OpenGL fixed coordinate transformations -

was trying rendering opengl , happened think that: how run transformations in fixed coordinate system. in other words, if rotate object around 1 axis see others going rotate too? therefore, following rotations done on newly construct axis.

i read on documentation (see part 9.070 ) https://www.opengl.org/archives/resources/faq/technical/transformations.htm, have no idea: 1. if works 2. how implement cause don't understand supposed do.

i think won't 1 want , it's guess interesting question.

edit: here implementation doesn't work , fix

evoid display() { glclear(gl_color_buffer_bit | gl_depth_buffer_bit); // clear color , depth buffers glmatrixmode(gl_modelview);     // operate on model-view matrix  // render color-cube consisting of 6 quads different colors glloadidentity();                 // reset model-view matrix  gltranslatef(1.5f, 0.0f, -7.0f);  // move right , screen //glrotatef(anglecube, 1.0f, 1.0f, 1.0f);  // rotate (1,1,1)-axis [new]   //matrix transformation matrix obtained translation, scale , rotation composition   // in other piece of code wanted try   // matrix float[16] , values correct , updated every , make cube rotate   glmultmatrixf(matrix); glbegin(gl_quads);                // begin drawing color cube 6 quads   // top face (y = 1.0f)   // define vertices in counter-clockwise (ccw) order normal pointing out   glcolor3f(0.0f, 1.0f, 0.0f);     // green   glvertex3f( 1.0f, 1.0f, -1.0f);   glvertex3f(-1.0f, 1.0f, -1.0f);   glvertex3f(-1.0f, 1.0f,  1.0f);   glvertex3f( 1.0f, 1.0f,  1.0f);    // bottom face (y = -1.0f)   glcolor3f(1.0f, 0.5f, 0.0f);     // orange   glvertex3f( 1.0f, -1.0f,  1.0f);   glvertex3f(-1.0f, -1.0f,  1.0f);   glvertex3f(-1.0f, -1.0f, -1.0f);   glvertex3f( 1.0f, -1.0f, -1.0f);    // front face  (z = 1.0f)   glcolor3f(1.0f, 0.0f, 0.0f);     // red   glvertex3f( 1.0f,  1.0f, 1.0f);   glvertex3f(-1.0f,  1.0f, 1.0f);   glvertex3f(-1.0f, -1.0f, 1.0f);   glvertex3f( 1.0f, -1.0f, 1.0f);    // face (z = -1.0f)   glcolor3f(1.0f, 1.0f, 0.0f);     // yellow   glvertex3f( 1.0f, -1.0f, -1.0f);   glvertex3f(-1.0f, -1.0f, -1.0f);   glvertex3f(-1.0f,  1.0f, -1.0f);   glvertex3f( 1.0f,  1.0f, -1.0f);    // left face (x = -1.0f)   glcolor3f(0.0f, 0.0f, 1.0f);     // blue   glvertex3f(-1.0f,  1.0f,  1.0f);   glvertex3f(-1.0f,  1.0f, -1.0f);   glvertex3f(-1.0f, -1.0f, -1.0f);   glvertex3f(-1.0f, -1.0f,  1.0f);    // right face (x = 1.0f)   glcolor3f(1.0f, 0.0f, 1.0f);     // magenta   glvertex3f(1.0f,  1.0f, -1.0f);   glvertex3f(1.0f,  1.0f,  1.0f);   glvertex3f(1.0f, -1.0f,  1.0f);   glvertex3f(1.0f, -1.0f, -1.0f); glend();  // end of drawing color-cube 

the opengl modelview matrix works stack. every transformation performed post-multiplying transformation current mvm matrix. in other words, looks this:

new_mvm = old_mvm * transformation 

this causes transformations occur in local coordinate system. article states, need transformation work in fixed-coordinates system ("global coordinates"), need pre-multiply this:

new_mvm = transformation * old_mvm 

note instead of retrieving mvm opengl article specifies, can store transformation matrix object data member. each time want transform object, pre-multiply new transformation old one.

once have computed final transformation matrix object pre-multiplying, can pass opengl calling glmultmatrix.

---

edit: since need calculate matrix yourself, you're going want math library. if you're using glm, can like:

when rotating object:

glm::vec3 axis(x, y, z); glm::mat4 rotation = glm::rotate(glm::mat4(1.0f), angle_in_degrees, axis); totaltransform = rotation * totaltransform; 

then in 'display' method:

float *matptr = glm::value_ptr(totaltransform); glmultmatrixf(matptr); 

disclaimer: code untested.