selection : hits not recorded

OpenGL OpenGL: Basic Coding
1

im having this really wierd problem where my hits are show in the selection buffer at times and at times they dont show. i still havent come across the pattern when this happens, but this is unusual.

shtHits = 0
glGetIntegerv glgViewport, viewport(0)
glSelectBuffer shtBUFSIZE, intSelectbuffer(0)
glRenderMode (GL_SELECT)

glInitNames
glPushName 0 'intializing the name stack

'setting the same geomety as for normal view
glMatrixMode (GL_PROJECTION)
glPushMatrix 'saving the original matrix

    glLoadIdentity

    gluPickMatrix dblX, viewport(3) - dblY, dblXDist, dblYDist, viewport(0)

    'set Camera view, the same for picking as for viewing
    gluPerspective msngFieldOfView, msngAspectRatio, mdblNearField, mdblFarField
    
    glMatrixMode (GL_MODELVIEW)

    glPushMatrix

my translations and rotations
draw all shapes
…

    glPopMatrix
    glFlush
    shtHits = glRenderMode(GL_RENDER)   'hits = objects in hit
   
    glPopMatrix 'restoring the original matrix
    
    If shtHits > 0 Then

        lngNameNum = 0
        dblDist = 4294967295#

        For intI = 0 To shtHits - 1

                'find nearest
                If (intSelectbuffer((intI) * 4 + 1) < dblDist) Then
                    dblDist = intSelectbuffer((intI) * 4 + 1)
                    lngNameNum = intSelectbuffer((intI) * 4 + 3)
                End If

        Next intI
    
    End If

instead of renderin the whole scene everytime, i have a screen shot thatz rendered in a 2d othro mode. will that make any difference on selection. i think it wont cause the values in the selection buffer are generated when the same DLs are called when rendering mode is GL_SELECT.

[This message has been edited by mithun_daa (edited 02-10-2004).]

2

Hi !

As long as you make sure you do render the full scene when you are in selection mode it should not cause any problem.

3

Originally posted by mikael_aronsson:
[b]Hi !

As long as you make sure you do render the full scene when you are in selection mode it should not cause any problem.

[/b]

do i need to render the full scene in selection mode or do i render only the stuff that has names loaded onto the name stack? cause i have some part of the scene like the terrain that i dont want selected and the objects on the terrain are the ones that can be selected. currently im renderin only the objects in the selection mode.

also, i observed that usually, only the first time i select an object after i zoom in or out, there is a hit record and there are some values in the selection buffer. orelse the selection buffer is either filled with 0s or only the first 3 fields are filled and the the 4th field which contains the DL # is 0

it also gives different names for the same object at different times
[This message has been edited by mithun_daa (edited 02-11-2004).]

[This message has been edited by mithun_daa (edited 02-11-2004).]

4

Hi !

No you should not render stuff that should not be part of the hittest, if you do you can get some wacky hit records.

Mikael