First pixel

[Peter]

Deleted...

[kryton9]

Peter, I am not sure if this is what you are looking for, but if you do no translations and just put vertices on the screen first-- then the center of the screen is 0,0.  The lower left of the screen is -1,-1.  The top right is 1, 1.

Here is more info about pixels at this site: http://www.opengl.org/sdk/docs/man/xhtml/glReadPixels.xml

[Charles Pegge]

Hi Peter,

In terms of texture:

lower left 0,0 : top right 1,1

This means the y coordinate is the opposite to that of a Windows surface.

In terms of 3d geometry:

centre of viewport surface: 0,0,0
lower left -x,-y
upper right+x,+y
toward viewer =+z
away from viewer =-z

Any point of a texture can be mapped to any point on a 2d/3d surface, so you can do inverted and mirror image textures at any scale. The pixels are interpolated so you don't see pixelation when the texture is close up or enlarged.


Charles

[Charles Pegge]

Hi Peter.

I'm still not clear about the meaning of your question. Opengl does not directly deal with pixels, except when creating new textures. And all textures have to be bound to a geometric surface.

Perhaps GUI/openglWin2.o2bas will help:

The is the Scene rendering part: You can play with the texture coords and see what happens.

Code: OxygenBasic

1.  
2.   '-----------------------------------
3.  'CREATE SCENE FRAME AND SWAP BUFFERS
4.  '===================================
5.  '
6.  static RECT crect
7.   static single sx,sy,sz
8.   '
9.  if act then
10.   '----------
11.  '
12.  '
13.  'SET THE VIEWPORT AND PERSPECTIVE
14.  '
15.  GetClientRect  hwnd,&cRect
16.   glViewport 0, 0, crect.right, crect.bottom
17.   double aspect=crect.right/crect.bottom
18.   '
19.  glMatrixMode   GL_PROJECTION
20.   glLoadIdentity
21.   gluPerspective 45, aspect, 1.0, 100
22.   glMatrixMode   GL_MODELVIEW
23.   glLoadIdentity
24.   '
25.  glClear GL_COLOR_BUFFER_BIT or GL_DEPTH_BUFFER_BIT
26.   glClearColor 0.5, 0, 0, 0
27.   '
28.  'ACTIVATE TEXTURE
29.  '----------------
30.  '
31.  glEnable GL_TEXTURE_2D
32.   glBindTexture GL_TEXTURE_2D,texn[1]
33.   '
34.  sx=0.2 : sy=0.16 : sz=-1
35.   '
36.  '
37.  'MOVEMENT
38.  '--------
39.  '
40.  'glrotatef ang1, 0,0,1
41.  single x=cos(rad(ang1))*.1 ,y=sin(rad(ang1))*.1,z=0
42.   gltranslatef x,y,z
43.   '
44.  'DRAW SHAPE
45.  '----------
46.  '
47.  'this quad is drawn clockwise
48.  '
49.  glbegin GL_QUADS
50.   '
51.  glTexCoord2f 0,0 : glvertex3f -sx, -sy,  sZ
52.   glTexCoord2f 0,1 : glvertex3f -sx,  sy,  sZ
53.   glTexCoord2f 1,1 : glvertex3f  sx,  sy,  sZ
54.   glTexCoord2f 1,0 : glvertex3f  sx, -sy,  sZ
55.   '
56.  glend
57.   '
58.  glDisable GL_TEXTURE_2D
59.   '
60.  glfinish
61.   swapBuffers hdc
62.   '
63.  '
64.  'UPDATE ROTATION ANGLES
65.  '----------------------
66.  '
67.  ang1+=angi1
68.   act=0
69.   '
70.  return 0 'done
71.  

Charles

[Charles Pegge]

Peter.

This will run from examples/gui

Texture Generation

Code: OxygenBasic

1.  
2.   'Prepare Textures
3.  '----------------
4.  '
5.  glGenTextures 2, texn
6.   '
7.  sys res=512
8.   sys pixels[4096], tx=64, ty=64, x, y, p, c
9.   '
10.  for y=1 to 64
11.     for x=1 to 64
12.       if x<33 and y<33
13.         c=0xff00ff00       'GREEN BOTTOM LEFT
14.      elseif x>32 and y>32
15.         c=0xffff0000       'BLUE TOP RIGHT
16.      else
17.         c=0xff0000ff       'RED
18.      end if
19.       p=y*64-64+x
20.       pixels[p]=c
21.     next
22.   next
23.   '
24.  'GL_NEAREST
25.  'GL_LINEAR
26.  glBindTexture GL_TEXTURE_2D, texn[1]
27.   glTexParameteri GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR
28.   '
29.  'GL_NEAREST
30.  'GL_LINEAR
31.  'GL_NEAREST_MIPMAP_NEAREST         0x2700
32.  'GL_LINEAR_MIPMAP_NEAREST          0x2701
33.  'GL_NEAREST_MIPMAP_LINEAR          0x2702
34.  'GL_LINEAR_MIPMAP_LINEAR           0x2703
35.  '
36.  glTexParameteri GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR
37.   glTexImage2D GL_TEXTURE_2D, 0, 4, tx, ty, 0, GL_RGBA, GL_UNSIGNED_BYTE, @Pixels
38.   '
39.  return 0
40.   '
41.  

Texture binding as before

Code: OxygenBasic

1.  
2.   glbegin GL_QUADS
3.   '
4.  glTexCoord2f 0,0 : glvertex3f -sx, -sy,  sZ 'BOTTOM LEFT
5.  glTexCoord2f 0,1 : glvertex3f -sx,  sy,  sZ 'TOP LEFT
6.  glTexCoord2f 1,1 : glvertex3f  sx,  sy,  sZ 'TOP RIGHT
7.  glTexCoord2f 1,0 : glvertex3f  sx, -sy,  sZ 'BOTTOM RIGHT
8.  '
9.  glend
10.  

Charles

[Charles Pegge]

Do any of the other Opengl examples crash your PC Peter? This one is based on the examples/OpenglWin series. The only significant difference is the pixels texture making routine.

Charles