CODEWITHSUNDEEP
c++opengl
user3231178
user3231178

Reputation: 11

glRotatef moves the axes

I'm trying OpenGL for the first time, so I want to code a simple program that displays a box and lets me move the camera.

As there is no such thing as a camera in OpenGL, I just simulate every "camera movement" I want by making the whole world move in the exact opposite way. It goes well until I get to rotations.

What happens is that whenever I rotate the world (glRotatef(10, 0, 1, 0);) the axes get rotated as well, so when I try to apply other transformations, such as (glTranslatef(0, 0, -10);) that would before move the world closer to the camera, it now moves in a totally different direction.

How should I proceed to solve that?

Upvotes: 1

Views: 333

Answers (1)

Pedro Boechat
Pedro Boechat

Reputation: 2576

First, you could use matrices to accumulate the transforms of your camera, just like OpenGL does.

But instead of using glRotate or glTransform, you could use a vector math library (i.e.: GLM) and apply analog operations (i.e.: glm::rotate, glm::translate) on a matrix variable (i.e: glm::mat4) you would call the 'local transforms' of your camera object.

Whenever you want to apply transforms on a different space (i.e.: (1,0,0)(0,1,0)(0,0,-1)) you just use a plain new matrix (just like glPopMatrix would do), something you would call 'world transform'.

At the end of each frame you would multiply both matrices (local * world) and use this result to feed OpenGL with a view matrix (i.e.: glMatrixMode(GL_MODELVIEW); glLoadMatrix(&(local * world)[0]);)

Oh, and don't forget to reset your 'world transform' matrix at the end of your frame.

Upvotes: 1

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