OpenGL: scale then translate? and how?

by

In OpenGL, matrices you specify are multiplied to the right of the existing matrix, and the vertex is on the far right of the expression.

Thus, the last operation you specify are in the coordinate system of the geometry itself.
(The first is usually the view transform, i.e. inverse of your camera’s to-world transform.)

Bahbar makes a good point that you need to consider the center point for scaling. (or the pivot point for rotations.) Usually you translate there, rotate/scale, then translate back. (or in general, apply basis transform, the operation, then the inverse). This is called Change of Basis, which you might want to read up on.

Anyway, to get some intuition about how it works, try with some simple values (zero, etc) then alter them slightly (perhaps an animation) and see what happens with the output. Then it’s much easier to see what your transforms are actually doing to your geometry.

Update

That the order is “reversed” w.r.t. intuition is rather common among beginner OpenGL-coders. I’ve been tutoring a computer graphics course and many react in a similar manner. It becomes easier to think about how OpenGL does it if you consider the use of pushmatrix/popmatrix while rendering a tree (scene-graph) of transforms and geometries. Then the current order-of-things becomes rather natural, and the opposite would make it rather difficult to get anything useful done.

More Related Contents:

  1. how should i handle (morphing) 4D objects in opengl? [closed]
  2. How to use GLUT/OpenGL to render to a file?
  3. How to implement 2D raycasting light effect in GLSL
  4. Getting the true z value from the depth buffer
  5. How exactly does OpenGL do perspectively correct linear interpolation?
  6. Why does OpenGL not support multiple index buffering?
  7. What does glLoadIdentity() do in OpenGL?
  8. Convert Quaternion rotation to rotation matrix?
  9. how openGL handles data service like socket service or http service? [closed]
  10. How to render depth linearly in modern OpenGL with gl_FragCoord.z in fragment shader?
  11. How does OpenGL work at the lowest level? [closed]
  12. What does “immediate mode” mean in OpenGL?
  13. What is the proper way to modify OpenGL vertex buffer?
  14. Is OpenGL coordinate system left-handed or right-handed?
  15. Passing a list of values to fragment shader
  16. In a fragment shader, why can’t I use a flat input integer to index a uniform array of sampler2D?
  17. Render OpenGL scene to texture using FBO in fixed function pipeline drawing
  18. How to draw text using only OpenGL methods?
  19. How to debug a GLSL shader?
  20. Why does GL divide `gl_Position` by W for you rather than letting you do it yourself?
  21. How to use Pivot Point in Transformations
  22. OpenGL translation before and after a rotation
  23. What exactly are eye space coordinates?
  24. OpenGL 2 Texture Internal Formats GL_RGB8I, GL_RGB32UI, etc
  25. How do you install GLUT and OpenGL in Visual Studio 2012?
  26. GLUT exit redefinition error
  27. What are Vertex Array Objects?
  28. From RGB to HSV in OpenGL GLSL
  29. Current state and solutions for OpenGL over Windows Remote [closed]
  30. GLSL – Using custom output attribute instead of gl_Position

Leave a Comment