opengl - Unexpected projection -


it should rect, takes whole width of window. expecting this, because frustum width -5 5 , rect size 10x10 , rect on same z-axis position near plnane of frustum. result small , doesn't rect, don't know why?

void glwidget::initializegl() {      glclearcolor(1.0f, 1.0f, 1.0f, 0.0f); }  void glwidget::resizegl(int w, int h) {      glviewport(0,0, w, h);     glmatrixmode(gl_projection);     double ratio = (double)w/(double)h;     double size = ((10.0/ratio)/2.0);     glfrustum(-5.0, 5.0, -size, size, 10.0, 50.0);  }  void glwidget::paintgl() {      glclear(gl_color_buffer_bit | gl_depth_buffer_bit);      glmatrixmode(gl_modelview);     glloadidentity();     gltranslatef(0.0f, 0.0f, -10.0f);      glcolor3f(0.0f, 0.0f, 0.0f);     glbegin(gl_quads);     glvertex3f(5.0f, -5.0f, 0.0f);     glvertex3f(5.0f, 5.0f, 0.0f);     glvertex3f(-5.0f, 5.0f, 0.0f);     glvertex3f(-5.0f, -5.0f, 0.0f);     glend();      glflush();   }

it should rect, takes whole width of window.

well, switch projection better suited, ortho projection, task when drawing rect. must reset projection matrix identity before applying frustum or ortho.

hint: code in resizegl should go paintgl method. see you're using qt, can widget's width , height conveniently using width , height getter functions. glclearcolor goes paingl well:

void glwidget::initializegl() { }  void glwidget::resizegl(int w, int h) {   }  void glwidget::paintgl() {     double const ratio = (double)width()/(double)height();     double const size = ((10.0/ratio)/2.0);      glclearcolor(1.0f, 1.0f, 1.0f, 0.0f);     glclear(gl_color_buffer_bit | gl_depth_buffer_bit);      glviewport(0,0, width(), height());     glmatrixmode(gl_projection);     glloadidentity();     glfrustum(-5.0, 5.0, -size, size, 10.0, 50.0);      glmatrixmode(gl_modelview);     glloadidentity();     gltranslatef(0.0f, 0.0f, -10.0f);      draw_perspective_stuff();      glviewport(0,0, width(), height());     glmatrixmode(gl_projection);     glloadidentity();      glmatrixmode(gl_modelview);     glloadidentity();      // using identity projection, fills viewport     glcolor3f(0.0f, 0.0f, 0.0f);     glbegin(gl_quads);     glvertex3f(-1.f, -1.f, 0.0f);     glvertex3f( 1.f, -1.f, 0.0f);     glvertex3f( 1.f,  1.f, 0.0f);     glvertex3f(-1.f,  1.f, 0.0f);     glend();      glflush(); }

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