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## [PyOpenGL-Users] glTranslatef between two glVertex3f

 [PyOpenGL-Users] glTranslatef between two glVertex3f From: Astan Chee - 2009-07-03 02:52:03 ```Hi, I'm trying to draw a line between two points (x0,y0,z0 and x1,y1,z1) like this: glPushMatrix() glEnable(GL_BLEND) glTranslatef(x,y,z) glRotatef(-angle[0],0,1,0) glRotatef(angle[1],1,0,0) glColor4f( 1, 0.0, 0.0, .8 ) glBegin(GL_LINES) glVertex3f(x0,y0,z0) glTranslatef(-x,-y,-z) glRotatef(angle[0],0,1,0) glRotatef(-angle[1],1,0,0) glVertex3f(x1,y1,z1) glEnd() glDisable(GL_BLEND) glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA) glPopMatrix() Where x0,y0,z0 is the point near or in front of the "camera" and the point x1,y1,z1 is the point in "real world coordinates". This doesn't seem to work. How should I be doing this assuming I don't know how to calculate either point in terms of the other? Thanks Astan ```

 [PyOpenGL-Users] glTranslatef between two glVertex3f From: Astan Chee - 2009-07-03 02:52:03 ```Hi, I'm trying to draw a line between two points (x0,y0,z0 and x1,y1,z1) like this: glPushMatrix() glEnable(GL_BLEND) glTranslatef(x,y,z) glRotatef(-angle[0],0,1,0) glRotatef(angle[1],1,0,0) glColor4f( 1, 0.0, 0.0, .8 ) glBegin(GL_LINES) glVertex3f(x0,y0,z0) glTranslatef(-x,-y,-z) glRotatef(angle[0],0,1,0) glRotatef(-angle[1],1,0,0) glVertex3f(x1,y1,z1) glEnd() glDisable(GL_BLEND) glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA) glPopMatrix() Where x0,y0,z0 is the point near or in front of the "camera" and the point x1,y1,z1 is the point in "real world coordinates". This doesn't seem to work. How should I be doing this assuming I don't know how to calculate either point in terms of the other? Thanks Astan ```
 Re: [PyOpenGL-Users] glTranslatef between two glVertex3f From: Ian Mallett - 2009-07-03 03:43:45 Attachments: Message as HTML ```glTranslatef(...) cannot be executed between glBegin(...) and glEnd(). Ian ```
 Re: [PyOpenGL-Users] glTranslatef between two glVertex3f From: Astan Chee - 2009-07-03 04:01:54 Attachments: Message as HTML ```Thanks. I guess my question would then be how do I convert from x,y,z to a,b,c using maths instead of glTranslatef/glRotatef? Cheers Astan Zack Schilling wrote: > You cannot modify the matrix between glBegin and glEnd calls, so no > translation or rotation between plotting of vertices is allowed. > > If I understand what you want, you're trying to draw a line from the > "camera" to an object. Depending on how your frustum is set up, this > may be a bad idea. In any case, it'll look strange and glitchy at > best. But if you insist, here's what you need to do. > > Maintain the position of the camera with (x,y,z) and between loading > the identity and doing any drawing, perform a glTranslatef(-x,-y,-z) > as well as any other "camera" rotations you want. Once that's done, > plot a line from (x,y,z) to (x1,y1,z1), where (x1,y1,z1) are the > coordinates to the object you're drawing the line to. > > glBegin(GL_LINES) > glVertex3f(x,y,z) > glVertex3f(x1,y1,z1) > glEnd() > > You cannot and should not try to adjust the matrix while plotting > points. > > -Zack > > On Jul 2, 2009, at 10:51 PM, Astan Chee wrote: > > >> Hi, >> I'm trying to draw a line between two points (x0,y0,z0 and x1,y1,z1) >> like this: >> >> glPushMatrix() >> >> glEnable(GL_BLEND) >> >> glTranslatef(x,y,z) >> >> glRotatef(-angle[0],0,1,0) >> glRotatef(angle[1],1,0,0) >> >> glColor4f( 1, 0.0, 0.0, .8 ) >> >> glBegin(GL_LINES) >> glVertex3f(x0,y0,z0) >> >> glTranslatef(-x,-y,-z) >> >> glRotatef(angle[0],0,1,0) >> glRotatef(-angle[1],1,0,0) >> >> glVertex3f(x1,y1,z1) >> glEnd() >> >> glDisable(GL_BLEND) >> glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA) >> glPopMatrix() >> >> Where x0,y0,z0 is the point near or in front of the "camera" and the >> point x1,y1,z1 is the point in "real world coordinates". >> This doesn't seem to work. How should I be doing this assuming I don't >> know how to calculate either point in terms of the other? >> Thanks >> Astan >> >> ------------------------------------------------------------------------------ >> _______________________________________________ >> PyOpenGL Homepage >> http://pyopengl.sourceforge.net >> _______________________________________________ >> PyOpenGL-Users mailing list >> PyOpenGL-Users@... >> https://lists.sourceforge.net/lists/listinfo/pyopengl-users >> > > > ```