasing results:

TBGL_m15LoadModel ModelFile, "Textures\", 1, 1, %TBGL_NORMAL_PRECISE

#2: TBGL has dedicated TBGL_ResetKeyState to reset the keys before reading them

Petr

**Petr Schreiber** · 25-12-2015, 11:25

I adjusted the code in a way it uses latest language features - you can see how to center the model without modifying the X, Y, Z of the vertices:
Note: Media files from original code needed

Uses "TBGL"

Function TBMain()
  DWord hWnd = TBGL_CreateWindowEx("Graphics Centering -  ESC to quit", 640, 480, 32, %TBGL_WS_WINDOWED)      
  TBGL_ShowWindow     
  
  String modelFile = "simple_house.m15"
  TBGL_m15LoadModel ModelFile, "Textures\", 1, 1, %TBGL_NORMAL_PRECISE
  
  Dim light As TBGL_TVECTOR3D           
  TBGL_UseLighting TRUE
  TBGL_UseLightSource %GL_LIGHT0, TRUE
  TBGL_SetupLightSource %GL_LIGHT0, light.x, light.y, light.z, 32, 32, 32, 255
  
  Dim center As TBGL_TVECTOR3D
  center = GetModelCenter(1) 
  
  TBGL_ResetKeyState()  
  While TBGL_IsWindow(hWnd)     
    
    TBGL_ClearFrame             
        
      TBGL_Camera 0, 20, 60,
                  0,  0,  0  
      
      TBGL_PushMatrix                                                    
        TBGL_Rotate GetTickCount/10, 0, 1, 0            ' -- Turn model
        TBGL_Translate -center.x, -center.y, -center.z  ' -- Center the rotation
  
        TBGL_m15DrawModel 1
      TBGL_PopMatrix
      
    TBGL_DrawFrame              
    
    If TBGL_GetWindowKeyState( hWnd, %VK_ESCAPE ) Then Exit While
    
  Wend  
  
  TBGL_DestroyWindow
End Function

Function GetModelCenter( modelId As Long ) As String ' -- Hack to return TYPEs

  Long i, vtx
  Single x,y,z
  vtx = TBGL_m15GetModelVertexcount(modelId)
  
  Single minx, miny, minz =  99999   
  Single maxx, maxy, maxz = -99999
  Dim center As TBGL_TVECTOR3D
  
  For i = 1 To vtx
    TBGL_m15GetVertexXYZ(modelId, i, x, y, z)
    maxx = Max(x, maxx)
    minx = Min(x, minx)
    
    maxy = Max(y, maxy)
    miny = Min(y, miny)
  
    maxz = Max(z, maxz)
    minz = Min(z, minz)    
  Next 
  
  center.x = minx + (maxx - minx) / 2.0
  center.y = miny + (maxy - miny) / 2.0
  center.z = minz + (maxz - minz) / 2.0 
  
  Return center

End Function

Petr